diff --git a/mypy.ini b/mypy.ini
index 313e479..3a36ba2 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,4 +1,35 @@
 [mypy]
+check_untyped_defs = True
+disallow_any_generics = True
+disallow_incomplete_defs = True
+disallow_subclassing_any = True
+disallow_untyped_calls = True
+disallow_untyped_decorators = True
+disallow_untyped_defs = True
+no_implicit_optional = True
+no_implicit_reexport = True
+pretty = True
+show_column_numbers = True
+show_error_codes = True
+show_error_context = True
+strict_equality = True
+warn_redundant_casts = True
+warn_return_any = True
+warn_unreachable = True
+warn_unused_configs = True
+warn_unused_ignores = True
 
-[mypy-tomlkit.*,pytest,pytest_mock,_pytest.*]
+[mypy-_pytest.*]
+ignore_missing_imports = True
+
+[mypy-pytest]
+ignore_missing_imports = True
+
+[mypy-pytest_mock]
+ignore_missing_imports = True
+
+[mypy-tests.*]
+disallow_untyped_decorators = False
+
+[mypy-tomlkit.*]
 ignore_missing_imports = True
diff --git a/src/toml_validator/py.typed b/src/toml_validator/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_main.py b/tests/test_main.py
index 420fc16..d152eb9 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -1,27 +1,28 @@
 """Test cases for the __main__ module."""
+from typing import Any
 from unittest.mock import Mock
 
+import click.testing
 import pytest
-from click.testing import CliRunner
 from pytest_mock import MockFixture
 
 from toml_validator import __main__
 
 
 @pytest.fixture
-def runner() -> CliRunner:
+def runner() -> click.testing.CliRunner:
     """Fixture for invoking command-line interfaces."""
-    return CliRunner()
+    return click.testing.CliRunner()
 
 
 @pytest.fixture
-def mock_validation_validate_extension(mocker: MockFixture) -> Mock:
+def mock_validation_validate_extension(mocker: MockFixture) -> Any:
     """Fixture for mocking validation.validate_extension."""
     return mocker.patch("toml_validator.validation.validate_extension")
 
 
 @pytest.fixture
-def mock_validation_validate_toml_no_error(mocker: MockFixture) -> Mock:
+def mock_validation_validate_toml_no_error(mocker: MockFixture) -> Any:
     """Fixture for mocking validation.validate_toml with no errors."""
     mock = mocker.patch("toml_validator.validation.validate_toml")
     mock.return_value = ""
@@ -29,24 +30,24 @@ def mock_validation_validate_toml_no_error(mocker: MockFixture) -> Mock:
 
 
 @pytest.fixture
-def mock_validation_validate_toml_with_error(mocker: MockFixture) -> Mock:
+def mock_validation_validate_toml_with_error(mocker: MockFixture) -> Any:
     """Fixture for mocking validation.validate_toml with error."""
     mock = mocker.patch("toml_validator.validation.validate_toml")
     mock.return_value = "|some error description|"
     return mock
 
 
-def test_main_without_argument(runner: CliRunner):
+def test_main_without_argument(runner: click.testing.CliRunner) -> None:
     """It exits with a status code of 2."""
     result = runner.invoke(__main__.main)
     assert result.exit_code == 2
 
 
 def test_main_with_argument_success(
-    runner: CliRunner,
+    runner: click.testing.CliRunner,
     mock_validation_validate_extension: Mock,
     mock_validation_validate_toml_no_error: Mock,
-):
+) -> None:
     """It exits with a status code of zero."""
     with runner.isolated_filesystem():
         with open("file.toml", "w") as f:
@@ -60,10 +61,10 @@ def test_main_with_argument_success(
 
 
 def test_main_with_argument_fail(
-    runner: CliRunner,
+    runner: click.testing.CliRunner,
     mock_validation_validate_extension: Mock,
     mock_validation_validate_toml_with_error: Mock,
-):
+) -> None:
     """It outputs error."""
     with runner.isolated_filesystem():
         with open("file.toml", "w") as f:
@@ -77,7 +78,9 @@ def test_main_with_argument_fail(
 
 
 @pytest.mark.e2e
-def test_main_without_arguments_in_production_env(runner: CliRunner):
+def test_main_without_arguments_in_production_env(
+    runner: click.testing.CliRunner,
+) -> None:
     """It exits with a status code of 2 (e2e)."""
     result = runner.invoke(__main__.main)
     assert result.exit_code == 2
diff --git a/tests/test_validation.py b/tests/test_validation.py
index 9526f8b..8420319 100644
--- a/tests/test_validation.py
+++ b/tests/test_validation.py
@@ -1,4 +1,5 @@
 """Test cases for the validation module."""
+from typing import Any
 from unittest.mock import Mock
 
 import pytest
@@ -9,13 +10,13 @@
 
 
 @pytest.fixture
-def mock_tomlkit_parse(mocker: MockFixture) -> Mock:
+def mock_tomlkit_parse(mocker: MockFixture) -> Any:
     """Fixture for mocking tomlkit.parse."""
     return mocker.patch("tomlkit.parse")
 
 
 @pytest.fixture
-def mock_tomlkit_parse_exception(mocker: MockFixture) -> Mock:
+def mock_tomlkit_parse_exception(mocker: MockFixture) -> Any:
     """Fixture for mocking tomlkit.parse."""
     mock = mocker.patch("tomlkit.parse")
     mock.side_effect = TOMLKitError("|some tomlkit error|")
@@ -23,13 +24,13 @@ def mock_tomlkit_parse_exception(mocker: MockFixture) -> Mock:
 
 
 @pytest.fixture
-def mock_open_valid_file(mocker: MockFixture) -> Mock:
+def mock_open_valid_file(mocker: MockFixture) -> Any:
     """Fixture for mocking build-in open for valid TOML file."""
     return mocker.patch("builtins.open", mocker.mock_open(read_data="[x]\na = 3"))
 
 
 @pytest.fixture
-def mock_open_invalid_file(mocker: MockFixture) -> Mock:
+def mock_open_invalid_file(mocker: MockFixture) -> Any:
     """Fixture for mocking build-in open for valid TOML file."""
     return mocker.patch(
         "builtins.open", mocker.mock_open(read_data="[x]\na = 3\n[x]\na = 3")
@@ -62,12 +63,12 @@ def test_validate_toml_with_error(
 
 
 @pytest.mark.e2e
-def test_validate_toml_no_error_production(mock_open_valid_file) -> None:
+def test_validate_toml_no_error_production(mock_open_valid_file: Mock) -> None:
     """It returns no errors when valid TOML (e2e)."""
     assert validation.validate_toml("file.toml") == ""
 
 
 @pytest.mark.e2e
-def test_validate_toml_with_error_production(mock_open_invalid_file) -> None:
+def test_validate_toml_with_error_production(mock_open_invalid_file: Mock) -> None:
     """It returns errors when invalid TOML (e2e)."""
     assert validation.validate_toml("file.toml") == 'Key "x" already exists.'