diff --git a/rosidl_cli/package.xml b/rosidl_cli/package.xml
index 46f5c7ee5..e45804c7a 100644
--- a/rosidl_cli/package.xml
+++ b/rosidl_cli/package.xml
@@ -22,6 +22,7 @@
 
   <test_depend>ament_copyright</test_depend>
   <test_depend>ament_flake8</test_depend>
+  <test_depend>ament_mypy</test_depend>
   <test_depend>ament_pep257</test_depend>
   <test_depend>ament_xmllint</test_depend>
   <test_depend>python3-pytest</test_depend>
diff --git a/rosidl_cli/py.typed b/rosidl_cli/py.typed
new file mode 100644
index 000000000..e69de29bb
diff --git a/rosidl_cli/rosidl_cli/cli.py b/rosidl_cli/rosidl_cli/cli.py
index 9c3f8ac28..ce729a816 100644
--- a/rosidl_cli/rosidl_cli/cli.py
+++ b/rosidl_cli/rosidl_cli/cli.py
@@ -14,13 +14,18 @@
 
 import argparse
 import signal
+from typing import Any, List, Union
 
 from rosidl_cli.command.generate import GenerateCommand
 from rosidl_cli.command.translate import TranslateCommand
 from rosidl_cli.common import get_first_line_doc
 
 
-def add_subparsers(parser, cli_name, commands):
+def add_subparsers(
+    parser: argparse.ArgumentParser,
+    cli_name: str,
+    commands: List[Union[GenerateCommand, TranslateCommand]]
+) -> argparse._SubParsersAction[argparse.ArgumentParser]:
     """
     Create argparse subparser for each command.
 
@@ -63,7 +68,7 @@ def add_subparsers(parser, cli_name, commands):
     return subparser
 
 
-def main():
+def main() -> Union[str, signal.Signals, Any]:
     script_name = 'rosidl'
     description = f'{script_name} is an extensible command-line tool ' \
         'for ROS interface generation.'
@@ -74,7 +79,8 @@ def main():
         formatter_class=argparse.RawDescriptionHelpFormatter
     )
 
-    commands = [GenerateCommand(), TranslateCommand()]
+    commands: List[Union[GenerateCommand, TranslateCommand]] = \
+        [GenerateCommand(), TranslateCommand()]
 
     # add arguments for command extension(s)
     add_subparsers(
diff --git a/rosidl_cli/rosidl_cli/command/__init__.py b/rosidl_cli/rosidl_cli/command/__init__.py
index 22d035bb5..187a6c187 100644
--- a/rosidl_cli/rosidl_cli/command/__init__.py
+++ b/rosidl_cli/rosidl_cli/command/__init__.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
+
 
 class Command:
     """
@@ -22,8 +24,8 @@ class Command:
     * `add_arguments`
     """
 
-    def add_arguments(self, parser):
+    def add_arguments(self, parser: argparse.ArgumentParser) -> None:
         pass
 
-    def main(self, *, parser, args):
+    def main(self, *, args: argparse.Namespace) -> None:
         raise NotImplementedError()
diff --git a/rosidl_cli/rosidl_cli/command/generate/__init__.py b/rosidl_cli/rosidl_cli/command/generate/__init__.py
index ee46a937a..b12b946c1 100644
--- a/rosidl_cli/rosidl_cli/command/generate/__init__.py
+++ b/rosidl_cli/rosidl_cli/command/generate/__init__.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
 import pathlib
 
 from rosidl_cli.command import Command
@@ -24,7 +25,7 @@ class GenerateCommand(Command):
 
     name = 'generate'
 
-    def add_arguments(self, parser):
+    def add_arguments(self, parser: argparse.ArgumentParser) -> None:
         parser.add_argument(
             '-o', '--output-path', metavar='PATH',
             type=pathlib.Path, default=None,
@@ -50,7 +51,7 @@ def add_arguments(self, parser):
                   "If prefixed by another path followed by a colon ':', "
                   'path resolution is performed against such path.'))
 
-    def main(self, *, args):
+    def main(self, *, args: argparse.Namespace) -> None:
         generate(
             package_name=args.package_name,
             interface_files=args.interface_files,
diff --git a/rosidl_cli/rosidl_cli/command/generate/api.py b/rosidl_cli/rosidl_cli/command/generate/api.py
index ebec89144..ff7edbbcb 100644
--- a/rosidl_cli/rosidl_cli/command/generate/api.py
+++ b/rosidl_cli/rosidl_cli/command/generate/api.py
@@ -14,20 +14,22 @@
 
 import os
 import pathlib
+from typing import List, Optional
 
+from .extensions import GenerateCommandExtension
 from .extensions import load_type_extensions
 from .extensions import load_typesupport_extensions
 
 
 def generate(
     *,
-    package_name,
-    interface_files,
-    include_paths=None,
-    output_path=None,
-    types=None,
-    typesupports=None
-):
+    package_name: str,
+    interface_files: List[str],
+    include_paths: Optional[List[str]] = None,
+    output_path: Optional[pathlib.Path] = None,
+    types: Optional[List[str]] = None,
+    typesupports: Optional[List[str]] = None
+) -> List[List[str]]:
     """
     Generate source code from interface definition files.
 
@@ -60,7 +62,7 @@ def generate(
     :returns: list of lists of paths to generated source code files,
         one group per type or type support extension invoked
     """
-    extensions = []
+    extensions: List[GenerateCommandExtension] = []
 
     unspecific_generation = not types and not typesupports
 
diff --git a/rosidl_cli/rosidl_cli/command/generate/extensions.py b/rosidl_cli/rosidl_cli/command/generate/extensions.py
index fde1fb6b0..a89630d71 100644
--- a/rosidl_cli/rosidl_cli/command/generate/extensions.py
+++ b/rosidl_cli/rosidl_cli/command/generate/extensions.py
@@ -12,6 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from pathlib import Path
+from typing import cast, List, Optional
+
 from rosidl_cli.extensions import Extension
 from rosidl_cli.extensions import load_extensions
 
@@ -26,11 +29,11 @@ class GenerateCommandExtension(Extension):
 
     def generate(
         self,
-        package_name,
-        interface_files,
-        include_paths,
-        output_path
-    ):
+        package_name: str,
+        interface_files: List[str],
+        include_paths: List[str],
+        output_path: Path
+    ) -> List[str]:
         """
         Generate source code.
 
@@ -48,11 +51,17 @@ def generate(
         raise NotImplementedError()
 
 
-def load_type_extensions(**kwargs):
+def load_type_extensions(*, specs: Optional[List[str]],
+                         strict: bool) -> List[GenerateCommandExtension]:
     """Load extensions for type representation source code generation."""
-    return load_extensions('rosidl_cli.command.generate.type_extensions', **kwargs)
+    extensions = load_extensions('rosidl_cli.command.generate.type_extensions', specs=specs,
+                                 strict=strict)
+    return cast(List[GenerateCommandExtension], extensions)
 
 
-def load_typesupport_extensions(**kwargs):
+def load_typesupport_extensions(*, specs: Optional[List[str]], strict: bool
+                                ) -> List[GenerateCommandExtension]:
     """Load extensions for type support source code generation."""
-    return load_extensions('rosidl_cli.command.generate.typesupport_extensions', **kwargs)
+    extensions = load_extensions('rosidl_cli.command.generate.typesupport_extensions',
+                                 specs=specs, strict=strict)
+    return cast(List[GenerateCommandExtension], extensions)
diff --git a/rosidl_cli/rosidl_cli/command/helpers.py b/rosidl_cli/rosidl_cli/command/helpers.py
index f23cc9a88..d81b0cdc3 100644
--- a/rosidl_cli/rosidl_cli/command/helpers.py
+++ b/rosidl_cli/rosidl_cli/command/helpers.py
@@ -17,9 +17,10 @@
 import os
 import pathlib
 import tempfile
+from typing import Generator, List, Tuple
 
 
-def package_name_from_interface_file_path(path):
+def package_name_from_interface_file_path(path: pathlib.Path) -> str:
     """
     Derive ROS package name from a ROS interface definition file path.
 
@@ -29,7 +30,7 @@ def package_name_from_interface_file_path(path):
     return pathlib.Path(os.path.abspath(path)).parents[1].name
 
 
-def dependencies_from_include_paths(include_paths):
+def dependencies_from_include_paths(include_paths: List[str]) -> List[str]:
     """
     Collect dependencies' ROS interface definition files from include paths.
 
@@ -45,7 +46,7 @@ def dependencies_from_include_paths(include_paths):
     })
 
 
-def interface_path_as_tuple(path):
+def interface_path_as_tuple(path: str) -> Tuple[pathlib.Path, pathlib.Path]:
     """
     Express interface definition file path as an (absolute prefix, relative path) tuple.
 
@@ -61,18 +62,20 @@ def interface_path_as_tuple(path):
     """
     path_as_string = str(path)
     if ':' not in path_as_string:
-        prefix = pathlib.Path.cwd()
+        prefix_path = pathlib.Path.cwd()
     else:
         prefix, _, path = path_as_string.rpartition(':')
-        prefix = pathlib.Path(os.path.abspath(prefix))
-    path = pathlib.Path(path)
-    if path.is_absolute():
+        prefix_path = pathlib.Path(os.path.abspath(prefix))
+    path_as_path = pathlib.Path(path)
+    if path_as_path.is_absolute():
         raise ValueError('Interface definition file path '
-                         f"'{path}' cannot be absolute")
-    return prefix, path
+                         f"'{path_as_path}' cannot be absolute")
+    return prefix_path, path_as_path
 
 
-def idl_tuples_from_interface_files(interface_files):
+def idl_tuples_from_interface_files(
+    interface_files: List[str]
+) -> List[str]:
     """
     Express ROS interface definition file paths as IDL tuples.
 
@@ -80,9 +83,9 @@ def idl_tuples_from_interface_files(interface_files):
     which to resolve it followed by a colon ':'. This function then applies
     the same logic as `interface_path_as_tuple`.
     """
-    idl_tuples = []
-    for path in interface_files:
-        prefix, path = interface_path_as_tuple(path)
+    idl_tuples: List[str] = []
+    for interface_path in interface_files:
+        prefix, path = interface_path_as_tuple(interface_path)
         idl_tuples.append(f'{prefix}:{path.as_posix()}')
     return idl_tuples
 
@@ -90,12 +93,12 @@ def idl_tuples_from_interface_files(interface_files):
 @contextlib.contextmanager
 def legacy_generator_arguments_file(
     *,
-    package_name,
-    interface_files,
-    include_paths,
-    templates_path,
-    output_path
-):
+    package_name: str,
+    interface_files: List[str],
+    include_paths: List[str],
+    templates_path: str,
+    output_path: str
+) -> Generator[str, None, None]:
     """
     Generate a temporary rosidl generator arguments file.
 
@@ -138,10 +141,10 @@ def legacy_generator_arguments_file(
 
 def generate_visibility_control_file(
     *,
-    package_name,
-    template_path,
-    output_path
-):
+    package_name: str,
+    template_path: str,
+    output_path: str
+) -> None:
     """
     Generate a visibility control file from a template.
 
diff --git a/rosidl_cli/rosidl_cli/command/translate/__init__.py b/rosidl_cli/rosidl_cli/command/translate/__init__.py
index 03798db3e..f5b6368f0 100644
--- a/rosidl_cli/rosidl_cli/command/translate/__init__.py
+++ b/rosidl_cli/rosidl_cli/command/translate/__init__.py
@@ -12,8 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
 import pathlib
 
+
 from rosidl_cli.command import Command
 
 from .api import translate
@@ -24,7 +26,7 @@ class TranslateCommand(Command):
 
     name = 'translate'
 
-    def add_arguments(self, parser):
+    def add_arguments(self, parser: argparse.ArgumentParser) -> None:
         parser.add_argument(
             '-o', '--output-path', metavar='PATH',
             type=pathlib.Path, default=None,
@@ -64,7 +66,7 @@ def add_arguments(self, parser):
                   'path resolution is performed against such path.')
         )
 
-    def main(self, *, args):
+    def main(self, *, args: argparse.Namespace) -> None:
         translate(
             package_name=args.package_name,
             interface_files=args.interface_files,
diff --git a/rosidl_cli/rosidl_cli/command/translate/api.py b/rosidl_cli/rosidl_cli/command/translate/api.py
index b63db278e..a7d18bd45 100644
--- a/rosidl_cli/rosidl_cli/command/translate/api.py
+++ b/rosidl_cli/rosidl_cli/command/translate/api.py
@@ -15,20 +15,21 @@
 import collections
 import os
 import pathlib
+from typing import DefaultDict, Dict, List, Optional, Union
 
 from .extensions import load_translate_extensions
 
 
 def translate(
     *,
-    package_name,
-    interface_files,
-    output_format,
-    input_format=None,
-    include_paths=None,
-    output_path=None,
-    translators=None
-):
+    package_name: str,
+    interface_files: List[str],
+    output_format: str,
+    input_format: Optional[str] = None,
+    include_paths: Optional[List[str]] = None,
+    output_path: Optional[pathlib.Path] = None,
+    translators: Optional[List[str]] = None
+) -> List[str]:
     """
     Translate interface definition files from one format to another.
 
@@ -64,7 +65,8 @@ def translate(
         raise RuntimeError('No translate extensions found')
 
     if not input_format:
-        interface_files_per_format = collections.defaultdict(list)
+        interface_files_per_format: Union[DefaultDict[str, List[str]],
+                                          Dict[str, List[str]]] = collections.defaultdict(list)
         for interface_file in interface_files:
             input_format = os.path.splitext(interface_file)[-1][1:]
             interface_files_per_format[input_format].append(interface_file)
diff --git a/rosidl_cli/rosidl_cli/command/translate/extensions.py b/rosidl_cli/rosidl_cli/command/translate/extensions.py
index f193a4804..10c3ba194 100644
--- a/rosidl_cli/rosidl_cli/command/translate/extensions.py
+++ b/rosidl_cli/rosidl_cli/command/translate/extensions.py
@@ -11,6 +11,8 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from pathlib import Path
+from typing import cast, ClassVar, List, Optional
 
 from rosidl_cli.extensions import Extension
 from rosidl_cli.extensions import load_extensions
@@ -28,13 +30,16 @@ class TranslateCommandExtension(Extension):
     * `translate`
     """
 
+    input_format: ClassVar[str]
+    output_format: ClassVar[str]
+
     def translate(
         self,
-        package_name,
-        interface_files,
-        include_paths,
-        output_path
-    ):
+        package_name: str,
+        interface_files: List[str],
+        include_paths: List[str],
+        output_path: Path
+    ) -> List[str]:
         """
         Translate interface definition files.
 
@@ -57,8 +62,10 @@ def translate(
         raise NotImplementedError()
 
 
-def load_translate_extensions(**kwargs):
+def load_translate_extensions(*, specs: Optional[List[str]], strict: bool
+                              ) -> List[TranslateCommandExtension]:
     """Load extensions for interface definition translation."""
-    return load_extensions(
-        'rosidl_cli.command.translate.extensions', **kwargs
+    extensions = load_extensions(
+        'rosidl_cli.command.translate.extensions', specs=specs, strict=strict
     )
+    return cast(List[TranslateCommandExtension], extensions)
diff --git a/rosidl_cli/rosidl_cli/common.py b/rosidl_cli/rosidl_cli/common.py
index 1f94c2c63..c0e8c9d42 100644
--- a/rosidl_cli/rosidl_cli/common.py
+++ b/rosidl_cli/rosidl_cli/common.py
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 
-def get_first_line_doc(any_type):
+def get_first_line_doc(any_type: object) -> str:
     if any_type.__doc__:
         for line in any_type.__doc__.splitlines():
             line = line.strip()
diff --git a/rosidl_cli/rosidl_cli/entry_points.py b/rosidl_cli/rosidl_cli/entry_points.py
index edab63729..6a79673f9 100644
--- a/rosidl_cli/rosidl_cli/entry_points.py
+++ b/rosidl_cli/rosidl_cli/entry_points.py
@@ -12,38 +12,41 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import importlib.metadata as importlib_metadata
 import logging
-
-try:
-    import importlib.metadata as importlib_metadata
-except ModuleNotFoundError:
-    import importlib_metadata
+import sys
+from typing import Any, Dict, List, Optional, Tuple, Union
 
 
 logger = logging.getLogger(__name__)
 
 
-def get_entry_points(group_name, *, specs=None, strict=False):
+def get_entry_points(group_name: str, *, specs: Optional[List[str]] = None, strict: bool = False
+                     ) -> Dict[str, importlib_metadata.EntryPoint]:
     """
     Get entry points from a specific group.
 
-    :param str group_name: the name of the entry point group
-    :param list specs: an optional collection of entry point names to retrieve
-    :param bool strict: whether to raise or warn on error
+    :param group_name: the name of the entry point group
+    :param specs: an optional collection of entry point names to retrieve
+    :param strict: whether to raise or warn on error
     :returns: mapping from entry point names to ``EntryPoint`` instances
-    :rtype: dict
     """
     if specs is not None:
-        specs = set(specs)
+        specs_set = set(specs)
+    else:
+        specs_set = None
     entry_points_impl = importlib_metadata.entry_points()
-    if hasattr(entry_points_impl, 'select'):
+    # Select does not exist until python 3.10
+    if sys.version_info >= (3, 10):
         groups = entry_points_impl.select(group=group_name)
     else:
-        groups = entry_points_impl.get(group_name, [])
-    entry_points = {}
+        groups: Union[Tuple[importlib_metadata.EntryPoint, ...],
+                      List[importlib_metadata.EntryPoint]] = entry_points_impl.get(group_name, [])
+
+    entry_points: Dict[str, importlib_metadata.EntryPoint] = {}
     for entry_point in groups:
         name = entry_point.name
-        if specs and name not in specs:
+        if specs_set and name not in specs_set:
             continue
         if name in entry_points:
             msg = (f"Found duplicate entry point '{name}': "
@@ -53,8 +56,8 @@ def get_entry_points(group_name, *, specs=None, strict=False):
             logger.warning(msg)
             continue
         entry_points[name] = entry_point
-    if specs:
-        pending = specs - set(entry_points)
+    if specs_set:
+        pending = specs_set - set(entry_points)
         if pending:
             msg = 'Some specs could not be met: '
             msg += ', '.join(map(str, pending))
@@ -64,21 +67,22 @@ def get_entry_points(group_name, *, specs=None, strict=False):
     return entry_points
 
 
-def load_entry_points(group_name, *, strict=False, **kwargs):
+def load_entry_points(group_name: str, *, specs: Optional[List[str]],
+                      strict: bool = False,
+                      ) -> Dict[str, Any]:
     """
     Load entry points for a specific group.
 
     See :py:meth:`get_entry_points` for further reference on
     additional keyword arguments.
 
-    :param str group_name: the name of the entry point group
-    :param bool strict: whether to raise or warn on error
+    :param group_name: the name of the entry point group
+    :param strict: whether to raise or warn on error
     :returns: mapping from entry point name to loaded entry point
-    :rtype: dict
     """
-    loaded_entry_points = {}
+    loaded_entry_points: Dict[str, Any] = {}
     for name, entry_point in get_entry_points(
-        group_name, strict=strict, **kwargs
+        group_name, strict=strict, specs=specs
     ).items():
         try:
             loaded_entry_points[name] = entry_point.load()
diff --git a/rosidl_cli/rosidl_cli/extensions.py b/rosidl_cli/rosidl_cli/extensions.py
index 7cc31afa2..bbc28c9e7 100644
--- a/rosidl_cli/rosidl_cli/extensions.py
+++ b/rosidl_cli/rosidl_cli/extensions.py
@@ -14,10 +14,19 @@
 
 import logging
 import re
+from typing import Any, Dict, Final, List, Optional, Tuple, TYPE_CHECKING, Union
 
 from rosidl_cli.entry_points import load_entry_points
 
-import yaml
+import yaml  # type: ignore[import]
+
+if TYPE_CHECKING:
+    from typing import TypedDict
+    from typing_extensions import NotRequired
+
+    class LoadExtensionsArg(TypedDict):
+        specs: NotRequired[Optional[List[str]]]
+        strict: NotRequired[bool]
 
 
 logger = logging.getLogger(__name__)
@@ -26,18 +35,18 @@
 class Extension:
     """A generic extension point."""
 
-    def __init__(self, name):
+    def __init__(self, name: str) -> None:
         self.__name = name
 
     @property
-    def name(self):
+    def name(self) -> str:
         return self.__name
 
 
-SPECS_PATTERN = re.compile(r'^(\w+)(?:\[(.+)\])?$')
+SPECS_PATTERN: Final = re.compile(r'^(\w+)(?:\[(.+)\])?$')
 
 
-def parse_extension_specification(spec):
+def parse_extension_specification(spec: str) -> Tuple[Union[str, Any], Union[Dict[Any, Any], Any]]:
     """
     Parse extension specification.
 
@@ -64,18 +73,18 @@ def parse_extension_specification(spec):
     return name, kwargs
 
 
-def load_extensions(group_name, *, specs=None, strict=False):
+def load_extensions(group_name: str, *, specs: Optional[List[str]] = None,
+                    strict: bool = False) -> List[Extension]:
     """
     Load extensions for a specific group.
 
-    :param str group_name: the name of the extension group
-    :param list specs: an optional collection of extension specs
+    :param group_name: the name of the extension group
+    :param specs: an optional collection of extension specs
       (see :py:meth:`parse_extension_specification` for spec format)
-    :param bool strict: whether to raise or warn on error
+    :param strict: whether to raise or warn on error
     :returns: a list of :py:class:`Extension` instances
-    :rtype: list
     """
-    extensions = []
+    extensions: List[Extension] = []
 
     if specs is not None:
         kwargs = dict(map(
diff --git a/rosidl_cli/test/rosidl_cli/test_common.py b/rosidl_cli/test/rosidl_cli/test_common.py
index 166f8bf0f..ccc4a6cb7 100644
--- a/rosidl_cli/test/rosidl_cli/test_common.py
+++ b/rosidl_cli/test/rosidl_cli/test_common.py
@@ -15,20 +15,20 @@
 from rosidl_cli.common import get_first_line_doc
 
 
-def test_getting_first_line_from_no_docstring():
+def test_getting_first_line_from_no_docstring() -> None:
     func = test_getting_first_line_from_no_docstring
     line = get_first_line_doc(func)
     assert line == ''
 
 
-def test_getting_first_line_from_docstring():
+def test_getting_first_line_from_docstring() -> None:
     """Check it gets the first line."""
     func = test_getting_first_line_from_docstring
     line = get_first_line_doc(func)
     assert line == 'Check it gets the first line'
 
 
-def test_getting_first_line_from_multiline_docstring():
+def test_getting_first_line_from_multiline_docstring() -> None:
     """
     Check it really gets the first non-empty line.
 
diff --git a/rosidl_cli/test/rosidl_cli/test_extensions.py b/rosidl_cli/test/rosidl_cli/test_extensions.py
index 7e3dd2158..94af493af 100644
--- a/rosidl_cli/test/rosidl_cli/test_extensions.py
+++ b/rosidl_cli/test/rosidl_cli/test_extensions.py
@@ -17,7 +17,7 @@
 from rosidl_cli.extensions import parse_extension_specification
 
 
-def test_extension_specification_parsing():
+def test_extension_specification_parsing() -> None:
     with pytest.raises(ValueError):
         parse_extension_specification('bad[')
 
diff --git a/rosidl_cli/test/rosidl_cli/test_helpers.py b/rosidl_cli/test/rosidl_cli/test_helpers.py
index 5a16f684f..bba66d4e9 100644
--- a/rosidl_cli/test/rosidl_cli/test_helpers.py
+++ b/rosidl_cli/test/rosidl_cli/test_helpers.py
@@ -15,6 +15,7 @@
 import json
 import os
 import pathlib
+from typing import Iterable
 
 import pytest
 
@@ -22,7 +23,7 @@
 from rosidl_cli.command.helpers import legacy_generator_arguments_file
 
 
-def test_interface_path_as_tuple():
+def test_interface_path_as_tuple() -> None:
     prefix, path = interface_path_as_tuple('/tmp:msg/Empty.idl')
     assert pathlib.Path('msg/Empty.idl') == path
     assert pathlib.Path(os.path.abspath('/tmp')) == prefix
@@ -37,7 +38,7 @@ def test_interface_path_as_tuple():
 
 
 @pytest.fixture
-def current_path(request):
+def current_path(request: pytest.FixtureRequest) -> Iterable[pathlib.Path]:
     path = pathlib.Path(request.module.__file__)
     path = path.resolve()
     path = path.parent
@@ -49,7 +50,7 @@ def current_path(request):
         os.chdir(str(cwd))
 
 
-def test_legacy_generator_arguments_file(current_path):
+def test_legacy_generator_arguments_file(current_path: pathlib.Path) -> None:
     with legacy_generator_arguments_file(
         package_name='foo',
         interface_files=['msg/Foo.idl'],
diff --git a/rosidl_cli/test/test_copyright.py b/rosidl_cli/test/test_copyright.py
index cf0fae31f..66a7d63eb 100644
--- a/rosidl_cli/test/test_copyright.py
+++ b/rosidl_cli/test/test_copyright.py
@@ -18,6 +18,6 @@
 
 @pytest.mark.copyright
 @pytest.mark.linter
-def test_copyright():
+def test_copyright() -> None:
     rc = main(argv=['.', 'test'])
     assert rc == 0, 'Found errors'
diff --git a/rosidl_cli/test/test_flake8.py b/rosidl_cli/test/test_flake8.py
index 27ee1078f..eac16eef9 100644
--- a/rosidl_cli/test/test_flake8.py
+++ b/rosidl_cli/test/test_flake8.py
@@ -18,7 +18,7 @@
 
 @pytest.mark.flake8
 @pytest.mark.linter
-def test_flake8():
+def test_flake8() -> None:
     rc, errors = main_with_errors(argv=[])
     assert rc == 0, \
         'Found %d code style errors / warnings:\n' % len(errors) + \
diff --git a/rosidl_cli/test/test_mypy.py b/rosidl_cli/test/test_mypy.py
new file mode 100644
index 000000000..97e4f502a
--- /dev/null
+++ b/rosidl_cli/test/test_mypy.py
@@ -0,0 +1,23 @@
+# Copyright 2024 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ament_mypy.main import main
+import pytest
+
+
+@pytest.mark.mypy
+@pytest.mark.linter
+def test_mypy() -> None:
+    rc = main(argv=[])
+    assert rc == 0, 'Found type errors!'
diff --git a/rosidl_cli/test/test_pep257.py b/rosidl_cli/test/test_pep257.py
index 0e38a6c60..4ae521a5a 100644
--- a/rosidl_cli/test/test_pep257.py
+++ b/rosidl_cli/test/test_pep257.py
@@ -18,6 +18,6 @@
 
 @pytest.mark.linter
 @pytest.mark.pep257
-def test_pep257():
+def test_pep257() -> None:
     rc = main(argv=[])
     assert rc == 0, 'Found code style errors / warnings'
diff --git a/rosidl_cli/test/test_xmllint.py b/rosidl_cli/test/test_xmllint.py
index f46285e71..08bf7fd78 100644
--- a/rosidl_cli/test/test_xmllint.py
+++ b/rosidl_cli/test/test_xmllint.py
@@ -18,6 +18,6 @@
 
 @pytest.mark.linter
 @pytest.mark.xmllint
-def test_xmllint():
+def test_xmllint() -> None:
     rc = main(argv=[])
     assert rc == 0, 'Found errors'