diff --git a/docs/api.rst b/docs/api.rst
index e8aa1801f..74700063d 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -38,4 +38,4 @@ Data
 ----
 
 .. automodule:: sphinx_needs.data
-   :members: NeedsInfoType, NeedsView
+   :members: NeedsInfoType, NeedsMutable, NeedsView
diff --git a/docs/conf.py b/docs/conf.py
index 2913a542b..527bcecda 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -756,7 +756,7 @@ def create_tutorial_needs(app: Sphinx, _env, _docnames):
 
     We do this dynamically, to avoid having to maintain the JSON file manually.
     """
-    all_data = SphinxNeedsData(app.env).get_needs_view()
+    all_data = SphinxNeedsData(app.env).get_needs_mutable()
     writer = NeedsList(app.config, outdir=app.confdir, confdir=app.confdir)
     for i in range(1, 5):
         test_id = f"T_00{i}"
diff --git a/sphinx_needs/api/__init__.py b/sphinx_needs/api/__init__.py
index 6021aedec..1601cf1d6 100644
--- a/sphinx_needs/api/__init__.py
+++ b/sphinx_needs/api/__init__.py
@@ -4,7 +4,7 @@
     add_need_type,
     get_need_types,
 )
-from .need import add_external_need, add_need, del_need, make_hashed_id
+from .need import add_external_need, add_need, del_need, get_needs_view, make_hashed_id
 
 __all__ = (
     "add_dynamic_function",
@@ -14,5 +14,6 @@
     "add_need_type",
     "del_need",
     "get_need_types",
+    "get_needs_view",
     "make_hashed_id",
 )
diff --git a/sphinx_needs/api/need.py b/sphinx_needs/api/need.py
index b734c4cf5..3eaba290d 100644
--- a/sphinx_needs/api/need.py
+++ b/sphinx_needs/api/need.py
@@ -24,7 +24,7 @@
     NeedsTemplateException,
 )
 from sphinx_needs.config import NEEDS_CONFIG, GlobalOptionsType, NeedsSphinxConfig
-from sphinx_needs.data import NeedsInfoType, SphinxNeedsData
+from sphinx_needs.data import NeedsInfoType, NeedsView, SphinxNeedsData
 from sphinx_needs.directives.needuml import Needuml, NeedumlException
 from sphinx_needs.filter_common import filter_single_need
 from sphinx_needs.logging import get_logger, log_warning
@@ -805,3 +805,15 @@ def _merge_global_options(
                 # has at least the key.
                 if key not in needs_info.keys():
                     needs_info[key] = ""
+
+
+def get_needs_view(app: Sphinx) -> NeedsView:
+    """Return a read-only view of all resolved needs.
+
+    .. important:: this should only be called within the write phase,
+        after the needs have been fully collected.
+        If not already done, this will ensure all needs are resolved
+        (e.g. back links have been computed etc),
+        and then lock the data to prevent further modification.
+    """
+    return SphinxNeedsData(app.env).get_needs_view()
diff --git a/sphinx_needs/builder.py b/sphinx_needs/builder.py
index ad026c130..9acbd179b 100644
--- a/sphinx_needs/builder.py
+++ b/sphinx_needs/builder.py
@@ -9,8 +9,6 @@
 
 from sphinx_needs.config import NeedsSphinxConfig
 from sphinx_needs.data import SphinxNeedsData
-from sphinx_needs.directives.need import post_process_needs_data
-from sphinx_needs.filter_common import filter_needs_view
 from sphinx_needs.logging import get_logger, log_warning
 from sphinx_needs.needsfile import NeedsList
 
@@ -58,9 +56,10 @@ def write(
         return super().write(build_docnames, updated_docnames, method)
 
     def finish(self) -> None:
-        post_process_needs_data(self.app)
+        from sphinx_needs.filter_common import filter_needs_view
 
         data = SphinxNeedsData(self.env)
+        needs = data.get_needs_view()
         needs_config = NeedsSphinxConfig(self.env.config)
         filters = data.get_or_create_filters()
         version = getattr(self.env.config, "version", "unset")
@@ -84,7 +83,7 @@ def finish(self) -> None:
 
         filter_string = needs_config.builder_filter
         filtered_needs = filter_needs_view(
-            data.get_needs_view(),
+            needs,
             needs_config,
             filter_string,
             append_warning="(from need_builder_filter)",
@@ -173,7 +172,7 @@ def write(
         pass
 
     def finish(self) -> None:
-        post_process_needs_data(self.app)
+        from sphinx_needs.filter_common import filter_needs_view
 
         data = SphinxNeedsData(self.env)
         version = getattr(self.env.config, "version", "unset")
diff --git a/sphinx_needs/data.py b/sphinx_needs/data.py
index a61eb1430..c52f9cec2 100644
--- a/sphinx_needs/data.py
+++ b/sphinx_needs/data.py
@@ -730,6 +730,8 @@ def add_need(self, need: NeedsInfoType) -> None:
         .. important:: this should only be called within the read phase,
             before the needs have been fully collected and resolved.
         """
+        if self.needs_is_post_processed:
+            raise RuntimeError("Needs have already been post-processed.")
         self._env_needs[need["id"]] = need
 
     def remove_need(self, need_id: str) -> None:
@@ -738,6 +740,8 @@ def remove_need(self, need_id: str) -> None:
         .. important:: this should only be called within the read phase,
             before the needs have been fully collected and resolved.
         """
+        if self.needs_is_post_processed:
+            raise RuntimeError("Needs have already been post-processed.")
         if need_id in self._env_needs:
             del self._env_needs[need_id]
         self.remove_need_node(need_id)
@@ -748,6 +752,8 @@ def remove_doc(self, docname: str) -> None:
         .. important:: this should only be called within the read phase,
             before the needs have been fully collected and resolved.
         """
+        if self.needs_is_post_processed:
+            raise RuntimeError("Needs have already been post-processed.")
         for need_id in list(self._env_needs):
             if self._env_needs[need_id]["docname"] == docname:
                 del self._env_needs[need_id]
@@ -762,15 +768,23 @@ def get_needs_mutable(self) -> NeedsMutable:
         .. important:: this should only be called within the read phase,
             before the needs have been fully collected and resolved.
         """
+        if self.needs_is_post_processed:
+            raise RuntimeError("Needs have already been post-processed.")
         return self._env_needs  # type: ignore[return-value]
 
     def get_needs_view(self) -> NeedsView:
-        """Return a read-only view of all needs, after resolution.
+        """Return a read-only view of all resolved needs.
 
         .. important:: this should only be called within the write phase,
-            after the needs have been fully collected
-            and resolved (e.g. back links have been computed etc)
+            after the needs have been fully collected.
+            If not already done, this will ensure all needs are resolved
+            (e.g. back links have been computed etc),
+            and then lock the data to prevent further modification.
         """
+        if not self.needs_is_post_processed:
+            from sphinx_needs.directives.need import post_process_needs_data
+
+            post_process_needs_data(self.env.app)
         return self._env_needs  # type: ignore[return-value]
 
     @property
diff --git a/sphinx_needs/directives/need.py b/sphinx_needs/directives/need.py
index 6ad096a57..2b1c587e7 100644
--- a/sphinx_needs/directives/need.py
+++ b/sphinx_needs/directives/need.py
@@ -373,10 +373,10 @@ def post_process_needs_data(app: Sphinx) -> None:
     After this function has been run, one should assume that the needs data is finalised,
     and so in principle should be treated as read-only.
     """
-    needs_config = NeedsSphinxConfig(app.config)
     needs_data = SphinxNeedsData(app.env)
-    needs = needs_data.get_needs_mutable()
-    if needs and not needs_data.needs_is_post_processed:
+    if not needs_data.needs_is_post_processed:
+        needs_config = NeedsSphinxConfig(app.config)
+        needs = needs_data.get_needs_mutable()
         extend_needs_data(needs, needs_data.get_or_create_extends(), needs_config)
         resolve_dynamic_values(needs, app)
         resolve_variants_options(needs, needs_config, app.builder.tags)
@@ -404,8 +404,6 @@ def process_need_nodes(app: Sphinx, doctree: nodes.document, fromdocname: str) -
     if not needs_data.get_needs_view():
         return
 
-    post_process_needs_data(app)
-
     for extend_node in list(doctree.findall(Needextend)):
         remove_node_from_tree(extend_node)
 
diff --git a/sphinx_needs/external_needs.py b/sphinx_needs/external_needs.py
index 5182adaa1..7a596ac1a 100644
--- a/sphinx_needs/external_needs.py
+++ b/sphinx_needs/external_needs.py
@@ -167,7 +167,7 @@ def load_external_needs(app: Sphinx, env: BuildEnvironment, docname: str) -> Non
             # check if external needs already exist
             ext_need_id = need_params["id"]
 
-            need = SphinxNeedsData(env).get_needs_view().get(ext_need_id)
+            need = SphinxNeedsData(env).get_needs_mutable().get(ext_need_id)
 
             if need is not None:
                 # check need_params for more detail
diff --git a/sphinx_needs/functions/common.py b/sphinx_needs/functions/common.py
index 105d21565..b2d48ba2b 100644
--- a/sphinx_needs/functions/common.py
+++ b/sphinx_needs/functions/common.py
@@ -14,9 +14,9 @@
 
 from sphinx_needs.api.exceptions import NeedsInvalidFilter
 from sphinx_needs.config import NeedsSphinxConfig
-from sphinx_needs.data import NeedsInfoType, NeedsView
+from sphinx_needs.data import NeedsInfoType, NeedsMutable, NeedsView
 from sphinx_needs.filter_common import (
-    filter_needs_view,
+    filter_needs,
     filter_single_need,
 )
 from sphinx_needs.logging import log_warning
@@ -26,7 +26,7 @@
 def test(
     app: Sphinx,
     need: NeedsInfoType | None,
-    needs: NeedsView,
+    needs: NeedsMutable | NeedsView,
     *args: Any,
     **kwargs: Any,
 ) -> str:
@@ -54,7 +54,7 @@ def test(
 def echo(
     app: Sphinx,
     need: NeedsInfoType | None,
-    needs: NeedsView,
+    needs: NeedsMutable | NeedsView,
     text: str,
     *args: Any,
     **kwargs: Any,
@@ -78,7 +78,7 @@ def echo(
 def copy(
     app: Sphinx,
     need: NeedsInfoType | None,
-    needs: NeedsView,
+    needs: NeedsMutable | NeedsView,
     option: str,
     need_id: str | None = None,
     lower: bool = False,
@@ -170,14 +170,15 @@ def copy(
         need = needs[need_id]
 
     if filter:
-        result = filter_needs_view(
-            needs,
+        location = (
+            (need["docname"], need["lineno"]) if need and need["docname"] else None
+        )
+        result = filter_needs(
+            needs.values(),
             NeedsSphinxConfig(app.config),
             filter,
             need,
-            location=(need["docname"], need["lineno"])
-            if need and need["docname"]
-            else None,
+            location=location,
         )
         if result:
             need = result[0]
@@ -201,7 +202,7 @@ def copy(
 def check_linked_values(
     app: Sphinx,
     need: NeedsInfoType | None,
-    needs: NeedsView,
+    needs: NeedsMutable | NeedsView,
     result: Any,
     search_option: str,
     search_value: Any,
@@ -373,7 +374,7 @@ def check_linked_values(
 def calc_sum(
     app: Sphinx,
     need: NeedsInfoType | None,
-    needs: NeedsView,
+    needs: NeedsMutable | NeedsView,
     option: str,
     filter: str | None = None,
     links_only: bool = False,
@@ -488,7 +489,7 @@ def calc_sum(
 def links_from_content(
     app: Sphinx,
     need: NeedsInfoType | None,
-    needs: NeedsView,
+    needs: NeedsMutable | NeedsView,
     need_id: str | None = None,
     filter: str | None = None,
 ) -> list[str]:
diff --git a/sphinx_needs/functions/functions.py b/sphinx_needs/functions/functions.py
index a849e87cb..c15708c37 100644
--- a/sphinx_needs/functions/functions.py
+++ b/sphinx_needs/functions/functions.py
@@ -40,7 +40,7 @@ def __call__(
         self,
         app: Sphinx,
         need: NeedsInfoType | None,
-        needs: NeedsView,
+        needs: NeedsView | NeedsMutable,
         *args: Any,
         **kwargs: Any,
     ) -> str | int | float | list[str] | list[int] | list[float] | None: ...
@@ -78,6 +78,7 @@ def register_func(need_function: DynamicFunction, name: str | None = None) -> No
 def execute_func(
     app: Sphinx,
     need: NeedsInfoType | None,
+    needs: NeedsView | NeedsMutable,
     func_string: str,
     location: str | tuple[str | None, int | None] | nodes.Node | None,
 ) -> str | int | float | list[str] | list[int] | list[float] | None:
@@ -118,7 +119,7 @@ def execute_func(
         func_return = func(
             app,
             need,
-            SphinxNeedsData(app.env).get_needs_view(),
+            needs,
             *func_args,
             **func_kwargs,
         )
@@ -201,7 +202,9 @@ def find_and_replace_node_content(
             msg = f"The [[{func_string}]] syntax in need content is deprecated. Replace with :ndf:`{func_string}` instead."
             log_warning(logger, msg, "deprecation", location=node)
 
-            func_return = execute_func(env.app, need, func_string, node)
+            func_return = execute_func(
+                env.app, need, SphinxNeedsData(env).get_needs_view(), func_string, node
+            )
 
             if isinstance(func_return, list):
                 func_return = ", ".join(str(el) for el in func_return)
@@ -266,7 +269,7 @@ def resolve_dynamic_values(needs: NeedsMutable, app: Sphinx) -> None:
                 while func_call:
                     try:
                         func_call, func_return = _detect_and_execute_field(
-                            need[need_option], need, app
+                            need[need_option], need, needs, app
                         )
                     except FunctionParsingException:
                         raise SphinxError(
@@ -298,7 +301,7 @@ def resolve_dynamic_values(needs: NeedsMutable, app: Sphinx) -> None:
                 for element in need[need_option]:
                     try:
                         func_call, func_return = _detect_and_execute_field(
-                            element, need, app
+                            element, need, needs, app
                         )
                     except FunctionParsingException:
                         raise SphinxError(
@@ -401,7 +404,7 @@ def check_and_get_content(
 
     func_call = func_match.group(1)  # Extract function call
     func_return = execute_func(
-        env.app, need, func_call, location
+        env.app, need, SphinxNeedsData(env).get_needs_view(), func_call, location
     )  # Execute function call and get return value
 
     if isinstance(func_return, list):
@@ -415,13 +418,10 @@ def check_and_get_content(
 
 
 def _detect_and_execute_field(
-    content: Any, need: NeedsInfoType, app: Sphinx
+    content: Any, need: NeedsInfoType, needs: NeedsMutable, app: Sphinx
 ) -> tuple[str | None, str | int | float | list[str] | list[int] | list[float] | None]:
     """Detects if given need field value is a function call and executes it."""
-    try:
-        content = str(content)
-    except UnicodeEncodeError:
-        content = content.encode("utf-8")
+    content = str(content)
 
     func_match = FUNC_RE.search(content)
     if func_match is None:
@@ -431,6 +431,7 @@ def _detect_and_execute_field(
     func_return = execute_func(
         app,
         need,
+        needs,
         func_call,
         (need["docname"], need["lineno"]) if need["docname"] else None,
     )  # Execute function call and get return value
diff --git a/sphinx_needs/needs.py b/sphinx_needs/needs.py
index 44051b063..5ce24aa32 100644
--- a/sphinx_needs/needs.py
+++ b/sphinx_needs/needs.py
@@ -503,7 +503,6 @@ def prepare_env(app: Sphinx, env: BuildEnvironment, _docname: str) -> None:
     """
     needs_config = NeedsSphinxConfig(app.config)
     data = SphinxNeedsData(env)
-    data.get_needs_view()
     data.get_or_create_filters()
     data.get_or_create_docs()
     services = data.get_or_create_services()
diff --git a/sphinx_needs/roles/need_func.py b/sphinx_needs/roles/need_func.py
index 309f883d3..d5d09ae13 100644
--- a/sphinx_needs/roles/need_func.py
+++ b/sphinx_needs/roles/need_func.py
@@ -9,7 +9,7 @@
 from sphinx.environment import BuildEnvironment
 from sphinx.util.docutils import SphinxRole
 
-from sphinx_needs.data import NeedsInfoType
+from sphinx_needs.data import NeedsInfoType, SphinxNeedsData
 from sphinx_needs.logging import get_logger, log_warning
 from sphinx_needs.utils import add_doc
 
@@ -60,7 +60,13 @@ def get_text(self, env: BuildEnvironment, need: NeedsInfoType | None) -> nodes.T
         from sphinx_needs.functions.functions import check_and_get_content, execute_func
 
         if not self.with_brackets:
-            func_return = execute_func(env.app, need, self.astext(), self)
+            func_return = execute_func(
+                env.app,
+                need,
+                SphinxNeedsData(env).get_needs_view(),
+                self.astext(),
+                self,
+            )
             if isinstance(func_return, list):
                 func_return = ", ".join(str(el) for el in func_return)