diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0d1da4e..eb42137 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,11 +27,13 @@ jobs:
     - name: Install checkers
       run: |
         python -mpip install --upgrade pip
-        python -mpip install black flake8
+        python -mpip install black flake8 mypy types-PyYaml
     - name: flake
       run: flake8 .
     - name: black
       run: black --check --diff --color --quiet .
+    - name: mypy
+      run: mypy
 
   # REPLACE BY: job which python -mbuild, and uploads the sdist and wheel to artifacts
   # build is not binary so can just build the one using whatever python version
diff --git a/pyproject.toml b/pyproject.toml
index b42d432..2be9ead 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,3 +42,54 @@ classifiers = [
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Implementation :: PyPy"
 ]
+
+[tool.mypy]
+python_version = "3.8"
+files = "src,tests"
+
+# can't use strict because it's only global
+
+# these two are global
+warn_unused_configs = true
+warn_redundant_casts = true
+
+# these can be overridden (maybe?)
+strict_equality = true
+strict_concatenate = true
+check_untyped_defs = true
+disallow_subclassing_any = true
+disallow_untyped_decorators = true
+disallow_any_generics = true
+disallow_untyped_calls = true
+disallow_incomplete_defs = true
+disallow_untyped_defs = true
+no_implicit_reexport = true
+warn_return_any = true
+
+[[tool.mypy.overrides]]
+module = "ua_parser.user_agent_parser"
+
+#check_untyped_defs = false
+disallow_untyped_calls = false
+#disallow_incomplete_defs = false
+disallow_untyped_defs = false
+
+[[tool.mypy.overrides]]
+module = [
+       "test_core",
+       "test_caches",
+       "test_parsers_basics",
+]
+
+#check_untyped_defs = false
+#disallow_untyped_calls = false
+#disallow_incomplete_defs = false
+disallow_untyped_defs = false
+
+[[tool.mypy.overrides]]
+module = "test_legacy"
+
+#check_untyped_defs = false
+disallow_untyped_calls = false
+#disallow_incomplete_defs = false
+disallow_untyped_defs = false
diff --git a/src/ua_parser/user_agent_parser.py b/src/ua_parser/user_agent_parser.py
index d44133a..7a5ba12 100644
--- a/src/ua_parser/user_agent_parser.py
+++ b/src/ua_parser/user_agent_parser.py
@@ -181,7 +181,7 @@ def Parse(self, user_agent_string: str) -> Tuple[
 _PARSE_CACHE: Dict[str, Dict[str, Any]] = {}
 
 
-def _lookup(ua: str):
+def _lookup(ua):
     if not isinstance(ua, str):
         raise TypeError(f"Expected user agent to be a string, got {ua!r}")
 
@@ -204,7 +204,7 @@ def _cached(ua, key, fn):
     return r
 
 
-def Parse(user_agent_string: str, **_jsParseBits):
+def Parse(user_agent_string, **_jsParseBits):
     """Parse all the things
     Args:
       user_agent_string: the full user agent string
diff --git a/tox.ini b/tox.ini
index 57b17f9..6dac8a2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,12 +2,12 @@
 min_version = 4.0
 env_list = py3{8,9,10,11,12}
            pypy3.{8,9,10}
-           flake8, black
+           flake8, black, typecheck
 labels =
     test = py3{8,9,10,11,12},pypy3.{8,9,10}
     cpy = py3{8,9,10,11,12}
     pypy = pypy3.{8,9,10}
-    check = flake8, black
+    check = flake8, black, typecheck
 
 [testenv]
 # wheel install
@@ -30,7 +30,14 @@ commands = flake8 {posargs}
 [testenv:black]
 package = skip
 deps = black
-commands = black --check --diff .
+commands = black --check --diff {posargs:.}
+
+[testenv:typecheck]
+package = skip
+deps =
+     mypy
+     types-PyYaml
+commands = mypy {posargs:}
 
 [flake8]
 max_line_length = 88