diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index df1d5518b7..fb9c6a68e3 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -66,3 +66,10 @@ repos:
   hooks:
     - id: check-github-workflows
       args: ["--verbose"]
+
+- repo: https://github.com/pre-commit/mirrors-mypy
+  rev: v1.6.1
+  hooks:
+    - id: mypy
+      additional_dependencies:
+        - numpy>=1.24
diff --git a/pyproject.toml b/pyproject.toml
index bab2387515..c9081e4472 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -220,40 +220,21 @@ disable = [
 
 [tool.mypy]
 files = ["src/awkward/**/*.py"]
-exclude = ["^src/awkward/[^/]+\\.py$"]
 plugins = [
     "numpy.typing.mypy_plugin"
 ]
 python_version = "3.11"
+ignore_errors = true
+ignore_missing_imports = true
 
 [[tool.mypy.overrides]]
 module = [
-    'awkward.__init__',
-    'awkward._connect.*',
-    'awkward._cpu_kernels',
-    'awkward._errors',
-    'awkward._kernel_signatures',
-    'awkward._libawkward',
-    'awkward._util',
-    'awkward.forms',
-    'awkward.forth',
-    'awkward.highlevel',
-    'awkward.nplike',
-    'awkward.numba',
-    'awkward.types',
-    'awkward.types._awkward_datashape_parser',
-    'numba.*',
-    'llvmlite.*',
-    'ROOT.*',
-    'cppyy.*',
-    'jax.*',
-    'pandas.*',
-    'cupy.*',
-    'pyarrow.*',
-    'fsspec.*',
-    'numexpr.*',
+    'awkward._nplikes.*',
+    'awkward._behavior.*',
+    'awkward._backends.*',
+    'awkward.forms.*',
 ]
-ignore_errors = true
+ignore_errors = false
 ignore_missing_imports = true
 
 [tool.ruff]
@@ -306,6 +287,7 @@ mccabe.max-complexity = 100
 [tool.ruff.lint.per-file-ignores]
 "dev/*" = ["T20", "TID251"]
 "src/awkward/numba/*" = ["TID251"]
+"src/awkward/_typing.py" = ["TID251"]
 "src/awkward/_errors.py" = ["TID251"]
 "src/awkward/errors.py" = ["TID251"]
 "src/awkward/_connect/*" = ["TID251"]
diff --git a/src/awkward/_backends/backend.py b/src/awkward/_backends/backend.py
index f7a927c4ce..e815c8be2e 100644
--- a/src/awkward/_backends/backend.py
+++ b/src/awkward/_backends/backend.py
@@ -2,20 +2,21 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
+from typing import Any
 
 import awkward as ak
 from awkward._kernels import KernelError
 from awkward._nplikes.numpy import Numpy
 from awkward._nplikes.numpylike import NumpyLike, NumpyMetadata
 from awkward._singleton import PublicSingleton
-from awkward._typing import Callable, Tuple, TypeAlias, TypeVar, Unpack
+from awkward._typing import Callable, Tuple, TypeAlias, TypeVar
 
 np = NumpyMetadata.instance()
 numpy = Numpy.instance()
 
 
 T_co = TypeVar("T_co", covariant=True)
-KernelKeyType: TypeAlias = Tuple[str, Unpack[Tuple[np.dtype, ...]]]
+KernelKeyType: TypeAlias = Tuple[Any, ...]
 KernelType: TypeAlias = "Callable[..., KernelError | None]"
 
 
@@ -49,6 +50,7 @@ def format_kernel_error(
                 errors="surrogateescape"
             ).lstrip("\n").lstrip("(")
 
+        assert error.str is not None
         message = error.str.decode(errors="surrogateescape")
 
         if error.attempt != ak._util.kSliceNone:
diff --git a/src/awkward/_backends/cupy.py b/src/awkward/_backends/cupy.py
index 2bce1cb764..ce5ff53bc2 100644
--- a/src/awkward/_backends/cupy.py
+++ b/src/awkward/_backends/cupy.py
@@ -13,7 +13,7 @@
 numpy = Numpy.instance()
 
 
-@register_backend(Cupy)
+@register_backend(Cupy)  # type: ignore[type-abstract]
 class CupyBackend(Backend):
     name: Final[str] = "cuda"
 
diff --git a/src/awkward/_backends/dispatch.py b/src/awkward/_backends/dispatch.py
index 4150364244..16fe82b9dd 100644
--- a/src/awkward/_backends/dispatch.py
+++ b/src/awkward/_backends/dispatch.py
@@ -6,8 +6,8 @@
 from awkward._backends.backend import Backend
 from awkward._nplikes.numpy import Numpy
 from awkward._nplikes.numpylike import NumpyLike, NumpyMetadata
-from awkward._typing import Callable, TypeAlias, TypeVar
-from awkward._util import UNSET
+from awkward._typing import Callable, TypeAlias, TypeVar, cast
+from awkward._util import UNSET, Sentinel
 
 np = NumpyMetadata.instance()
 numpy = Numpy.instance()
@@ -19,7 +19,7 @@
 BackendLookupFactory: TypeAlias = "Callable[[type[T]], BackendLookup[T]]"
 
 
-_type_to_backend_lookup: dict[type[T], BackendLookup] = {}
+_type_to_backend_lookup: dict[type, BackendLookup] = {}
 _backend_lookup_factories: list[BackendLookupFactory] = []
 _name_to_backend_cls: dict[str, type[Backend]] = {}
 
@@ -68,7 +68,7 @@ def common_backend(backends: Collection[Backend]) -> Backend:
             )
 
 
-def backend_of_obj(obj, default: D = UNSET) -> Backend | D:
+def backend_of_obj(obj, default: D | Sentinel = UNSET) -> Backend | D:
     cls = type(obj)
     try:
         lookup = _type_to_backend_lookup[cls]
@@ -82,13 +82,13 @@ def backend_of_obj(obj, default: D = UNSET) -> Backend | D:
             if default is UNSET:
                 raise TypeError(f"cannot find backend for {cls.__name__}")
             else:
-                return default
+                return cast(D, default)
         _type_to_backend_lookup[cls] = maybe_lookup
         return maybe_lookup(obj)
 
 
 def backend_of(
-    *objects, default: D = UNSET, coerce_to_common: bool = False
+    *objects, default: D | Sentinel = UNSET, coerce_to_common: bool = False
 ) -> Backend | D:
     """
     Args:
@@ -108,7 +108,7 @@ def backend_of(
         if default is UNSET:
             raise ValueError("could not find backend for", objects)
         else:
-            return default
+            return cast(D, default)
     elif len(unique_backends) == 1:
         return next(iter(unique_backends))
     elif coerce_to_common:
diff --git a/src/awkward/_backends/jax.py b/src/awkward/_backends/jax.py
index ef63dca017..4f53837698 100644
--- a/src/awkward/_backends/jax.py
+++ b/src/awkward/_backends/jax.py
@@ -16,7 +16,7 @@
 numpy = Numpy.instance()
 
 
-@register_backend(Jax)
+@register_backend(Jax)  # type: ignore[type-abstract]
 class JaxBackend(Backend):
     name: Final[str] = "jax"
 
diff --git a/src/awkward/_backends/numpy.py b/src/awkward/_backends/numpy.py
index b40817b729..e8ea90f2d0 100644
--- a/src/awkward/_backends/numpy.py
+++ b/src/awkward/_backends/numpy.py
@@ -14,7 +14,7 @@
 numpy = Numpy.instance()
 
 
-@register_backend(Numpy)
+@register_backend(Numpy)  # type: ignore[type-abstract]
 class NumpyBackend(Backend):
     name: Final[str] = "cpu"
 
diff --git a/src/awkward/_backends/typetracer.py b/src/awkward/_backends/typetracer.py
index cef237ed21..d9ef2e5668 100644
--- a/src/awkward/_backends/typetracer.py
+++ b/src/awkward/_backends/typetracer.py
@@ -13,7 +13,7 @@
 numpy = Numpy.instance()
 
 
-@register_backend(TypeTracer)
+@register_backend(TypeTracer)  # type: ignore[type-abstract]
 class TypeTracerBackend(Backend):
     name: Final[str] = "typetracer"
 
diff --git a/src/awkward/_behavior.py b/src/awkward/_behavior.py
index 8433c3199a..4f4f6bea26 100644
--- a/src/awkward/_behavior.py
+++ b/src/awkward/_behavior.py
@@ -2,14 +2,22 @@
 from __future__ import annotations
 
 from collections import ChainMap
-from collections.abc import Mapping
+from collections.abc import Callable, Mapping
 
 import awkward as ak
 from awkward._nplikes import ufuncs
-from awkward._typing import Any
+from awkward._typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from awkward._nplikes.numpylike import UfuncLike
+    from awkward._reducers import Reducer
+    from awkward.contents.content import Content
+    from awkward.highlevel import Array
+    from awkward.highlevel import Record as HighLevelRecord
+    from awkward.record import Record
 
 
-def overlay_behavior(behavior: dict | None) -> Mapping:
+def overlay_behavior(behavior: Mapping | None) -> Mapping:
     """
     Args:
         behavior: behavior dictionary, or None
@@ -19,10 +27,11 @@ def overlay_behavior(behavior: dict | None) -> Mapping:
     """
     if behavior is None:
         return ak.behavior
-    return ChainMap(behavior, ak.behavior)
+    else:
+        return ChainMap(behavior, ak.behavior)  # type: ignore[arg-type]
 
 
-def get_array_class(layout, behavior):
+def get_array_class(layout: Content, behavior: Mapping | None) -> type[Array]:
     from awkward.highlevel import Array
 
     behavior = overlay_behavior(behavior)
@@ -39,7 +48,7 @@ def get_array_class(layout, behavior):
     return Array
 
 
-def get_record_class(layout, behavior):
+def get_record_class(layout: Record, behavior: Mapping | None) -> type[HighLevelRecord]:
     from awkward.highlevel import Record
 
     behavior = overlay_behavior(behavior)
@@ -51,14 +60,20 @@ def get_record_class(layout, behavior):
     return Record
 
 
-def find_record_reducer(reducer, layout, behavior):
+def find_record_reducer(
+    reducer: Reducer, layout: Record, behavior: Mapping | None
+) -> Callable[[Array, bool], Any] | None:
     behavior = overlay_behavior(behavior)
     rec = layout.parameter("__record__")
     if isinstance(rec, str):
         return behavior.get((reducer.highlevel_function(), rec))
+    else:
+        return None
 
 
-def find_custom_cast(obj, behavior):
+def find_custom_cast(
+    obj: Any, behavior: Mapping | None
+) -> Callable[[Any], Content | Record] | None:
     behavior = overlay_behavior(behavior)
     for cls in type(obj).__mro__:
         fcn = behavior.get(("__cast__", cls))
@@ -67,7 +82,9 @@ def find_custom_cast(obj, behavior):
     return None
 
 
-def find_ufunc_generic(ufunc, layout, behavior):
+def find_ufunc_generic(
+    ufunc: UfuncLike, layout: Content, behavior: Mapping | None
+) -> Callable[[UfuncLike, str, list, dict], Any] | None:
     behavior = overlay_behavior(behavior)
     custom = layout.parameter("__list__")
     if custom is None:
@@ -81,8 +98,8 @@ def find_ufunc_generic(ufunc, layout, behavior):
         return None
 
 
-def find_ufunc(behavior, signature: tuple):
-    if not any(s is None for s in signature):
+def find_ufunc(behavior: Mapping | None, signature: tuple) -> UfuncLike | None:
+    if all(s is not None for s in signature):
         behavior = overlay_behavior(behavior)
 
         # Special case all strings or hashable types.
@@ -105,13 +122,14 @@ def find_ufunc(behavior, signature: tuple):
                     )
                 ):
                     return custom
+    return None
 
 
 def find_record_typestr(
     behavior: None | Mapping,
     parameters: None | Mapping[str, Any],
     default: str | None = None,
-):
+) -> str | None:
     if parameters is None:
         return default
     behavior = overlay_behavior(behavior)
@@ -122,14 +140,14 @@ def find_array_typestr(
     behavior: None | Mapping,
     parameters: None | Mapping[str, Any],
     default: str | None = None,
-):
+) -> str | None:
     if parameters is None:
         return default
     behavior = overlay_behavior(behavior)
     return behavior.get(("__typestr__", parameters.get("__list__")), default)
 
 
-def behavior_of_obj(obj, behavior: Mapping | None = None) -> Mapping | None:
+def behavior_of_obj(obj: Any, behavior: Mapping | None = None) -> Mapping | None:
     from awkward.highlevel import Array, ArrayBuilder, Record
 
     if behavior is not None:
@@ -140,7 +158,7 @@ def behavior_of_obj(obj, behavior: Mapping | None = None) -> Mapping | None:
         return None
 
 
-def behavior_of(*arrays, behavior: Mapping | None = None) -> Mapping | None:
+def behavior_of(*arrays: Any, behavior: Mapping | None = None) -> Mapping | None:
     if behavior is not None:
         # An explicit 'behavior' always wins.
         return behavior
@@ -158,5 +176,6 @@ def behavior_of(*arrays, behavior: Mapping | None = None) -> Mapping | None:
             behavior.update(x_behavior)
             copied = True
         else:
+            assert isinstance(behavior, dict)
             behavior.update(x_behavior)
     return behavior
diff --git a/src/awkward/_kernels.py b/src/awkward/_kernels.py
index b0f418a052..e5b3b979f3 100644
--- a/src/awkward/_kernels.py
+++ b/src/awkward/_kernels.py
@@ -21,8 +21,8 @@
 
 
 class KernelError(Protocol):
-    filename: str | None  # pylint: disable=E0602
-    str: str | None
+    filename: bytes | None  # pylint: disable=E0602
+    str: bytes | None
     attempt: int
     id: int
 
diff --git a/src/awkward/_nplikes/__init__.py b/src/awkward/_nplikes/__init__.py
index 83cada5622..eddedce0c6 100644
--- a/src/awkward/_nplikes/__init__.py
+++ b/src/awkward/_nplikes/__init__.py
@@ -33,6 +33,6 @@ def to_nplike(
     if isinstance(from_nplike, awkward._nplikes.cupy.Cupy) and not isinstance(
         nplike, awkward._nplikes.cupy.Cupy
     ):
-        array = array.get()
+        array = array.get()  # type: ignore[attr-defined]
 
     return nplike.asarray(array)
diff --git a/src/awkward/_nplikes/array_module.py b/src/awkward/_nplikes/array_module.py
index 88d5d93de7..25c3df20b8 100644
--- a/src/awkward/_nplikes/array_module.py
+++ b/src/awkward/_nplikes/array_module.py
@@ -17,7 +17,10 @@
 )
 from awkward._nplikes.placeholder import PlaceholderArray
 from awkward._nplikes.shape import ShapeItem, unknown_length
-from awkward._typing import Any, cast, Final, Literal, DType
+from awkward._typing import TYPE_CHECKING, Any, Final, Literal, cast
+
+if TYPE_CHECKING:
+    from numpy.typing import DTypeLike
 
 np = NumpyMetadata.instance()
 NUMPY_HAS_NEP_50 = packaging.version.Version(
@@ -49,7 +52,7 @@ def asarray(
         self,
         obj,
         *,
-        dtype: DType | None = None,
+        dtype: DTypeLike | None = None,
         copy: bool | None = None,
     ) -> ArrayLike:
         if isinstance(obj, PlaceholderArray):
@@ -74,7 +77,7 @@ def ascontiguousarray(self, x: ArrayLike) -> ArrayLike:
             return self._module.ascontiguousarray(x)
 
     def frombuffer(
-        self, buffer, *, dtype: DType | None = None, count: ShapeItem = -1
+        self, buffer, *, dtype: DTypeLike | None = None, count: ShapeItem = -1
     ) -> ArrayLike:
         if isinstance(buffer, PlaceholderArray):
             raise TypeError("placeholder arrays are not supported in `frombuffer`")
@@ -84,17 +87,26 @@ def from_dlpack(self, x: Any) -> ArrayLike:
         return self._module.from_dlpack(x)
 
     def zeros(
-        self, shape: ShapeItem | tuple[ShapeItem, ...], *, dtype: DType | None = None
+        self,
+        shape: ShapeItem | tuple[ShapeItem, ...],
+        *,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         return self._module.zeros(shape, dtype=dtype)
 
     def ones(
-        self, shape: ShapeItem | tuple[ShapeItem, ...], *, dtype: DType | None = None
+        self,
+        shape: ShapeItem | tuple[ShapeItem, ...],
+        *,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         return self._module.ones(shape, dtype=dtype)
 
     def empty(
-        self, shape: ShapeItem | tuple[ShapeItem, ...], *, dtype: DType | None = None
+        self,
+        shape: ShapeItem | tuple[ShapeItem, ...],
+        *,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         return self._module.empty(shape, dtype=dtype)
 
@@ -103,24 +115,24 @@ def full(
         shape: ShapeItem | tuple[ShapeItem, ...],
         fill_value,
         *,
-        dtype: DType | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         return self._module.full(shape, fill_value, dtype=dtype)
 
-    def zeros_like(self, x: ArrayLike, *, dtype: DType | None = None) -> ArrayLike:
+    def zeros_like(self, x: ArrayLike, *, dtype: DTypeLike | None = None) -> ArrayLike:
         if isinstance(x, PlaceholderArray):
             return self.zeros(x.shape, dtype=dtype or x.dtype)
         else:
             return self._module.zeros_like(x, dtype=dtype)
 
-    def ones_like(self, x: ArrayLike, *, dtype: DType | None = None) -> ArrayLike:
+    def ones_like(self, x: ArrayLike, *, dtype: DTypeLike | None = None) -> ArrayLike:
         if isinstance(x, PlaceholderArray):
             return self.ones(x.shape, dtype=dtype or x.dtype)
         else:
             return self._module.ones_like(x, dtype=dtype)
 
     def full_like(
-        self, x: ArrayLike, fill_value, *, dtype: DType | None = None
+        self, x: ArrayLike, fill_value, *, dtype: DTypeLike | None = None
     ) -> ArrayLike:
         if isinstance(x, PlaceholderArray):
             return self.full(x.shape, fill_value, dtype=dtype or x.dtype)
@@ -133,7 +145,7 @@ def arange(
         stop: float | int | None = None,
         step: float | int = 1,
         *,
-        dtype: DType | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         assert not isinstance(start, PlaceholderArray)
         assert not isinstance(stop, PlaceholderArray)
@@ -212,14 +224,13 @@ def apply_ufunc(
         ) -> ArrayLike | tuple[ArrayLike]:
             # Convert np.generic to scalar arrays
             resolved_args = [
-                self.asarray(arg, dtype=arg.dtype) if hasattr(arg, "dtype") else arg
+                self.asarray(arg, dtype=arg.dtype if hasattr(arg, "dtype") else None)
                 for arg in args
             ]
             broadcasted_args = self.broadcast_arrays(*resolved_args)
             # Choose the broadcasted argument if it wasn't a Python scalar
             non_generic_value_promoted_args = [
-                y if hasattr(x, "ndim") else x
-                for x, y in zip(resolved_args, broadcasted_args)
+                y if hasattr(x, "ndim") else x for x, y in zip(args, broadcasted_args)
             ]
             # Allow other nplikes to replace implementation
             impl = self.prepare_ufunc(ufunc)
@@ -436,7 +447,7 @@ def broadcast_to(self, x: ArrayLike, shape: tuple[ShapeItem, ...]) -> ArrayLike:
     def strides(self, x: ArrayLike) -> tuple[ShapeItem, ...]:
         if isinstance(x, PlaceholderArray):
             # Assume contiguous
-            strides: tuple[int, ...] = (x.itemsize,)
+            strides: tuple[ShapeItem, ...] = (x.dtype.itemsize,)
             for item in x.shape[-1:0:-1]:
                 strides = (item * strides[0], *strides)
             return strides
@@ -598,12 +609,12 @@ def array_str(
         )
 
     def astype(
-        self, x: ArrayLike, dtype: numpy.dtype, *, copy: bool | None = True
+        self, x: ArrayLike, dtype: DTypeLike, *, copy: bool | None = True
     ) -> ArrayLike:
         assert not isinstance(x, PlaceholderArray)
-        return x.astype(dtype, copy=copy)  # type: ignore
+        return x.astype(dtype, copy=copy)  # type: ignore[attr-defined]
 
-    def can_cast(self, from_: DType | ArrayLike, to: DType | ArrayLike) -> bool:
+    def can_cast(self, from_: DTypeLike | ArrayLike, to: DTypeLike | ArrayLike) -> bool:
         return self._module.can_cast(from_, to, casting="same_kind")
 
     @classmethod
diff --git a/src/awkward/_nplikes/cupy.py b/src/awkward/_nplikes/cupy.py
index f242447407..d278945ec4 100644
--- a/src/awkward/_nplikes/cupy.py
+++ b/src/awkward/_nplikes/cupy.py
@@ -8,7 +8,11 @@
 from awkward._nplikes.dispatch import register_nplike
 from awkward._nplikes.numpylike import ArrayLike
 from awkward._nplikes.placeholder import PlaceholderArray
-from awkward._typing import Final
+from awkward._nplikes.shape import ShapeItem
+from awkward._typing import TYPE_CHECKING, Final
+
+if TYPE_CHECKING:
+    from numpy.typing import DTypeLike
 
 
 @register_nplike
@@ -40,7 +44,7 @@ def ndarray(self):
         return self._module.ndarray
 
     def frombuffer(
-        self, buffer, *, dtype: numpy.dtype | None = None, count: int = -1
+        self, buffer, *, dtype: DTypeLike | None = None, count: ShapeItem = -1
     ) -> ArrayLike:
         assert not isinstance(buffer, PlaceholderArray)
         assert not isinstance(count, PlaceholderArray)
@@ -81,7 +85,7 @@ def all(
         self,
         x: ArrayLike,
         *,
-        axis: int | tuple[int, ...] | None = None,
+        axis: ShapeItem | tuple[ShapeItem, ...] | None = None,
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> ArrayLike:
@@ -96,7 +100,7 @@ def any(
         self,
         x: ArrayLike,
         *,
-        axis: int | tuple[int, ...] | None = None,
+        axis: ShapeItem | tuple[ShapeItem, ...] | None = None,
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> ArrayLike:
@@ -108,7 +112,7 @@ def any(
             return out
 
     def count_nonzero(
-        self, x: ArrayLike, *, axis: int | tuple[int, ...] | None = None
+        self, x: ArrayLike, *, axis: ShapeItem | tuple[ShapeItem, ...] | None = None
     ) -> ArrayLike:
         assert not isinstance(x, PlaceholderArray)
         assert isinstance(axis, int) or axis is None
@@ -122,7 +126,7 @@ def min(
         self,
         x: ArrayLike,
         *,
-        axis: int | tuple[int, ...] | None = None,
+        axis: ShapeItem | tuple[ShapeItem, ...] | None = None,
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> ArrayLike:
@@ -137,7 +141,7 @@ def max(
         self,
         x: ArrayLike,
         *,
-        axis: int | tuple[int, ...] | None = None,
+        axis: ShapeItem | tuple[ShapeItem, ...] | None = None,
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> ArrayLike:
@@ -164,4 +168,4 @@ def is_c_contiguous(self, x: ArrayLike) -> bool:
         if isinstance(x, PlaceholderArray):
             return True
         else:
-            return x.flags["C_CONTIGUOUS"]
+            return x.flags["C_CONTIGUOUS"]  # type: ignore[attr-defined]
diff --git a/src/awkward/_nplikes/dispatch.py b/src/awkward/_nplikes/dispatch.py
index 3948dbf30b..6d6bd01c88 100644
--- a/src/awkward/_nplikes/dispatch.py
+++ b/src/awkward/_nplikes/dispatch.py
@@ -1,8 +1,8 @@
 from __future__ import annotations
 
 from awkward._nplikes.numpylike import NumpyLike
-from awkward._typing import TypeVar
-from awkward._util import UNSET
+from awkward._typing import Any, TypeVar, cast
+from awkward._util import UNSET, Sentinel
 
 D = TypeVar("D")
 
@@ -19,7 +19,7 @@ def register_nplike(cls: N) -> N:
     return cls
 
 
-def nplike_of_obj(obj, *, default: D = UNSET) -> NumpyLike | D:
+def nplike_of_obj(obj: Any, *, default: D | Sentinel = UNSET) -> NumpyLike | D:
     """
     Args:
         *arrays: iterable of possible array objects
@@ -44,6 +44,6 @@ def nplike_of_obj(obj, *, default: D = UNSET) -> NumpyLike | D:
             if default is UNSET:
                 raise TypeError(f"cannot find nplike for {cls.__name__}")
             else:
-                return default
+                return cast(D, default)
         _type_to_nplike[cls] = nplike
         return nplike
diff --git a/src/awkward/_nplikes/jax.py b/src/awkward/_nplikes/jax.py
index d1aeeb9ced..03d1fa74bb 100644
--- a/src/awkward/_nplikes/jax.py
+++ b/src/awkward/_nplikes/jax.py
@@ -5,8 +5,7 @@
 from awkward._nplikes.array_module import ArrayModuleNumpyLike
 from awkward._nplikes.dispatch import register_nplike
 from awkward._nplikes.numpylike import ArrayLike, UfuncLike
-from awkward._nplikes.shape import ShapeItem
-from awkward._typing import Final
+from awkward._typing import Final, cast
 
 
 @register_nplike
@@ -82,9 +81,8 @@ def is_c_contiguous(self, x: ArrayLike) -> bool:
     def ascontiguousarray(self, x: ArrayLike) -> ArrayLike:
         return x
 
-    def strides(self, x: ArrayLike) -> tuple[ShapeItem, ...]:
-        x.touch_shape()
-        out = (x._dtype.itemsize,)
-        for item in x._shape[-1:0:-1]:
+    def strides(self, x: ArrayLike) -> tuple[int, ...]:
+        out: tuple[int, ...] = (x.dtype.itemsize,)
+        for item in cast(tuple[int, ...], x.shape[-1:0:-1]):
             out = (item * out[0], *out)
         return out
diff --git a/src/awkward/_nplikes/numpy.py b/src/awkward/_nplikes/numpy.py
index 43497ab24d..e7ee6513b1 100644
--- a/src/awkward/_nplikes/numpy.py
+++ b/src/awkward/_nplikes/numpy.py
@@ -47,7 +47,7 @@ def is_c_contiguous(self, x: ArrayLike) -> bool:
         if isinstance(x, PlaceholderArray):
             return True
         else:
-            return x.flags["C_CONTIGUOUS"]
+            return x.flags["C_CONTIGUOUS"]  # type: ignore[attr-defined]
 
     def packbits(
         self,
@@ -57,7 +57,7 @@ def packbits(
         bitorder: Literal["big", "little"] = "big",
     ):
         assert not isinstance(x, PlaceholderArray)
-        return numpy.packbits(x, axis=axis, bitorder=bitorder)
+        return numpy.packbits(x, axis=axis, bitorder=bitorder)  # type: ignore[arg-type]
 
     def unpackbits(
         self,
@@ -68,4 +68,4 @@ def unpackbits(
         bitorder: Literal["big", "little"] = "big",
     ):
         assert not isinstance(x, PlaceholderArray)
-        return numpy.unpackbits(x, axis=axis, count=count, bitorder=bitorder)
+        return numpy.unpackbits(x, axis=axis, count=count, bitorder=bitorder)  # type: ignore[arg-type]
diff --git a/src/awkward/_nplikes/numpylike.py b/src/awkward/_nplikes/numpylike.py
index 26ac7c63a7..6e95402829 100644
--- a/src/awkward/_nplikes/numpylike.py
+++ b/src/awkward/_nplikes/numpylike.py
@@ -5,10 +5,12 @@
 
 import numpy
 
-from awkward._nplikes.shape import ShapeItem, unknown_length
+from awkward._nplikes.shape import ShapeItem
 from awkward._singleton import PublicSingleton
 from awkward._typing import (
+    TYPE_CHECKING,
     Any,
+    DType,
     Literal,
     NamedTuple,
     Protocol,
@@ -18,6 +20,12 @@
     overload,
 )
 
+if TYPE_CHECKING:
+    from types import EllipsisType
+
+    from numpy.typing import DTypeLike
+
+
 IndexType: TypeAlias = "int | ArrayLike"
 
 
@@ -31,7 +39,7 @@ class UniqueAllResult(NamedTuple):
 class ArrayLike(Protocol):
     @property
     @abstractmethod
-    def dtype(self) -> dtype:
+    def dtype(self) -> DType:
         ...
 
     @property
@@ -64,8 +72,8 @@ def __getitem__(
         self,
         key: SupportsIndex
         | slice
-        | Ellipsis
-        | tuple[SupportsIndex | slice | Ellipsis | ArrayLike, ...]
+        | EllipsisType
+        | tuple[SupportsIndex | slice | EllipsisType | ArrayLike, ...]
         | ArrayLike,
     ) -> Self:
         ...
@@ -73,23 +81,23 @@ def __getitem__(
     @overload
     def __setitem__(
         self,
-        key: SupportsIndex
-        | slice
-        | Ellipsis
-        | tuple[SupportsIndex | slice | Ellipsis | ArrayLike, ...]
+        key: slice
+        | EllipsisType
+        | tuple[SupportsIndex | slice | EllipsisType, ...]
         | ArrayLike,
-        value: int | float | bool | complex | ArrayLike,
+        value: int | float | bool | complex,
     ):
         ...
 
     @overload
     def __setitem__(
         self,
-        key: slice
-        | Ellipsis
-        | tuple[SupportsIndex | slice | Ellipsis, ...]
+        key: SupportsIndex
+        | slice
+        | EllipsisType
+        | tuple[SupportsIndex | slice | EllipsisType | ArrayLike, ...]
         | ArrayLike,
-        value: int | float | bool | complex,
+        value: int | float | bool | complex | ArrayLike,
     ):
         ...
 
@@ -114,7 +122,7 @@ def __len__(self) -> int:
         ...
 
     @abstractmethod
-    def view(self, dtype: dtype) -> Self:
+    def view(self, dtype: DType) -> Self:
         ...
 
     # Scalar UFUNCS
@@ -155,7 +163,7 @@ def __le__(self, other: int | complex | float | Self) -> Self:
         ...
 
     @abstractmethod
-    def __eq__(self, other: int | complex | float | bool | Self) -> Self:
+    def __eq__(self, other: int | complex | float | bool | Self) -> Self:  # type: ignore[override]
         ...
 
     @abstractmethod
@@ -170,9 +178,11 @@ def __or__(self, other: int | bool | Self) -> Self:
     def __invert__(self) -> Self:
         ...
 
+    @abstractmethod
     def __dlpack_device__(self) -> tuple[int, int]:
         ...
 
+    @abstractmethod
     def __dlpack__(self, stream: Any = None) -> Any:
         ...
 
@@ -195,6 +205,9 @@ class NumpyMetadata(PublicSingleton):
     str_ = numpy.str_
     bytes_ = numpy.bytes_
 
+    datetime64 = numpy.datetime64
+    timedelta64 = numpy.timedelta64
+
     intp = numpy.intp
     integer = numpy.integer
     signedinteger = numpy.signedinteger
@@ -208,8 +221,9 @@ class NumpyMetadata(PublicSingleton):
     dtype = numpy.dtype
     ufunc = numpy.ufunc
     iinfo = numpy.iinfo
+    finfo = numpy.finfo
     errstate = numpy.errstate
-    newaxis = numpy.newaxis
+    newaxis: None = numpy.newaxis
 
     ndarray = numpy.ndarray
 
@@ -217,29 +231,20 @@ class NumpyMetadata(PublicSingleton):
     inf = numpy.inf
 
     nat = numpy.datetime64("NaT")
-    datetime_data = numpy.datetime_data
-
-    @property
-    def issubdtype(self):
-        return numpy.issubdtype
+    datetime_data = staticmethod(numpy.datetime_data)
+    issubdtype = staticmethod(numpy.issubdtype)
 
     AxisError = numpy.AxisError
 
 
 if hasattr(numpy, "float16"):
-    NumpyMetadata.float16 = numpy.float16
+    NumpyMetadata.float16 = numpy.float16  # type: ignore[attr-defined]
 
 if hasattr(numpy, "float128"):
-    NumpyMetadata.float128 = numpy.float128
+    NumpyMetadata.float128 = numpy.float128  # type: ignore[attr-defined]
 
 if hasattr(numpy, "complex256"):
-    NumpyMetadata.complex256 = numpy.complex256
-
-if hasattr(numpy, "datetime64"):
-    NumpyMetadata.datetime64 = numpy.datetime64
-
-if hasattr(numpy, "timedelta64"):
-    NumpyMetadata.timedelta64 = numpy.timedelta64
+    NumpyMetadata.complex256 = numpy.complex256  # type: ignore[attr-defined]
 
 
 class UfuncLike(Protocol):
@@ -266,7 +271,7 @@ def apply_ufunc(
         method: str,
         args: list[Any],
         kwargs: dict[str, Any] | None = None,
-    ) -> ArrayLike | tuple[ArrayLike]:
+    ) -> ArrayLike | tuple[ArrayLike, ...]:
         ...
 
     @property
@@ -291,7 +296,7 @@ def asarray(
         self,
         obj,
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
         copy: bool | None = None,
     ) -> ArrayLike:
         ...
@@ -302,7 +307,7 @@ def ascontiguousarray(self, x: ArrayLike) -> ArrayLike:
 
     @abstractmethod
     def frombuffer(
-        self, buffer, *, dtype: numpy.dtype | None = None, count: int = -1
+        self, buffer, *, dtype: DTypeLike | None = None, count: ShapeItem = -1
     ) -> ArrayLike:
         ...
 
@@ -315,7 +320,7 @@ def zeros(
         self,
         shape: ShapeItem | tuple[ShapeItem, ...],
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         ...
 
@@ -324,7 +329,7 @@ def ones(
         self,
         shape: ShapeItem | tuple[ShapeItem, ...],
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         ...
 
@@ -333,7 +338,7 @@ def empty(
         self,
         shape: ShapeItem | tuple[ShapeItem, ...],
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         ...
 
@@ -343,23 +348,21 @@ def full(
         shape: ShapeItem | tuple[ShapeItem, ...],
         fill_value,
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         ...
 
     @abstractmethod
-    def zeros_like(
-        self, x: ArrayLike, *, dtype: numpy.dtype | None = None
-    ) -> ArrayLike:
+    def zeros_like(self, x: ArrayLike, *, dtype: DTypeLike | None = None) -> ArrayLike:
         ...
 
     @abstractmethod
-    def ones_like(self, x: ArrayLike, *, dtype: numpy.dtype | None = None) -> ArrayLike:
+    def ones_like(self, x: ArrayLike, *, dtype: DTypeLike | None = None) -> ArrayLike:
         ...
 
     @abstractmethod
     def full_like(
-        self, x: ArrayLike, fill_value, *, dtype: numpy.dtype | None = None
+        self, x: ArrayLike, fill_value, *, dtype: DTypeLike | None = None
     ) -> ArrayLike:
         ...
 
@@ -370,7 +373,7 @@ def arange(
         stop: float | int | None = None,
         step: float | int = 1,
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> ArrayLike:
         ...
 
@@ -385,7 +388,7 @@ def meshgrid(
     @abstractmethod
     def array_equal(
         self, x1: ArrayLike, x2: ArrayLike, *, equal_nan: bool = False
-    ) -> ArrayLike:
+    ) -> bool:
         ...
 
     @abstractmethod
@@ -409,16 +412,8 @@ def broadcast_arrays(self, *arrays: ArrayLike) -> list[ArrayLike]:
     def broadcast_to(self, x: ArrayLike, shape: tuple[ShapeItem, ...]) -> ArrayLike:
         ...
 
-    @overload
-    def shape_item_as_index(self, x1: int) -> int:
-        ...
-
-    @overload
-    def shape_item_as_index(self, x1: type[unknown_length]) -> ArrayLike:
-        ...
-
     @abstractmethod
-    def shape_item_as_index(self, x1):
+    def shape_item_as_index(self, x1: ShapeItem) -> int | ArrayLike:
         ...
 
     @abstractmethod
@@ -666,14 +661,12 @@ def array_str(
 
     @abstractmethod
     def astype(
-        self, x: ArrayLike, dtype: numpy.dtype, *, copy: bool | None = True
+        self, x: ArrayLike, dtype: DTypeLike, *, copy: bool | None = True
     ) -> ArrayLike:
         ...
 
     @abstractmethod
-    def can_cast(
-        self, from_: numpy.dtype | ArrayLike, to: numpy.dtype | ArrayLike
-    ) -> bool:
+    def can_cast(self, from_: DType | ArrayLike, to: DType | ArrayLike) -> bool:
         ...
 
     @abstractmethod
diff --git a/src/awkward/_nplikes/placeholder.py b/src/awkward/_nplikes/placeholder.py
index c401121d03..ea6ac07156 100644
--- a/src/awkward/_nplikes/placeholder.py
+++ b/src/awkward/_nplikes/placeholder.py
@@ -6,25 +6,23 @@
 
 from awkward._nplikes.numpylike import ArrayLike, NumpyLike, NumpyMetadata
 from awkward._nplikes.shape import ShapeItem, unknown_length
-from awkward._typing import Self
+from awkward._typing import Any, DType, Self
 
 np = NumpyMetadata.instance()
 
 
 class PlaceholderArray(ArrayLike):
-    def __init__(
-        self, nplike: NumpyLike, shape: tuple[ShapeItem, ...], dtype: np.dtype
-    ):
+    def __init__(self, nplike: NumpyLike, shape: tuple[ShapeItem, ...], dtype: DType):
         self._nplike = nplike
         self._shape = shape
         self._dtype = np.dtype(dtype)
 
     @property
-    def dtype(self) -> np.dtype:
+    def dtype(self) -> DType:
         return self._dtype
 
     @property
-    def shape(self) -> tuple[int, ...]:
+    def shape(self) -> tuple[ShapeItem, ...]:
         return self._shape
 
     @property
@@ -32,7 +30,7 @@ def ndim(self) -> int:
         return len(self._shape)
 
     @property
-    def size(self) -> int:
+    def size(self) -> ShapeItem:
         return reduce(mul, self._shape)
 
     @property
@@ -40,8 +38,8 @@ def nbytes(self) -> int:
         return 0
 
     @property
-    def strides(self) -> tuple[int, ...]:
-        out = (self._dtype.itemsize,)
+    def strides(self) -> tuple[ShapeItem, ...]:
+        out: tuple[ShapeItem, ...] = (self._dtype.itemsize,)
         for item in reversed(self._shape):
             out = (item * out[0], *out)
         return out
@@ -50,7 +48,7 @@ def strides(self) -> tuple[int, ...]:
     def T(self):
         return type(self)(self._nplike, self._shape[::-1], self._dtype)
 
-    def view(self, dtype: dtype) -> Self:
+    def view(self, dtype: DType) -> Self:
         dtype = np.dtype(dtype)
         if len(self._shape) >= 1:
             last, remainder = divmod(
@@ -108,7 +106,7 @@ def __index__(self) -> int:
         raise RuntimeError
 
     def __len__(self) -> int:
-        return self._shape[0]
+        return int(self._shape[0])
 
     def __add__(self, other):
         raise RuntimeError
@@ -149,4 +147,10 @@ def __sub__(self, other):
     def __truediv__(self, other):
         raise RuntimeError
 
-    __iter__ = None
+    __iter__: None = None
+
+    def __dlpack_device__(self) -> tuple[int, int]:
+        raise RuntimeError
+
+    def __dlpack__(self, stream: Any = None) -> Any:
+        raise RuntimeError
diff --git a/src/awkward/_nplikes/shape.py b/src/awkward/_nplikes/shape.py
index c7b50c41fe..82493b1b56 100644
--- a/src/awkward/_nplikes/shape.py
+++ b/src/awkward/_nplikes/shape.py
@@ -2,15 +2,20 @@
 from __future__ import annotations
 
 from awkward._singleton import PrivateSingleton
-from awkward._typing import Self, TypeAlias
+from awkward._typing import TYPE_CHECKING, Self, TypeAlias
 
-ShapeItem: TypeAlias = "int | type[unknown_length]"
+__all__ = ("ShapeItem", "UnknownLength", "unknown_length")
 
+ShapeItem: TypeAlias = "int | UnknownLength"
 
-class _UnknownLength(PrivateSingleton):
+if TYPE_CHECKING:
+    from types import NotImplementedType
+
+
+class UnknownLength(PrivateSingleton):
     _instance_name: str
 
-    def __add__(self, other) -> Self | NotImplemented:
+    def __add__(self, other) -> Self | NotImplementedType:
         if isinstance(other, int) or other is self:
             return self
         else:
@@ -19,7 +24,7 @@ def __add__(self, other) -> Self | NotImplemented:
     __radd__ = __add__
     __iadd__ = __add__
 
-    def __sub__(self, other) -> Self | NotImplemented:
+    def __sub__(self, other) -> Self | NotImplementedType:
         if isinstance(other, int) or other is self:
             return self
         else:
@@ -28,7 +33,7 @@ def __sub__(self, other) -> Self | NotImplemented:
     __rsub__ = __sub__
     __isub__ = __sub__
 
-    def __mul__(self, other) -> Self | NotImplemented:
+    def __mul__(self, other) -> Self | NotImplementedType:
         if isinstance(other, int) or other is self:
             return self
         else:
@@ -37,7 +42,7 @@ def __mul__(self, other) -> Self | NotImplemented:
     __rmul__ = __mul__
     __imul__ = __mul__
 
-    def __floordiv__(self, other) -> Self | NotImplemented:
+    def __floordiv__(self, other) -> Self | NotImplementedType:
         if isinstance(other, int) or other is self:
             return self
         else:
@@ -81,7 +86,7 @@ def __int__(self):
 
 
 # Inform the singleton if its module name
-_UnknownLength._instance_name = f"{__name__}.unknown_length"
+UnknownLength._instance_name = f"{__name__}.unknown_length"
 
 # Ensure we have a single instance
-unknown_length = _UnknownLength._new()
+unknown_length = UnknownLength._new()
diff --git a/src/awkward/_nplikes/typetracer.py b/src/awkward/_nplikes/typetracer.py
index 7693cd173c..7bba4d83af 100644
--- a/src/awkward/_nplikes/typetracer.py
+++ b/src/awkward/_nplikes/typetracer.py
@@ -1,6 +1,7 @@
 # BSD 3-Clause License; see https://github.com/scikit-hep/awkward-1.0/blob/main/LICENSE
 from __future__ import annotations
 
+from collections.abc import Sequence
 from numbers import Number
 from typing import Callable
 
@@ -22,14 +23,27 @@
 from awkward._operators import NDArrayOperatorsMixin
 from awkward._regularize import is_integer, is_non_string_like_sequence
 from awkward._typing import (
+    TYPE_CHECKING,
     Any,
+    DType,
     Final,
     Literal,
     Self,
     SupportsIndex,
+    TypeGuard,
     TypeVar,
+    cast,
 )
 
+if TYPE_CHECKING:
+    from types import EllipsisType
+
+    from numpy.typing import DTypeLike
+
+    from awkward.contents.content import Content
+    from awkward.forms.form import Form
+
+
 np = NumpyMetadata.instance()
 NUMPY_HAS_NEP_50 = packaging.version.Version(
     numpy.__version__
@@ -40,15 +54,15 @@ def is_unknown_length(array: Any) -> bool:
     return array is unknown_length
 
 
-def is_unknown_scalar(array: Any) -> bool:
+def is_unknown_scalar(array: Any) -> TypeGuard[TypeTracerArray]:
     return isinstance(array, TypeTracerArray) and array.ndim == 0
 
 
-def is_unknown_integer(array: Any) -> bool:
+def is_unknown_integer(array: Any) -> TypeGuard[TypeTracerArray]:
     return is_unknown_scalar(array) and np.issubdtype(array.dtype, np.integer)
 
 
-def is_unknown_array(array: Any) -> bool:
+def is_unknown_array(array: Any) -> TypeGuard[TypeTracerArray]:
     return isinstance(array, TypeTracerArray) and array.ndim > 0
 
 
@@ -165,7 +179,7 @@ def __reduce__(self):
     @classmethod
     def _new(
         cls,
-        dtype: np.dtype,
+        dtype: DType,
         shape: tuple[ShapeItem, ...],
         form_key: str | None = None,
         report: TypeTracerReport | None = None,
@@ -178,8 +192,10 @@ def _new(
             raise TypeError("typetracer shape must be a tuple")
         if any(is_unknown_scalar(x) for x in shape):
             raise TypeError("typetracer shape must be integers or unknown-length")
+        if not isinstance(dtype, np.dtype):
+            raise TypeError("typetracer dtype must be an instance of np.dtype")
         self._shape = shape
-        self._dtype = np.dtype(dtype)
+        self._dtype = dtype
 
         return self
 
@@ -205,12 +221,12 @@ def T(self) -> Self:
         )
 
     @property
-    def dtype(self) -> np.dtype:
+    def dtype(self) -> DType:
         return self._dtype
 
     @property
     def size(self) -> ShapeItem:
-        size = 1
+        size: ShapeItem = 1
         for item in self._shape:
             size *= item
         return size
@@ -260,7 +276,7 @@ def ndim(self) -> int:
     def nbytes(self) -> ShapeItem:
         return self.size * self._dtype.itemsize
 
-    def view(self, dtype: np.dtype) -> Self:
+    def view(self, dtype: DTypeLike) -> Self:
         dtype = np.dtype(dtype)
         if len(self._shape) >= 1:
             last, remainder = divmod(
@@ -312,10 +328,10 @@ def __getitem__(
         self,
         key: SupportsIndex
         | slice
-        | Ellipsis
-        | tuple[SupportsIndex | slice | Ellipsis | ArrayLike, ...]
+        | EllipsisType
+        | tuple[SupportsIndex | slice | EllipsisType | ArrayLike, ...]
         | ArrayLike,
-    ) -> Self | int | float | bool | complex:
+    ) -> Self:
         if not isinstance(key, tuple):
             key = (key,)
 
@@ -356,7 +372,7 @@ def __getitem__(
             )
 
         # 2. Normalise Ellipsis and boolean arrays
-        key_parts = []
+        key_parts: list[SupportsIndex | slice | ArrayLike] = []
         for item in key:
             if item is Ellipsis:
                 # How many more dimensions do we have than the index provides
@@ -371,9 +387,9 @@ def __getitem__(
         # 3. Apply Indexing
         advanced_is_at_front = False
         previous_item_is_basic = True
-        advanced_shapes = []
-        adjacent_advanced_shape = []
-        result_shape_parts = []
+        advanced_shapes: list[tuple[ShapeItem, ...]] = []
+        adjacent_advanced_shape: list[ShapeItem] = []
+        result_shape_parts: list[Sequence[ShapeItem]] = []
         iter_shape = iter(self.shape)
         for item in key:
             # New axes don't reference existing dimensions
@@ -447,8 +463,8 @@ def __setitem__(
         self,
         key: SupportsIndex
         | slice
-        | Ellipsis
-        | tuple[SupportsIndex | slice | Ellipsis | ArrayLike, ...]
+        | EllipsisType
+        | tuple[SupportsIndex | slice | EllipsisType | ArrayLike, ...]
         | ArrayLike,
         value: int | float | bool | complex | ArrayLike,
     ):
@@ -484,20 +500,26 @@ def __int__(self) -> int:
     def __index__(self) -> int:
         raise RuntimeError("cannot realise an unknown value")
 
+    def __dlpack_device__(self) -> tuple[int, int]:
+        raise RuntimeError("cannot realise an unknown value")
+
+    def __dlpack__(self, stream: Any = None) -> Any:
+        raise RuntimeError("cannot realise an unknown value")
+
 
-def _scalar_type_of(obj) -> numpy.dtype:
+def _scalar_type_of(obj) -> DType:
     if is_unknown_scalar(obj):
         return obj.dtype
     else:
         return numpy.obj2sctype(obj)
 
 
-def try_touch_data(array):
+def try_touch_data(array: Any):
     if isinstance(array, TypeTracerArray):
         array.touch_data()
 
 
-def try_touch_shape(array):
+def try_touch_shape(array: Any):
     if isinstance(array, TypeTracerArray):
         array.touch_shape()
 
@@ -514,9 +536,9 @@ def apply_ufunc(
             self,
             ufunc: UfuncLike,
             method: str,
-            args: list[Any],
+            args: Sequence[Any],
             kwargs: dict[str, Any] | None = None,
-        ) -> TypeTracerArray | tuple[TypeTracerArray]:
+        ) -> TypeTracerArray | tuple[TypeTracerArray, ...]:
             for x in args:
                 try_touch_data(x)
 
@@ -540,7 +562,7 @@ def apply_ufunc(
             if len(result_dtypes) == 1:
                 return TypeTracerArray._new(result_dtypes[0], shape=broadcasted_shape)
             else:
-                return (
+                return tuple(
                     TypeTracerArray._new(dtype, shape=broadcasted_shape)
                     for dtype in result_dtypes
                 )
@@ -551,9 +573,9 @@ def apply_ufunc(
             self,
             ufunc: UfuncLike,
             method: str,
-            args: list[Any],
+            args: Sequence[Any],
             kwargs: dict[str, Any] | None = None,
-        ) -> TypeTracerArray | tuple[TypeTracerArray]:
+        ) -> TypeTracerArray | tuple[TypeTracerArray, ...]:
             for x in args:
                 try_touch_data(x)
 
@@ -561,7 +583,7 @@ def apply_ufunc(
             args = [x.content if isinstance(x, MaybeNone) else x for x in args]
             # Convert np.generic to scalar arrays
             resolved_args = [
-                self.asarray(arg, dtype=arg.dtype) if hasattr(arg, "dtype") else arg
+                self.asarray(arg, dtype=arg.dtype if hasattr(arg, "dtype") else None)
                 for arg in args
             ]
             # Broadcast all inputs together
@@ -569,8 +591,7 @@ def apply_ufunc(
             broadcasted_shape = broadcasted_args[0].shape
             # Choose the broadcasted argument if it wasn't a Python scalar
             non_generic_value_promoted_args = [
-                y if hasattr(x, "ndim") else x
-                for x, y in zip(resolved_args, broadcasted_args)
+                y if hasattr(x, "ndim") else x for x, y in zip(args, broadcasted_args)
             ]
             # Build proxy (empty) arrays
             proxy_args = [
@@ -582,12 +603,13 @@ def apply_ufunc(
             if ufunc.nout == 1:
                 result_dtypes = [proxy_result.dtype]
             else:
+                assert isinstance(proxy_result, tuple)
                 result_dtypes = [x.dtype for x in proxy_result]
 
             if len(result_dtypes) == 1:
                 return TypeTracerArray._new(result_dtypes[0], shape=broadcasted_shape)
             else:
-                return (
+                return tuple(
                     TypeTracerArray._new(dtype, shape=broadcasted_shape)
                     for dtype in result_dtypes
                 )
@@ -615,11 +637,14 @@ def asarray(
         self,
         obj,
         *,
-        dtype: numpy.dtype | None = None,
+        dtype: DTypeLike | None = None,
         copy: bool | None = None,
     ) -> TypeTracerArray:
         assert not isinstance(obj, PlaceholderArray)
 
+        if dtype is not None:
+            dtype = np.dtype(dtype)
+
         if isinstance(obj, ak.index.Index):
             obj = obj.data
 
@@ -663,7 +688,7 @@ def asarray(
                 return TypeTracerArray._new(as_array.dtype, ())
 
             elif is_non_string_like_sequence(obj):
-                shape = []
+                shape: list[ShapeItem] = []
                 flat_items = []
                 has_seen_leaf = False
 
@@ -709,17 +734,17 @@ def populate_shape_and_items(node, dim):
                 raise TypeError
 
     def ascontiguousarray(self, x: ArrayLike) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         return TypeTracerArray._new(
             x.dtype, shape=x.shape, form_key=x.form_key, report=x.report
         )
 
     def frombuffer(
-        self, buffer, *, dtype: np.dtype | None = None, count: int = -1
+        self, buffer, *, dtype: DTypeLike | None = None, count: ShapeItem = -1
     ) -> TypeTracerArray:
-        for x in (buffer, count):
-            assert not isinstance(x, PlaceholderArray)
-            try_touch_data(x)
+        assert not isinstance(buffer, PlaceholderArray)
+        try_touch_data(buffer)
+        try_touch_data(count)
 
         if isinstance(buffer, TypeTracerArray) or is_unknown_scalar(count):
             raise NotImplementedError
@@ -727,29 +752,50 @@ def frombuffer(
             return self.asarray(numpy.frombuffer(buffer, dtype=dtype, count=count))
 
     def from_dlpack(self, x: Any) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         raise NotImplementedError
 
     def zeros(
-        self, shape: ShapeItem | tuple[ShapeItem, ...], *, dtype: np.dtype | None = None
+        self,
+        shape: ShapeItem | tuple[ShapeItem, ...],
+        *,
+        dtype: DTypeLike | None = None,
     ) -> TypeTracerArray:
         if not isinstance(shape, tuple):
             shape = (shape,)
+        if dtype is None:
+            dtype = np.dtype(np.finfo(float).dtype)
+        else:
+            dtype = np.dtype(dtype)
         return TypeTracerArray._new(dtype, shape)
 
     def ones(
-        self, shape: ShapeItem | tuple[ShapeItem, ...], *, dtype: np.dtype | None = None
+        self,
+        shape: ShapeItem | tuple[ShapeItem, ...],
+        *,
+        dtype: DTypeLike | None = None,
     ) -> TypeTracerArray:
         if not isinstance(shape, tuple):
             shape = (shape,)
+        if dtype is None:
+            dtype = np.dtype(np.finfo(float).dtype)
+        else:
+            dtype = np.dtype(dtype)
         return TypeTracerArray._new(dtype, shape)
 
     def empty(
-        self, shape: ShapeItem | tuple[ShapeItem, ...], *, dtype: np.dtype | None = None
+        self,
+        shape: ShapeItem | tuple[ShapeItem, ...],
+        *,
+        dtype: DTypeLike | None = None,
     ) -> TypeTracerArray:
         if not isinstance(shape, tuple):
             shape = (shape,)
+        if dtype is None:
+            dtype = np.dtype(np.finfo(float).dtype)
+        else:
+            dtype = np.dtype(dtype)
         return TypeTracerArray._new(dtype, shape)
 
     def full(
@@ -757,35 +803,39 @@ def full(
         shape: ShapeItem | tuple[ShapeItem, ...],
         fill_value,
         *,
-        dtype: np.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> TypeTracerArray:
         assert not isinstance(fill_value, PlaceholderArray)
         if not isinstance(shape, tuple):
             shape = (shape,)
-        dtype = _scalar_type_of(fill_value) if dtype is None else dtype
+        dtype = _scalar_type_of(fill_value) if dtype is None else np.dtype(dtype)
         return TypeTracerArray._new(dtype, shape)
 
     def zeros_like(
-        self, x: ArrayLike, *, dtype: np.dtype | None = None
+        self, x: ArrayLike, *, dtype: DTypeLike | None = None
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_shape(x)
+        if dtype is None:
+            dtype = x.dtype
+        else:
+            dtype = np.dtype(dtype)
         if is_unknown_scalar(x):
-            return TypeTracerArray._new(dtype or x.dtype, shape=())
+            return TypeTracerArray._new(dtype, shape=())
         else:
-            return TypeTracerArray._new(dtype or x.dtype, shape=x.shape)
+            return TypeTracerArray._new(dtype, shape=x.shape)
 
     def ones_like(
-        self, x: ArrayLike, *, dtype: np.dtype | None = None
+        self, x: ArrayLike, *, dtype: DTypeLike | None = None
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_shape(x)
         return self.zeros_like(x, dtype=dtype)
 
     def full_like(
-        self, x: ArrayLike, fill_value, *, dtype: np.dtype | None = None
+        self, x: ArrayLike, fill_value, *, dtype: DTypeLike | None = None
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_shape(x)
         return self.zeros_like(x, dtype=dtype)
 
@@ -795,7 +845,7 @@ def arange(
         stop: float | int | None = None,
         step: float | int = 1,
         *,
-        dtype: np.dtype | None = None,
+        dtype: DTypeLike | None = None,
     ) -> TypeTracerArray:
         assert not isinstance(start, PlaceholderArray)
         assert not isinstance(stop, PlaceholderArray)
@@ -806,40 +856,40 @@ def arange(
         if stop is None:
             start, stop = 0, start
 
+        length: ShapeItem
         if is_integer(start) and is_integer(stop) and is_integer(step):
-            length = max(0, (stop - start + (step - (1 if step > 0 else -1))) // step)
+            length = max(0, (stop - start + (step - (1 if step > 0 else -1))) // step)  # type: ignore[assignment]
         else:
             length = unknown_length
 
-        default_int_type = np.int32 if (ak._util.win or ak._util.bits32) else np.int64
-        return TypeTracerArray._new(dtype or default_int_type, (length,))
+        if dtype is None:
+            dtype = np.dtype(np.iinfo(int).dtype)
+        else:
+            dtype = np.dtype(dtype)
+        return TypeTracerArray._new(dtype, (length,))
 
     def meshgrid(
         self, *arrays: ArrayLike, indexing: Literal["xy", "ij"] = "xy"
-    ) -> list[TypeTracerArray]:
+    ) -> list[ArrayLike]:
         for x in arrays:
-            assert not isinstance(x, PlaceholderArray)
+            assert isinstance(x, TypeTracerArray)
             try_touch_data(x)
 
             assert x.ndim == 1
 
-        shape = tuple(x.size for x in arrays)
+        shape: list[ShapeItem] = [x.size for x in arrays]
         if indexing == "xy":
             shape[:2] = shape[1], shape[0]
 
         dtype = numpy.result_type(*arrays)
-        return [TypeTracerArray._new(dtype, shape=shape) for _ in arrays]
+        return [TypeTracerArray._new(dtype, shape=tuple(shape)) for _ in arrays]
 
     ############################ testing
 
     def array_equal(
         self, x1: ArrayLike, x2: ArrayLike, *, equal_nan: bool = False
-    ) -> TypeTracerArray:
-        assert not isinstance(x1, PlaceholderArray)
-        assert not isinstance(x2, PlaceholderArray)
-        try_touch_data(x1)
-        try_touch_data(x2)
-        return TypeTracerArray._new(np.bool_, shape=())
+    ) -> bool:
+        raise RuntimeError
 
     def searchsorted(
         self,
@@ -849,7 +899,7 @@ def searchsorted(
         side: Literal["left", "right"] = "left",
         sorter: ArrayLike | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         assert not isinstance(values, PlaceholderArray)
         assert not isinstance(sorter, PlaceholderArray)
         try_touch_data(x)
@@ -870,7 +920,7 @@ def searchsorted(
     ############################ manipulation
     def shape_item_as_index(self, x1: ShapeItem) -> IndexType:
         if x1 is unknown_length:
-            return TypeTracerArray._new(np.int64, shape=())
+            return TypeTracerArray._new(np.dtype(np.int64), shape=())
         elif isinstance(x1, int):
             return x1
         else:
@@ -901,6 +951,7 @@ def regularize_index_for_length(
         if length is unknown_length:
             return length_scalar
 
+        length = cast(int, length)
         # We have known length and index
         if index < 0:
             index = index + length
@@ -1016,9 +1067,9 @@ def broadcast_shapes(self, *shapes: tuple[ShapeItem, ...]) -> tuple[ShapeItem, .
                     )
         return tuple(result)
 
-    def broadcast_arrays(self, *arrays: ArrayLike) -> list[TypeTracerArray]:
+    def broadcast_arrays(self, *arrays: ArrayLike) -> list[ArrayLike]:
         for x in arrays:
-            assert not isinstance(x, PlaceholderArray)
+            assert isinstance(x, TypeTracerArray)
             try_touch_data(x)
 
         if len(arrays) == 0:
@@ -1038,7 +1089,7 @@ def broadcast_arrays(self, *arrays: ArrayLike) -> list[TypeTracerArray]:
     def broadcast_to(
         self, x: ArrayLike, shape: tuple[ShapeItem, ...]
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         new_shape = self.broadcast_shapes(x.shape, shape)
         # broadcast_to is asymmetric, whilst broadcast_shapes is not
@@ -1060,14 +1111,14 @@ def broadcast_to(
     def reshape(
         self, x: ArrayLike, shape: tuple[ShapeItem, ...], *, copy: bool | None = None
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         x.touch_shape()
 
         size = x.size
 
         # Validate new shape to ensure that it only contains at-most one placeholder
         n_placeholders = 0
-        new_size = 1
+        new_size: ShapeItem = 1
         for item in shape:
             if item is unknown_length:
                 # Size is no longer defined
@@ -1103,7 +1154,7 @@ def cumsum(
         axis: int | None = None,
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         if axis is None:
             return TypeTracerArray._new(x.dtype, (x.size,))
@@ -1112,10 +1163,12 @@ def cumsum(
             return TypeTracerArray._new(x.dtype, x.shape)
 
     def nonzero(self, x: ArrayLike) -> tuple[TypeTracerArray, ...]:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         # array
         try_touch_data(x)
-        return (TypeTracerArray._new(np.int64, (unknown_length,)),) * len(x.shape)
+        return (TypeTracerArray._new(np.dtype(np.int64), (unknown_length,)),) * len(
+            x.shape
+        )
 
     def where(
         self, condition: ArrayLike, x1: ArrayLike, x2: ArrayLike
@@ -1128,18 +1181,18 @@ def where(
         return TypeTracerArray._new(result_dtype, shape=condition.shape)
 
     def unique_values(self, x: ArrayLike) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         return TypeTracerArray._new(x.dtype, shape=(unknown_length,))
 
     def unique_all(self, x: ArrayLike) -> UniqueAllResult:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         return UniqueAllResult(
             TypeTracerArray._new(x.dtype, shape=(unknown_length,)),
-            TypeTracerArray._new(np.int64, shape=(unknown_length,)),
-            TypeTracerArray._new(np.int64, shape=x.shape),
-            TypeTracerArray._new(np.int64, shape=(unknown_length,)),
+            TypeTracerArray._new(np.dtype(np.int64), shape=(unknown_length,)),
+            TypeTracerArray._new(np.dtype(np.int64), shape=x.shape),
+            TypeTracerArray._new(np.dtype(np.int64), shape=(unknown_length,)),
         )
 
     def sort(
@@ -1150,7 +1203,7 @@ def sort(
         descending: bool = False,
         stable: bool = True,
     ) -> ArrayLike:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         return TypeTracerArray._new(x.dtype, shape=x.shape)
 
@@ -1165,7 +1218,7 @@ def concat(self, arrays, *, axis: int | None = 0) -> TypeTracerArray:
         inner_shape = None
         emptyarrays = []
         for x in arrays:
-            assert not isinstance(x, PlaceholderArray)
+            assert isinstance(x, TypeTracerArray)
             if inner_shape is None:
                 inner_shape = x.shape[1:]
             elif inner_shape != x.shape[1:]:
@@ -1190,7 +1243,7 @@ def repeat(
         *,
         axis: int | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         assert not isinstance(repeats, PlaceholderArray)
         try_touch_data(x)
         try_touch_data(repeats)
@@ -1217,7 +1270,7 @@ def stack(
         axis: int = 0,
     ) -> TypeTracerArray:
         for x in arrays:
-            assert not isinstance(x, PlaceholderArray)
+            assert isinstance(x, TypeTracerArray)
             try_touch_data(x)
         raise NotImplementedError
 
@@ -1228,7 +1281,7 @@ def packbits(
         axis: int | None = None,
         bitorder: Literal["big", "little"] = "big",
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         raise NotImplementedError
 
@@ -1240,14 +1293,14 @@ def unpackbits(
         count: int | None = None,
         bitorder: Literal["big", "little"] = "big",
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         raise NotImplementedError
 
     def strides(self, x: ArrayLike) -> tuple[ShapeItem, ...]:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         x.touch_shape()
-        out = (x._dtype.itemsize,)
+        out: tuple[ShapeItem, ...] = (x._dtype.itemsize,)
         for item in reversed(x._shape):
             out = (item * out[0], *out)
         return out
@@ -1261,7 +1314,7 @@ def add(
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
         assert not isinstance(x1, PlaceholderArray)
-        return self.apply_ufunc(numpy.add, "__call__", (x1, x2))
+        return self.apply_ufunc(numpy.add, "__call__", (x1, x2))  # type: ignore[arg-type,return-value]
 
     def logical_and(
         self,
@@ -1270,7 +1323,7 @@ def logical_and(
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
         assert not isinstance(x1, PlaceholderArray)
-        return self.apply_ufunc(numpy.logical_and, "__call__", (x1, x2))
+        return self.apply_ufunc(numpy.logical_and, "__call__", (x1, x2))  # type: ignore[arg-type,return-value]
 
     def logical_or(
         self,
@@ -1280,21 +1333,21 @@ def logical_or(
     ) -> TypeTracerArray:
         assert not isinstance(x1, PlaceholderArray)
         assert not isinstance(x2, PlaceholderArray)
-        return self.apply_ufunc(numpy.logical_or, "__call__", (x1, x2))
+        return self.apply_ufunc(numpy.logical_or, "__call__", (x1, x2))  # type: ignore[arg-type,return-value]
 
     def logical_not(
         self, x: ArrayLike, maybe_out: ArrayLike | None = None
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
-        return self.apply_ufunc(numpy.logical_not, "__call__", (x,))
+        assert isinstance(x, TypeTracerArray)
+        return self.apply_ufunc(numpy.logical_not, "__call__", (x,))  # type: ignore[arg-type,return-value]
 
     def sqrt(self, x: ArrayLike, maybe_out: ArrayLike | None = None) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
-        return self.apply_ufunc(numpy.sqrt, "__call__", (x,))
+        assert isinstance(x, TypeTracerArray)
+        return self.apply_ufunc(numpy.sqrt, "__call__", (x,))  # type: ignore[arg-type,return-value]
 
     def exp(self, x: ArrayLike, maybe_out: ArrayLike | None = None) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
-        return self.apply_ufunc(numpy.exp, "__call__", (x,))
+        assert isinstance(x, TypeTracerArray)
+        return self.apply_ufunc(numpy.exp, "__call__", (x,))  # type: ignore[arg-type,return-value]
 
     def divide(
         self,
@@ -1304,7 +1357,7 @@ def divide(
     ) -> TypeTracerArray:
         assert not isinstance(x1, PlaceholderArray)
         assert not isinstance(x2, PlaceholderArray)
-        return self.apply_ufunc(numpy.divide, "__call__", (x1, x2))
+        return self.apply_ufunc(numpy.divide, "__call__", (x1, x2))  # type: ignore[arg-type,return-value]
 
     ############################ almost-ufuncs
 
@@ -1317,7 +1370,7 @@ def nan_to_num(
         posinf: int | float | None = None,
         neginf: int | float | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         return TypeTracerArray._new(x.dtype, shape=x.shape)
 
@@ -1335,12 +1388,12 @@ def isclose(
         try_touch_data(x1)
         try_touch_data(x2)
         out, _ = self.broadcast_arrays(x1, x2)
-        return TypeTracerArray._new(np.bool_, shape=out.shape)
+        return TypeTracerArray._new(np.dtype(np.bool_), shape=out.shape)
 
     def isnan(self, x: ArrayLike) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
-        return TypeTracerArray._new(np.bool_, shape=x.shape)
+        return TypeTracerArray._new(np.dtype(np.bool_), shape=x.shape)
 
     ############################ reducers
 
@@ -1352,10 +1405,10 @@ def all(
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         if axis is None:
-            return TypeTracerArray._new(np.bool_, shape=())
+            return TypeTracerArray._new(np.dtype(np.bool_), shape=())
         else:
             raise NotImplementedError
 
@@ -1367,20 +1420,20 @@ def any(
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         if axis is None:
-            return TypeTracerArray._new(np.bool_, shape=())
+            return TypeTracerArray._new(np.dtype(np.bool_), shape=())
         else:
             raise NotImplementedError
 
     def count_nonzero(
-        self, x: ArrayLike, *, axis: int | None = None
+        self, x: ArrayLike, *, axis: int | tuple[int, ...] | None = None
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         if axis is None:
-            return TypeTracerArray._new(np.intp, shape=())
+            return TypeTracerArray._new(np.dtype(np.intp), shape=())
         else:
             raise NotImplementedError
 
@@ -1392,7 +1445,7 @@ def min(
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         raise NotImplementedError
 
@@ -1404,7 +1457,7 @@ def max(
         keepdims: bool = False,
         maybe_out: ArrayLike | None = None,
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         if axis is None:
             return TypeTracerArray._new(x.dtype, shape=())
@@ -1419,18 +1472,18 @@ def array_str(
         precision: int | None = None,
         suppress_small: bool | None = None,
     ):
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         try_touch_data(x)
         return "[## ... ##]"
 
     def astype(
-        self, x: ArrayLike, dtype: numpy.dtype, *, copy: bool | None = True
+        self, x: ArrayLike, dtype: DTypeLike, *, copy: bool | None = True
     ) -> TypeTracerArray:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         x.touch_data()
         return TypeTracerArray._new(np.dtype(dtype), x.shape)
 
-    def can_cast(self, from_: np.dtype | ArrayLike, to: np.dtype | ArrayLike) -> bool:
+    def can_cast(self, from_: DTypeLike | ArrayLike, to: DTypeLike | ArrayLike) -> bool:
         return numpy.can_cast(from_, to, casting="same_kind")
 
     @classmethod
@@ -1442,7 +1495,7 @@ def is_own_array(cls, obj) -> bool:
         return cls.is_own_array_type(type(obj))
 
     def is_c_contiguous(self, x: ArrayLike) -> bool:
-        assert not isinstance(x, PlaceholderArray)
+        assert isinstance(x, TypeTracerArray)
         return True
 
     def __dlpack_device__(self) -> tuple[int, int]:
@@ -1453,10 +1506,10 @@ def __dlpack__(self, stream=None):
 
 
 def _attach_report(
-    layout: ak.contents.Content,
-    form: ak.forms.Form,
+    layout: Content,
+    form: Form,
     report: TypeTracerReport,
-    getkey: Callable[[ak.forms.form, str], str],
+    getkey: Callable[[Form, str], str],
 ):
     if isinstance(layout, (ak.contents.BitMaskedArray, ak.contents.ByteMaskedArray)):
         assert isinstance(form, (ak.forms.BitMaskedForm, ak.forms.ByteMaskedForm))
@@ -1489,8 +1542,8 @@ def _attach_report(
 
     elif isinstance(layout, ak.contents.NumpyArray):
         assert isinstance(form, ak.forms.NumpyForm)
-        layout.data.form_key = getkey(form, "data")
-        layout.data.report = report
+        layout.data.form_key = getkey(form, "data")  # type: ignore[attr-defined]
+        layout.data.report = report  # type: ignore[attr-defined]
 
     elif isinstance(layout, ak.contents.RecordArray):
         assert isinstance(form, ak.forms.RecordForm)
@@ -1516,7 +1569,7 @@ def _attach_report(
 
 def typetracer_with_report(
     form: ak.forms.Form,
-    getkey: Callable[[ak.forms.form, str], str],
+    getkey: Callable[[Form, str], str],
     forget_length: bool = True,
 ) -> tuple[ak.contents.Content, TypeTracerReport]:
     layout = form.length_zero_array(highlevel=False).to_typetracer(
diff --git a/src/awkward/_typing.py b/src/awkward/_typing.py
index 8a892306d5..286c6ad1a8 100644
--- a/src/awkward/_typing.py
+++ b/src/awkward/_typing.py
@@ -2,11 +2,12 @@
 # ruff: noqa: PLE0604
 from __future__ import annotations
 
-import numpy
 import sys
 import typing
 from typing import *  # noqa: F403
 
+import numpy
+
 __all__ = list(
     {
         "ClassVar",
@@ -16,6 +17,7 @@
         "Protocol",
         "Unpack",
         "TypeAlias",
+        "TypeGuard",
         "runtime_checkable",
         "AxisMaybeNone",
         "TypedDict",
@@ -37,6 +39,7 @@
         Self,
         TypeAlias,
         TypedDict,
+        TypeGuard,
         Unpack,
         final,
     )
@@ -50,6 +53,7 @@
         SupportsIndex,
         TypeAlias,
         TypedDict,
+        TypeGuard,
         Unpack,
         final,
         runtime_checkable,
@@ -61,4 +65,4 @@
 )
 JSONMapping: TypeAlias = "dict[str, JSONSerializable]"
 
-DType = TypeVar("DType", bound=numpy.dtype)
+DType: TypeAlias = numpy.dtype
diff --git a/src/awkward/forms/bitmaskedform.py b/src/awkward/forms/bitmaskedform.py
index c2af2013da..a9a84e68b5 100644
--- a/src/awkward/forms/bitmaskedform.py
+++ b/src/awkward/forms/bitmaskedform.py
@@ -8,9 +8,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import type_parameters_equal
-from awkward._typing import Iterator, JSONSerializable, Self, final
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -209,24 +209,10 @@ def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         if next_content is None:
             return None
         else:
-            return BitMaskedForm(
-                self._mask,
-                next_content,
-                self._valid_when,
-                self._lsb_order,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return BitMaskedForm(
-            self._mask,
-            self._content._select_columns(match_specifier),
-            self._valid_when,
-            self._lsb_order,
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         return self._content._column_types()
@@ -263,7 +249,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "mask"), index_to_dtype[self._mask])
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/bytemaskedform.py b/src/awkward/forms/bytemaskedform.py
index 539fe77518..2e30057b41 100644
--- a/src/awkward/forms/bytemaskedform.py
+++ b/src/awkward/forms/bytemaskedform.py
@@ -7,9 +7,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import type_parameters_equal
-from awkward._typing import Iterator, JSONSerializable, Self, final
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -187,22 +187,10 @@ def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         if next_content is None:
             return None
         else:
-            return ByteMaskedForm(
-                self._mask,
-                next_content,
-                self._valid_when,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return ByteMaskedForm(
-            self._mask,
-            self._content._select_columns(match_specifier),
-            self._valid_when,
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         return self._content._column_types()
@@ -226,7 +214,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "mask"), index_to_dtype[self._mask])
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/emptyform.py b/src/awkward/forms/emptyform.py
index 3ca9622a08..0896ae928a 100644
--- a/src/awkward/forms/emptyform.py
+++ b/src/awkward/forms/emptyform.py
@@ -10,9 +10,9 @@
 from awkward._errors import deprecate
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._nplikes.shape import ShapeItem
-from awkward._typing import Iterator, JSONSerializable, Self, final
-from awkward._util import UNSET
-from awkward.forms.form import Form, JSONMapping
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
+from awkward._util import UNSET, Sentinel
+from awkward.forms.form import Form, JSONMapping, _SpecifierMatcher
 
 np = NumpyMetadata.instance()
 
@@ -22,22 +22,29 @@ class EmptyForm(Form):
     is_numpy = True
     is_unknown = True
 
-    def __init__(self, *, parameters: JSONMapping | None = None, form_key=None):
+    def __init__(
+        self, *, parameters: JSONMapping | None = None, form_key: str | None = None
+    ):
         if not (parameters is None or len(parameters) == 0):
             raise TypeError(f"{type(self).__name__} cannot contain parameters")
         self._init(parameters=parameters, form_key=form_key)
 
     def copy(
-        self, *, parameters: JSONMapping | None = UNSET, form_key=UNSET
+        self,
+        *,
+        parameters: JSONMapping | Sentinel | None = UNSET,
+        form_key: str | Sentinel | None = UNSET,
     ) -> EmptyForm:
-        if not (parameters is UNSET or parameters is None or len(parameters) == 0):
+        if not (parameters is UNSET or parameters is None or len(parameters) == 0):  # type: ignore[arg-type]
             raise TypeError(f"{type(self).__name__} cannot contain parameters")
         return EmptyForm(
-            form_key=self._form_key if form_key is UNSET else form_key,
+            form_key=self._form_key if form_key is UNSET else form_key,  # type: ignore[arg-type]
         )
 
     @classmethod
-    def simplified(cls, *, parameters=None, form_key=None) -> Form:
+    def simplified(
+        cls, *, parameters: JSONMapping | None = None, form_key: str | None = None
+    ) -> Form:
         if not (parameters is None or len(parameters) == 0):
             raise TypeError(f"{cls.__name__} cannot contain parameters")
         return cls(parameters=parameters, form_key=form_key)
@@ -123,7 +130,7 @@ def dimension_optiontype(self) -> bool:
     def _columns(self, path, output, list_indicator):
         output.append(".".join(path))
 
-    def _select_columns(self, match_specifier):
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
         return self
 
     def _prune_columns(self, is_inside_record_or_union: bool) -> Self:
@@ -152,5 +159,5 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield from ()
diff --git a/src/awkward/forms/form.py b/src/awkward/forms/form.py
index 90765d8331..3272e3fd73 100644
--- a/src/awkward/forms/form.py
+++ b/src/awkward/forms/form.py
@@ -17,7 +17,15 @@
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._nplikes.shape import ShapeItem, unknown_length
 from awkward._parameters import parameters_union
-from awkward._typing import Final, Iterator, JSONMapping, JSONSerializable, Self
+from awkward._typing import (
+    ClassVar,
+    DType,
+    Final,
+    Iterator,
+    JSONMapping,
+    JSONSerializable,
+    Self,
+)
 
 np = NumpyMetadata.instance()
 numpy_backend = NumpyBackend.instance()
@@ -328,16 +336,14 @@ def __call__(self, field: str, *, next_match_if_empty: bool = False) -> Self | N
                 next_specifiers.extend(self._match_to_next_specifiers[pattern])
 
         if has_matched:
-            return _SpecifierMatcher(
-                next_specifiers, match_if_empty=next_match_if_empty
-            )
+            return type(self)(next_specifiers, match_if_empty=next_match_if_empty)
         elif self.is_empty and self._match_if_empty:
             return self
         else:
-            return
+            return None
 
 
-def regularize_buffer_key(buffer_key: str | callable) -> Callable[[Form, str], str]:
+def regularize_buffer_key(buffer_key: str | Callable) -> Callable[[Form, str], str]:
     if isinstance(buffer_key, str):
 
         def getkey(form, attribute):
@@ -358,7 +364,7 @@ def getkey(form, attribute):
         )
 
 
-index_to_dtype: Final[dict[str, np.dtype]] = {
+index_to_dtype: Final[dict[str, DType]] = {
     "i8": np.dtype("<i1"),
     "u8": np.dtype("<u1"),
     "i32": np.dtype("<i4"),
@@ -368,16 +374,16 @@ def getkey(form, attribute):
 
 
 class Form:
-    is_numpy = False
-    is_unknown = False
-    is_list = False
-    is_regular = False
-    is_option = False
-    is_indexed = False
-    is_record = False
-    is_union = False
-
-    def _init(self, *, parameters, form_key):
+    is_numpy: ClassVar = False
+    is_unknown: ClassVar = False
+    is_list: ClassVar = False
+    is_regular: ClassVar = False
+    is_option: ClassVar = False
+    is_indexed: ClassVar = False
+    is_record: ClassVar = False
+    is_union: ClassVar = False
+
+    def _init(self, *, parameters: JSONMapping | None, form_key: str | None):
         if parameters is not None and not isinstance(parameters, dict):
             raise TypeError(
                 "{} 'parameters' must be of type dict or None, not {}".format(
@@ -511,6 +517,8 @@ def select_columns(
         specifier = [[] if item == "" else item.split(".") for item in set(specifier)]
         match_specifier = _SpecifierMatcher(specifier, match_if_empty=False)
         selection = self._select_columns(match_specifier)
+        assert selection is not None, "top-level selections always return a Form"
+
         if prune_unions_and_records:
             return selection._prune_columns(False)
         else:
@@ -522,10 +530,10 @@ def column_types(self):
     def _columns(self, path, output, list_indicator):
         raise NotImplementedError
 
-    def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
+    def _prune_columns(self, is_inside_record_or_union: bool) -> Form | None:
         raise NotImplementedError
 
-    def _select_columns(self, match_specifier) -> Self | None:
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Form | None:
         raise NotImplementedError
 
     def _column_types(self):
@@ -658,7 +666,7 @@ def prepare(form, multiplier):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         raise NotImplementedError
 
     def expected_from_buffers(
diff --git a/src/awkward/forms/indexedform.py b/src/awkward/forms/indexedform.py
index 9fd4c6e105..299f9dc30f 100644
--- a/src/awkward/forms/indexedform.py
+++ b/src/awkward/forms/indexedform.py
@@ -8,9 +8,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import parameters_union, type_parameters_equal
-from awkward._typing import Iterator, JSONSerializable, Self, final
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -195,20 +195,10 @@ def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         if next_content is None:
             return None
         else:
-            return IndexedForm(
-                self._index,
-                next_content,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return IndexedForm(
-            self._index,
-            self._content._select_columns(match_specifier),
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         return self._content._column_types()
@@ -230,7 +220,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "index"), index_to_dtype[self._index])
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/indexedoptionform.py b/src/awkward/forms/indexedoptionform.py
index 6eb3ab6eec..1f661315cb 100644
--- a/src/awkward/forms/indexedoptionform.py
+++ b/src/awkward/forms/indexedoptionform.py
@@ -7,9 +7,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import parameters_union, type_parameters_equal
-from awkward._typing import Iterator, JSONSerializable, Self, final
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -176,20 +176,10 @@ def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         if next_content is None:
             return None
         else:
-            return IndexedOptionForm(
-                self._index,
-                next_content,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return IndexedOptionForm(
-            self._index,
-            self._content._select_columns(match_specifier),
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         return self._content._column_types()
@@ -211,7 +201,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "index"), index_to_dtype[self._index])
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/listform.py b/src/awkward/forms/listform.py
index bbeddec7f1..87867d1cc3 100644
--- a/src/awkward/forms/listform.py
+++ b/src/awkward/forms/listform.py
@@ -7,9 +7,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import type_parameters_equal
-from awkward._typing import Iterator, JSONSerializable, final
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -190,27 +190,15 @@ def _columns(self, path, output, list_indicator):
             path = (*path, list_indicator)
         self._content._columns(path, output, list_indicator)
 
-    def _prune_columns(self, is_inside_record_or_union: bool):
+    def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         next_content = self._content._prune_columns(is_inside_record_or_union)
         if next_content is None:
             return None
         else:
-            return ListForm(
-                self._starts,
-                self._stops,
-                next_content,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return ListForm(
-            self._starts,
-            self._stops,
-            self._content._select_columns(match_specifier),
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         if self.parameter("__array__") in ("string", "bytestring"):
@@ -237,7 +225,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "starts"), index_to_dtype[self._starts])
         yield (getkey(self, "stops"), index_to_dtype[self._stops])
         if recursive:
diff --git a/src/awkward/forms/listoffsetform.py b/src/awkward/forms/listoffsetform.py
index 7f6f8214df..4b51859e5a 100644
--- a/src/awkward/forms/listoffsetform.py
+++ b/src/awkward/forms/listoffsetform.py
@@ -8,9 +8,16 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import type_parameters_equal
-from awkward._typing import Iterator, JSONMapping, JSONSerializable, final
+from awkward._typing import (
+    DType,
+    Iterator,
+    JSONMapping,
+    JSONSerializable,
+    Self,
+    final,
+)
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -156,25 +163,15 @@ def _columns(self, path, output, list_indicator):
             path = (*path, list_indicator)
         self._content._columns(path, output, list_indicator)
 
-    def _prune_columns(self, is_inside_record_or_union: bool):
+    def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         next_content = self._content._prune_columns(is_inside_record_or_union)
         if next_content is None:
             return None
         else:
-            return ListOffsetForm(
-                self._offsets,
-                next_content,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return ListOffsetForm(
-            self._offsets,
-            self._content._select_columns(match_specifier),
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         if self.parameter("__array__") in ("string", "bytestring"):
@@ -199,7 +196,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "offsets"), index_to_dtype[self._offsets])
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/numpyform.py b/src/awkward/forms/numpyform.py
index 7e7e3b2564..c41c8762c1 100644
--- a/src/awkward/forms/numpyform.py
+++ b/src/awkward/forms/numpyform.py
@@ -9,14 +9,19 @@
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._nplikes.shape import unknown_length
 from awkward._parameters import type_parameters_equal
-from awkward._typing import JSONSerializable, Self, final
-from awkward._util import UNSET
-from awkward.forms.form import Form
+from awkward._typing import DType, JSONMapping, JSONSerializable, Self, final
+from awkward._util import UNSET, Sentinel
+from awkward.forms.form import Form, _SpecifierMatcher
 
 np = NumpyMetadata.instance()
 
 
-def from_dtype(dtype, parameters=None, *, time_units_as_parameter: bool = UNSET):
+def from_dtype(
+    dtype,
+    parameters: JSONMapping | None = None,
+    *,
+    time_units_as_parameter: bool | Sentinel = UNSET,
+):
     if dtype.subdtype is None:
         inner_shape = ()
     else:
@@ -182,6 +187,7 @@ def purelist_parameters(self, *keys: str) -> JSONSerializable:
             for key in keys:
                 if key in self._parameters:
                     return self._parameters[key]
+        return None
 
     @property
     def purelist_isregular(self):
@@ -219,7 +225,7 @@ def dimension_optiontype(self):
     def _columns(self, path, output, list_indicator):
         output.append(".".join(path))
 
-    def _select_columns(self, match_specifier):
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
         return self
 
     def _prune_columns(self, is_inside_record_or_union: bool) -> Self:
@@ -294,7 +300,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         from awkward.types.numpytype import primitive_to_dtype
 
         yield (getkey(self, "data"), primitive_to_dtype(self.primitive))
diff --git a/src/awkward/forms/recordform.py b/src/awkward/forms/recordform.py
index 26f0f1bc98..67947303c3 100644
--- a/src/awkward/forms/recordform.py
+++ b/src/awkward/forms/recordform.py
@@ -8,10 +8,10 @@
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import type_parameters_equal
 from awkward._regularize import is_integer
-from awkward._typing import JSONSerializable, final
+from awkward._typing import DType, JSONSerializable, Self, final
 from awkward._util import UNSET
 from awkward.errors import FieldNotFoundError
-from awkward.forms.form import Form
+from awkward.forms.form import Form, _SpecifierMatcher
 
 np = NumpyMetadata.instance()
 
@@ -198,6 +198,7 @@ def purelist_parameters(self, *keys: str) -> JSONSerializable:
             for key in keys:
                 if key in self._parameters:
                     return self._parameters[key]
+        return None
 
     @property
     def purelist_isregular(self):
@@ -246,7 +247,7 @@ def _columns(self, path, output, list_indicator):
         for content, field in zip(self._contents, self.fields):
             content._columns((*path, field), output, list_indicator)
 
-    def _prune_columns(self, is_inside_record_or_union: bool):
+    def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         contents = []
         fields = []
         for content, field in zip(self._contents, self.fields):
@@ -256,18 +257,13 @@ def _prune_columns(self, is_inside_record_or_union: bool):
             contents.append(next_content)
             fields.append(field)
 
-        if fields or not is_inside_record_or_union:
-            return RecordForm(
-                contents,
-                fields,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
         # If all subtrees are pruned (or we have no subtrees!), then we should prune this form too
-        else:
+        if not fields and is_inside_record_or_union:
             return None
+        else:
+            return self.copy(contents=contents, fields=fields)
 
-    def _select_columns(self, match_specifier):
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
         contents = []
         fields = []
         for content, field in zip(self._contents, self.fields):
@@ -283,12 +279,7 @@ def _select_columns(self, match_specifier):
             contents.append(next_content)
             fields.append(field)
 
-        return RecordForm(
-            contents,
-            fields,
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+        return self.copy(contents=contents, fields=fields)
 
     def _column_types(self):
         return sum((x._column_types() for x in self._contents), ())
@@ -312,7 +303,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         if recursive:
             for content in self._contents:
                 yield from content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/regularform.py b/src/awkward/forms/regularform.py
index 9f82666a56..974a579783 100644
--- a/src/awkward/forms/regularform.py
+++ b/src/awkward/forms/regularform.py
@@ -9,9 +9,9 @@
 from awkward._nplikes.shape import unknown_length
 from awkward._parameters import type_parameters_equal
 from awkward._regularize import is_integer
-from awkward._typing import JSONSerializable, final
+from awkward._typing import DType, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form
+from awkward.forms.form import Form, _SpecifierMatcher
 
 np = NumpyMetadata.instance()
 
@@ -151,25 +151,15 @@ def _columns(self, path, output, list_indicator):
             path = (*path, list_indicator)
         self._content._columns(path, output, list_indicator)
 
-    def _prune_columns(self, is_inside_record_or_union: bool):
+    def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         next_content = self._content._prune_columns(is_inside_record_or_union)
         if next_content is None:
             return None
         else:
-            return RegularForm(
-                next_content,
-                self._size,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return RegularForm(
-            self._content._select_columns(match_specifier),
-            self._size,
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         if self.parameter("__array__") in ("string", "bytestring"):
@@ -194,6 +184,6 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)
diff --git a/src/awkward/forms/unionform.py b/src/awkward/forms/unionform.py
index 8ad5c577da..fca998a679 100644
--- a/src/awkward/forms/unionform.py
+++ b/src/awkward/forms/unionform.py
@@ -8,9 +8,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import type_parameters_equal
-from awkward._typing import Iterator, JSONSerializable, Self, final
+from awkward._typing import DType, Iterator, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form, index_to_dtype
+from awkward.forms.form import Form, _SpecifierMatcher, index_to_dtype
 
 np = NumpyMetadata.instance()
 
@@ -168,6 +168,8 @@ def purelist_parameters(self, *keys: str) -> JSONSerializable:
                     return None
             return out
 
+        return None
+
     @property
     def purelist_isregular(self):
         for content in self._contents:
@@ -236,7 +238,7 @@ def _columns(self, path, output, list_indicator):
         for content, field in zip(self._contents, self.fields):
             content._columns((*path, field), output, list_indicator)
 
-    def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
+    def _prune_columns(self, is_inside_record_or_union: bool) -> Form | None:
         contents = []
         for content in self._contents:
             next_content = content._prune_columns(True)
@@ -253,26 +255,14 @@ def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         elif len(contents) == 1:
             return contents[0]
         else:
-            return UnionForm(
-                self._tags,
-                self._index,
-                contents,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(contents=contents)
 
-    def _select_columns(self, match_specifier):
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
         contents = [
             content._select_columns(match_specifier) for content in self._contents
         ]
 
-        return UnionForm(
-            self._tags,
-            self._index,
-            contents,
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+        return self.copy(contents=contents)
 
     def _column_types(self):
         return sum((x._column_types() for x in self._contents), ())
@@ -296,7 +286,7 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         yield (getkey(self, "tags"), index_to_dtype[self._tags])
         yield (getkey(self, "index"), index_to_dtype[self._index])
         if recursive:
diff --git a/src/awkward/forms/unmaskedform.py b/src/awkward/forms/unmaskedform.py
index c6ea768e9d..722885f6fb 100644
--- a/src/awkward/forms/unmaskedform.py
+++ b/src/awkward/forms/unmaskedform.py
@@ -7,9 +7,9 @@
 import awkward as ak
 from awkward._nplikes.numpylike import NumpyMetadata
 from awkward._parameters import parameters_union, type_parameters_equal
-from awkward._typing import JSONSerializable, Self, final
+from awkward._typing import DType, JSONSerializable, Self, final
 from awkward._util import UNSET
-from awkward.forms.form import Form
+from awkward.forms.form import Form, _SpecifierMatcher
 
 np = NumpyMetadata.instance()
 
@@ -150,18 +150,10 @@ def _prune_columns(self, is_inside_record_or_union: bool) -> Self | None:
         if next_content is None:
             return None
         else:
-            return UnmaskedForm(
-                next_content,
-                parameters=self._parameters,
-                form_key=self._form_key,
-            )
+            return self.copy(content=next_content)
 
-    def _select_columns(self, match_specifier):
-        return UnmaskedForm(
-            self._content._select_columns(match_specifier),
-            parameters=self._parameters,
-            form_key=self._form_key,
-        )
+    def _select_columns(self, match_specifier: _SpecifierMatcher) -> Self:
+        return self.copy(content=self._content._select_columns(match_specifier))
 
     def _column_types(self):
         return self._content._column_types()
@@ -183,6 +175,6 @@ def __setstate__(self, state):
 
     def _expected_from_buffers(
         self, getkey: Callable[[Form, str], str], recursive: bool
-    ) -> Iterator[tuple[str, np.dtype]]:
+    ) -> Iterator[tuple[str, DType]]:
         if recursive:
             yield from self._content._expected_from_buffers(getkey, recursive)