diff --git a/.github/workflows/pr_typecheck.yml b/.github/workflows/pr_typecheck.yml
new file mode 100644
index 0000000000..6e093b4996
--- /dev/null
+++ b/.github/workflows/pr_typecheck.yml
@@ -0,0 +1,43 @@
+name: PR Typecheck
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+    paths:
+      - "aeon/**"
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  typecheck:
+    # run the code coverage job if a PR has the '' label
+    if: ${{ github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'run typecheck test') }}
+    runs-on: ubuntu-22.04
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Python 3.10
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+
+      - name: Install aeon, dependencies and mypy
+        uses: nick-fields/retry@v3
+        with:
+          timeout_minutes: 30
+          max_attempts: 3
+          command: python -m pip install .[all_extras,unstable_extras,dev] mypy
+
+      - name: Show dependencies
+        run: python -m pip list
+
+      - name: Run mypy typecheck
+        run: mypy aeon/
diff --git a/aeon/classification/distance_based/_proximity_forest.py b/aeon/classification/distance_based/_proximity_forest.py
index aa034f54fc..44871a2500 100644
--- a/aeon/classification/distance_based/_proximity_forest.py
+++ b/aeon/classification/distance_based/_proximity_forest.py
@@ -3,6 +3,8 @@
 The Proximity Forest is an ensemble of Proximity Trees.
 """
 
+from typing import Optional
+
 __all__ = ["ProximityForest"]
 
 from typing import Union
@@ -87,7 +89,7 @@ def __init__(
         self,
         n_trees=100,
         n_splitters: int = 5,
-        max_depth: int = None,
+        max_depth: Optional[int] = None,
         min_samples_split: int = 2,
         random_state: Union[int, np.random.RandomState, None] = None,
         n_jobs: int = 1,
diff --git a/aeon/classification/distance_based/_proximity_tree.py b/aeon/classification/distance_based/_proximity_tree.py
index dda47493f2..f2c3cd36e6 100644
--- a/aeon/classification/distance_based/_proximity_tree.py
+++ b/aeon/classification/distance_based/_proximity_tree.py
@@ -5,7 +5,7 @@
 aeon distances.
 """
 
-from typing import Union
+from typing import Optional, Union
 
 import numpy as np
 from numba import njit
@@ -118,7 +118,7 @@ class ProximityTree(BaseClassifier):
     def __init__(
         self,
         n_splitters: int = 5,
-        max_depth: int = None,
+        max_depth: Optional[int] = None,
         min_samples_split: int = 2,
         random_state: Union[int, np.random.RandomState, None] = None,
     ) -> None:
diff --git a/aeon/classification/distance_based/_time_series_neighbors.py b/aeon/classification/distance_based/_time_series_neighbors.py
index b2702ad307..20ca5a3f8d 100644
--- a/aeon/classification/distance_based/_time_series_neighbors.py
+++ b/aeon/classification/distance_based/_time_series_neighbors.py
@@ -5,6 +5,8 @@
 distances in aeon.distances.
 """
 
+from typing import Optional
+
 __maintainer__ = []
 __all__ = ["KNeighborsTimeSeriesClassifier"]
 
@@ -72,7 +74,7 @@ class KNeighborsTimeSeriesClassifier(BaseClassifier):
     def __init__(
         self,
         distance: Union[str, Callable] = "dtw",
-        distance_params: dict = None,
+        distance_params: Optional[dict] = None,
         n_neighbors: int = 1,
         weights: Union[str, Callable] = "uniform",
         n_jobs: int = 1,
diff --git a/aeon/classification/shapelet_based/_sast.py b/aeon/classification/shapelet_based/_sast.py
index 26b5144660..096a845529 100644
--- a/aeon/classification/shapelet_based/_sast.py
+++ b/aeon/classification/shapelet_based/_sast.py
@@ -3,6 +3,8 @@
 Pipeline classifier using the SAST transformer and an sklearn classifier.
 """
 
+from typing import Optional
+
 __maintainer__ = ["TonyBagnall"]
 __all__ = ["SASTClassifier"]
 
@@ -69,7 +71,7 @@ def __init__(
         length_list=None,
         stride: int = 1,
         nb_inst_per_class: int = 1,
-        seed: int = None,
+        seed: Optional[int] = None,
         classifier=None,
         n_jobs: int = -1,
     ) -> None:
diff --git a/aeon/clustering/_clara.py b/aeon/clustering/_clara.py
index d6cdc8957b..0121922fbb 100644
--- a/aeon/clustering/_clara.py
+++ b/aeon/clustering/_clara.py
@@ -1,5 +1,7 @@
 """Time series kmedoids."""
 
+from typing import Optional
+
 __maintainer__ = []
 
 from typing import Callable, Union
@@ -118,14 +120,14 @@ def __init__(
         n_clusters: int = 8,
         init_algorithm: Union[str, np.ndarray] = "random",
         distance: Union[str, Callable] = "msm",
-        n_samples: int = None,
+        n_samples: Optional[int] = None,
         n_sampling_iters: int = 10,
         n_init: int = 1,
         max_iter: int = 300,
         tol: float = 1e-6,
         verbose: bool = False,
-        random_state: Union[int, RandomState] = None,
-        distance_params: dict = None,
+        random_state: Optional[Union[int, RandomState]] = None,
+        distance_params: Optional[dict] = None,
     ):
         self.init_algorithm = init_algorithm
         self.distance = distance
diff --git a/aeon/clustering/_clarans.py b/aeon/clustering/_clarans.py
index c1790e49ec..0d15bc7b81 100644
--- a/aeon/clustering/_clarans.py
+++ b/aeon/clustering/_clarans.py
@@ -1,5 +1,7 @@
 """Time series kmedoids."""
 
+from typing import Optional
+
 __maintainer__ = []
 
 import math
@@ -104,11 +106,11 @@ def __init__(
         n_clusters: int = 8,
         init_algorithm: Union[str, np.ndarray] = "random",
         distance: Union[str, Callable] = "msm",
-        max_neighbours: int = None,
+        max_neighbours: Optional[int] = None,
         n_init: int = 10,
         verbose: bool = False,
-        random_state: Union[int, RandomState] = None,
-        distance_params: dict = None,
+        random_state: Optional[Union[int, RandomState]] = None,
+        distance_params: Optional[dict] = None,
     ):
         self.max_neighbours = max_neighbours
 
diff --git a/aeon/clustering/_k_means.py b/aeon/clustering/_k_means.py
index eecd62172a..54d05e8c84 100644
--- a/aeon/clustering/_k_means.py
+++ b/aeon/clustering/_k_means.py
@@ -1,5 +1,7 @@
 """Time series kmeans."""
 
+from typing import Optional
+
 __maintainer__ = []
 
 from typing import Callable, Union
@@ -163,11 +165,11 @@ def __init__(
         max_iter: int = 300,
         tol: float = 1e-6,
         verbose: bool = False,
-        random_state: Union[int, RandomState] = None,
+        random_state: Optional[Union[int, RandomState]] = None,
         averaging_method: Union[str, Callable[[np.ndarray], np.ndarray]] = "ba",
-        distance_params: dict = None,
-        average_params: dict = None,
-        init_algorithm: Union[str, np.ndarray] = None,
+        distance_params: Optional[dict] = None,
+        average_params: Optional[dict] = None,
+        init_algorithm: Optional[Union[str, np.ndarray]] = None,
     ):
         self.init = init
         self.init_algorithm = init_algorithm
diff --git a/aeon/clustering/_k_medoids.py b/aeon/clustering/_k_medoids.py
index 021f20d726..9a0a91ae9c 100644
--- a/aeon/clustering/_k_medoids.py
+++ b/aeon/clustering/_k_medoids.py
@@ -1,5 +1,7 @@
 """Time series kmedoids."""
 
+from typing import Optional
+
 __maintainer__ = []
 
 import warnings
@@ -157,8 +159,8 @@ def __init__(
         max_iter: int = 300,
         tol: float = 1e-6,
         verbose: bool = False,
-        random_state: Union[int, RandomState] = None,
-        distance_params: dict = None,
+        random_state: Optional[Union[int, RandomState]] = None,
+        distance_params: Optional[dict] = None,
     ):
         self.init_algorithm = init_algorithm
         self.distance = distance
diff --git a/aeon/clustering/_k_shape.py b/aeon/clustering/_k_shape.py
index 8331533a21..585e7dc841 100644
--- a/aeon/clustering/_k_shape.py
+++ b/aeon/clustering/_k_shape.py
@@ -1,6 +1,6 @@
 """Time series kshapes."""
 
-from typing import Union
+from typing import Optional, Union
 
 import numpy as np
 from numpy.random import RandomState
@@ -82,7 +82,7 @@ def __init__(
         max_iter: int = 300,
         tol: float = 1e-4,
         verbose: bool = False,
-        random_state: Union[int, RandomState] = None,
+        random_state: Optional[Union[int, RandomState]] = None,
     ):
         self.init_algorithm = init_algorithm
         self.n_init = n_init
diff --git a/aeon/clustering/_k_shapes.py b/aeon/clustering/_k_shapes.py
index 31dfcd6d27..6a3ae9eb44 100644
--- a/aeon/clustering/_k_shapes.py
+++ b/aeon/clustering/_k_shapes.py
@@ -1,6 +1,6 @@
 """Time series kshapes."""
 
-from typing import Union
+from typing import Optional, Union
 
 import numpy as np
 from deprecated.sphinx import deprecated
@@ -83,7 +83,7 @@ def __init__(
         max_iter: int = 300,
         tol: float = 1e-4,
         verbose: bool = False,
-        random_state: Union[int, RandomState] = None,
+        random_state: Optional[Union[int, RandomState]] = None,
     ):
         self.init_algorithm = init_algorithm
         self.n_init = n_init
diff --git a/aeon/clustering/_kernel_k_means.py b/aeon/clustering/_kernel_k_means.py
index 5c3fd1edcd..f39d1c5059 100644
--- a/aeon/clustering/_kernel_k_means.py
+++ b/aeon/clustering/_kernel_k_means.py
@@ -1,6 +1,6 @@
 """Time series kernel kmeans."""
 
-from typing import Union
+from typing import Optional, Union
 
 import numpy as np
 from numpy.random import RandomState
@@ -99,7 +99,7 @@ def __init__(
         kernel_params: Union[dict, None] = None,
         verbose: bool = False,
         n_jobs: Union[int, None] = None,
-        random_state: Union[int, RandomState] = None,
+        random_state: Optional[Union[int, RandomState]] = None,
     ):
         self.kernel = kernel
         self.n_init = n_init
diff --git a/aeon/clustering/base.py b/aeon/clustering/base.py
index c971a680fe..bf4b6c83e7 100644
--- a/aeon/clustering/base.py
+++ b/aeon/clustering/base.py
@@ -1,5 +1,7 @@
 """Base class for clustering."""
 
+from typing import Optional
+
 __maintainer__ = []
 __all__ = ["BaseClusterer"]
 
@@ -22,7 +24,7 @@ class BaseClusterer(BaseCollectionEstimator, ABC):
         Number of clusters for model.
     """
 
-    def __init__(self, n_clusters: int = None):
+    def __init__(self, n_clusters: Optional[int] = None):
         self.n_clusters = n_clusters
         # required for compatibility with some sklearn interfaces e.g.
         # CalibratedClassifierCV
diff --git a/aeon/datasets/_data_loaders.py b/aeon/datasets/_data_loaders.py
index 4a31d24a97..c5af7189ec 100644
--- a/aeon/datasets/_data_loaders.py
+++ b/aeon/datasets/_data_loaders.py
@@ -1,5 +1,7 @@
 """Dataset loading functions."""
 
+from typing import Optional
+
 __all__ = [  # Load functions
     "load_from_tsfile",
     "load_from_tsf_file",
@@ -680,7 +682,7 @@ def load_from_tsv_file(full_file_path_and_name):
 def _convert_tsf_to_hierarchical(
     data: pd.DataFrame,
     metadata,
-    freq: str = None,
+    freq: Optional[str] = None,
     value_column_name: str = "series_value",
 ) -> pd.DataFrame:
     """Convert the data from default_tsf to pd_multiindex_hier.
diff --git a/aeon/regression/distance_based/_time_series_neighbors.py b/aeon/regression/distance_based/_time_series_neighbors.py
index a0d7275d23..2de7285a23 100644
--- a/aeon/regression/distance_based/_time_series_neighbors.py
+++ b/aeon/regression/distance_based/_time_series_neighbors.py
@@ -5,6 +5,8 @@
 It can also be used with callables, or aeon (pairwise transformer) estimators.
 """
 
+from typing import Optional
+
 __maintainer__ = []
 __all__ = ["KNeighborsTimeSeriesRegressor"]
 
@@ -72,7 +74,7 @@ class KNeighborsTimeSeriesRegressor(BaseRegressor):
     def __init__(
         self,
         distance: Union[str, Callable] = "dtw",
-        distance_params: dict = None,
+        distance_params: Optional[dict] = None,
         n_neighbors: int = 1,
         weights: Union[str, Callable] = "uniform",
         n_jobs: int = 1,
diff --git a/aeon/segmentation/_ggs.py b/aeon/segmentation/_ggs.py
index 7fab9217b9..c423dd2836 100644
--- a/aeon/segmentation/_ggs.py
+++ b/aeon/segmentation/_ggs.py
@@ -36,6 +36,7 @@
 import logging
 import math
 from dataclasses import dataclass, field
+from typing import Optional
 
 import numpy as np
 import numpy.typing as npt
@@ -457,7 +458,7 @@ def __init__(
         lamb: float = 1.0,
         max_shuffles: int = 250,
         verbose: bool = False,
-        random_state: int = None,
+        random_state: Optional[int] = None,
     ):
         self.k_max = k_max
         self.lamb = lamb
diff --git a/aeon/segmentation/_hmm.py b/aeon/segmentation/_hmm.py
index b23f5a761c..49c8b277b5 100644
--- a/aeon/segmentation/_hmm.py
+++ b/aeon/segmentation/_hmm.py
@@ -7,6 +7,7 @@
 """
 
 import warnings
+from typing import Optional
 
 import numpy as np
 from scipy.stats import norm
@@ -137,7 +138,7 @@ def __init__(
         self,
         emission_funcs: list,
         transition_prob_mat: np.ndarray,
-        initial_probs: np.ndarray = None,
+        initial_probs: Optional[np.ndarray] = None,
     ):
         self.initial_probs = initial_probs
         self.emission_funcs = emission_funcs
diff --git a/aeon/similarity_search/matrix_profiles/stomp.py b/aeon/similarity_search/matrix_profiles/stomp.py
index 5bfdfa0959..e95b981f46 100644
--- a/aeon/similarity_search/matrix_profiles/stomp.py
+++ b/aeon/similarity_search/matrix_profiles/stomp.py
@@ -1,5 +1,7 @@
 """Implementation of stomp for euclidean and squared euclidean distance profile."""
 
+from typing import Optional
+
 __maintainer__ = ["baraline"]
 
 
@@ -29,7 +31,7 @@ def stomp_euclidean_matrix_profile(
     k: int = 1,
     threshold: float = np.inf,
     inverse_distance: bool = False,
-    exclusion_size: int = None,
+    exclusion_size: Optional[int] = None,
 ):
     """
     Compute a euclidean euclidean matrix profile using STOMP [1]_.
@@ -109,7 +111,7 @@ def stomp_squared_matrix_profile(
     k: int = 1,
     threshold: float = np.inf,
     inverse_distance: bool = False,
-    exclusion_size: int = None,
+    exclusion_size: Optional[int] = None,
 ):
     """
     Compute a squared euclidean matrix profile using STOMP [1]_.
@@ -198,7 +200,7 @@ def stomp_normalized_euclidean_matrix_profile(
     k: int = 1,
     threshold: float = np.inf,
     inverse_distance: bool = False,
-    exclusion_size: int = None,
+    exclusion_size: Optional[int] = None,
 ):
     """
     Compute a euclidean matrix profile using STOMP [1]_.
@@ -296,7 +298,7 @@ def stomp_normalized_squared_matrix_profile(
     k: int = 1,
     threshold: float = np.inf,
     inverse_distance: bool = False,
-    exclusion_size: int = None,
+    exclusion_size: Optional[int] = None,
 ):
     """
     Compute a squared euclidean matrix profile using STOMP [1]_.
diff --git a/aeon/testing/data_generation/hierarchical.py b/aeon/testing/data_generation/hierarchical.py
index 1c28a5366c..178ee25f7b 100644
--- a/aeon/testing/data_generation/hierarchical.py
+++ b/aeon/testing/data_generation/hierarchical.py
@@ -1,5 +1,7 @@
 """Hierarchical Data Generators."""
 
+from typing import Optional
+
 __maintainer__ = []
 
 from itertools import product
@@ -20,8 +22,8 @@ def _make_hierarchical(
     same_cutoff: bool = True,
     n_columns: int = 1,
     all_positive: bool = True,
-    index_type: str = None,
-    random_state: Union[int, np.random.RandomState] = None,
+    index_type: Optional[str] = None,
+    random_state: Optional[Union[int, np.random.RandomState]] = None,
     add_nan: bool = False,
 ) -> pd.DataFrame:
     """Generate hierarchical multiindex type for testing.
diff --git a/aeon/testing/data_generation/segmentation.py b/aeon/testing/data_generation/segmentation.py
index 41c3ab9fe9..b8ccd22aff 100644
--- a/aeon/testing/data_generation/segmentation.py
+++ b/aeon/testing/data_generation/segmentation.py
@@ -1,6 +1,6 @@
 """Synthetic data generating functions."""
 
-from typing import Union
+from typing import Optional, Union
 
 import numpy as np
 import numpy.typing as npt
@@ -11,8 +11,8 @@ def piecewise_normal_multivariate(
     means: npt.ArrayLike,
     lengths: npt.ArrayLike,
     variances: Union[npt.ArrayLike, float] = 1.0,
-    covariances: npt.ArrayLike = None,
-    random_state: Union[int, np.random.RandomState] = None,
+    covariances: Optional[npt.ArrayLike] = None,
+    random_state: Optional[Union[int, np.random.RandomState]] = None,
 ) -> npt.ArrayLike:
     """
     Generate multivariate series from segments.
@@ -136,7 +136,7 @@ def piecewise_normal(
     means: npt.ArrayLike,
     lengths: npt.ArrayLike,
     std_dev: Union[npt.ArrayLike, float] = 1.0,
-    random_state: Union[int, np.random.RandomState] = None,
+    random_state: Optional[Union[int, np.random.RandomState]] = None,
 ) -> npt.ArrayLike:
     """
     Generate series from segments.
@@ -199,7 +199,7 @@ def piecewise_multinomial(
     n_trials: int,
     lengths: npt.ArrayLike,
     p_vals: npt.ArrayLike,
-    random_state: Union[int, np.random.RandomState] = None,
+    random_state: Optional[Union[int, np.random.RandomState]] = None,
 ) -> npt.ArrayLike:
     """
     Generate series from segments.
@@ -276,7 +276,7 @@ def piecewise_multinomial(
 def piecewise_poisson(
     lambdas: npt.ArrayLike,
     lengths: npt.ArrayLike,
-    random_state: Union[int, np.random.RandomState] = None,
+    random_state: Optional[Union[int, np.random.RandomState]] = None,
 ) -> npt.ArrayLike:
     """
     Generate series using Possion distribution.
diff --git a/aeon/testing/estimator_checking/_estimator_checking.py b/aeon/testing/estimator_checking/_estimator_checking.py
index a7d71a8c2b..bd5af8ff88 100644
--- a/aeon/testing/estimator_checking/_estimator_checking.py
+++ b/aeon/testing/estimator_checking/_estimator_checking.py
@@ -1,5 +1,7 @@
 """Interface compliance checkers for aeon estimators."""
 
+from typing import Optional
+
 __maintainer__ = ["MatthewMiddlehurst"]
 __all__ = [
     "parametrize_with_checks",
@@ -97,10 +99,10 @@ def check_estimator(
     estimator: Union[BaseEstimator, type[BaseEstimator]],
     raise_exceptions: bool = False,
     use_first_parameter_set: bool = False,
-    checks_to_run: Union[str, list[str]] = None,
-    checks_to_exclude: Union[str, list[str]] = None,
-    full_checks_to_run: Union[str, list[str]] = None,
-    full_checks_to_exclude: Union[str, list[str]] = None,
+    checks_to_run: Optional[Union[str, list[str]]] = None,
+    checks_to_exclude: Optional[Union[str, list[str]]] = None,
+    full_checks_to_run: Optional[Union[str, list[str]]] = None,
+    full_checks_to_exclude: Optional[Union[str, list[str]]] = None,
     verbose: bool = False,
 ):
     """Check if estimator adheres to `aeon` conventions.
diff --git a/aeon/testing/mock_estimators/_mock_clusterers.py b/aeon/testing/mock_estimators/_mock_clusterers.py
index ff79c192e7..0563129909 100644
--- a/aeon/testing/mock_estimators/_mock_clusterers.py
+++ b/aeon/testing/mock_estimators/_mock_clusterers.py
@@ -1,3 +1,5 @@
+from typing import Optional
+
 import numpy as np
 
 from aeon.clustering.base import BaseClusterer
@@ -7,7 +9,7 @@
 class MockCluster(BaseClusterer):
     """Mock Cluster for testing base class fit/predict."""
 
-    def __init__(self, n_clusters: int = None):
+    def __init__(self, n_clusters: Optional[int] = None):
         super().__init__(n_clusters)
 
     def _fit(self, X):
diff --git a/aeon/transformations/collection/channel_selection/_channel_scorer.py b/aeon/transformations/collection/channel_selection/_channel_scorer.py
index 5a59257fec..32c211dceb 100644
--- a/aeon/transformations/collection/channel_selection/_channel_scorer.py
+++ b/aeon/transformations/collection/channel_selection/_channel_scorer.py
@@ -1,4 +1,5 @@
 import math
+from typing import Optional
 
 import numpy as np
 from sklearn.metrics import accuracy_score
@@ -40,7 +41,7 @@ class methods. Approximately as described in [1]_.
 
     def __init__(
         self,
-        classifier: BaseClassifier = None,
+        classifier: Optional[BaseClassifier] = None,
         proportion: float = 0.4,
     ):
         self.proportion = proportion
diff --git a/aeon/transformations/collection/shapelet_based/_rsast.py b/aeon/transformations/collection/shapelet_based/_rsast.py
index 52ccf4e491..32fb2f1605 100644
--- a/aeon/transformations/collection/shapelet_based/_rsast.py
+++ b/aeon/transformations/collection/shapelet_based/_rsast.py
@@ -103,7 +103,7 @@ def __init__(
         n_random_points: int = 10,
         len_method: str = "both",
         nb_inst_per_class: int = 10,
-        seed: int = None,
+        seed: Optional[int] = None,
         n_jobs: int = 1,  # Parllel Processing
     ):
         self.n_random_points = n_random_points
diff --git a/aeon/utils/conversion/_convert_tsf.py b/aeon/utils/conversion/_convert_tsf.py
index 23712cc339..2b5ef3c8b8 100644
--- a/aeon/utils/conversion/_convert_tsf.py
+++ b/aeon/utils/conversion/_convert_tsf.py
@@ -1,5 +1,7 @@
 """Data generators."""
 
+from typing import Optional
+
 __maintainer__ = []
 
 
@@ -9,7 +11,7 @@
 def _convert_tsf_to_hierarchical(
     data: pd.DataFrame,
     metadata: dict,
-    freq: str = None,
+    freq: Optional[str] = None,
     value_column_name: str = "series_value",
 ) -> pd.DataFrame:
     """Convert the data from default_tsf to pd_multiindex_hier.
diff --git a/aeon/utils/datetime.py b/aeon/utils/datetime.py
index 8f366c94cc..1478d86ba4 100644
--- a/aeon/utils/datetime.py
+++ b/aeon/utils/datetime.py
@@ -1,5 +1,7 @@
 """Time format related utilities."""
 
+from typing import Optional
+
 __maintainer__ = []
 __all__ = []
 
@@ -65,7 +67,7 @@ def get_time_index(X):
 
 def _coerce_duration_to_int(
     duration: Union[int, pd.Timedelta, pd.tseries.offsets.BaseOffset, pd.Index],
-    freq: str = None,
+    freq: Optional[str] = None,
 ) -> Union[int, pd.Index]:
     """Coerce durations into integer representations for a given unit of duration.
 
diff --git a/aeon/utils/validation/__init__.py b/aeon/utils/validation/__init__.py
index 3f34bc611c..f0f155567e 100644
--- a/aeon/utils/validation/__init__.py
+++ b/aeon/utils/validation/__init__.py
@@ -1,5 +1,7 @@
 """Validation and checking functions for time series."""
 
+from typing import Optional
+
 __all__ = [
     "is_int",
     "is_float",
@@ -194,7 +196,7 @@ def check_n_jobs(n_jobs: int) -> int:
 
 def check_window_length(
     window_length: ACCEPTED_WINDOW_LENGTH_TYPES,
-    n_timepoints: int = None,
+    n_timepoints: Optional[int] = None,
     name: str = "window_length",
 ) -> NON_FLOAT_WINDOW_LENGTH_TYPES:
     """Validate window length.
diff --git a/aeon/utils/validation/series.py b/aeon/utils/validation/series.py
index f42c684a8b..1465e2f01b 100644
--- a/aeon/utils/validation/series.py
+++ b/aeon/utils/validation/series.py
@@ -1,5 +1,7 @@
 """Functions for checking input data."""
 
+from typing import Optional
+
 __all__ = [
     "check_series",
     "check_time_index",
@@ -305,7 +307,7 @@ def check_series(
 def check_time_index(
     index: Union[pd.Index, np.array],
     allow_empty: bool = False,
-    enforce_index_type: bool = None,
+    enforce_index_type: Optional[bool] = None,
     var_name: str = "input",
 ) -> pd.Index:
     """Check time index.
diff --git a/build_tools/pr_open_commenter.py b/build_tools/pr_open_commenter.py
index 6d7a4d78d8..f64388bf0a 100644
--- a/build_tools/pr_open_commenter.py
+++ b/build_tools/pr_open_commenter.py
@@ -119,6 +119,7 @@
 These checkboxes will add labels to enable/disable CI functionality for this PR. This may not take effect immediately, and a new commit may be required to run the new configuration.
 
 - [ ] Run `pre-commit` checks for all files
+- [ ] Run `mypy` typecheck tests
 - [ ] Run all `pytest` tests and configurations
 - [ ] Run all notebook example tests
 - [ ] Run numba-disabled `codecov` tests
diff --git a/build_tools/pr_welcome_edited.py b/build_tools/pr_welcome_edited.py
index d079713ec5..c402f5b89d 100644
--- a/build_tools/pr_welcome_edited.py
+++ b/build_tools/pr_welcome_edited.py
@@ -40,6 +40,7 @@ def check_label_option(label, option):
 
 label_options = [
     ("full pre-commit", "Run `pre-commit` checks for all files"),
+    ("run typecheck test", "Run `mypy` typecheck tests"),
     ("full pytest actions", "Run all `pytest` tests and configurations"),
     ("full examples run", "Run all notebook example tests"),
     ("codecov actions", "Run numba-disabled `codecov` tests"),
diff --git a/pyproject.toml b/pyproject.toml
index 30b0bad47a..84a308ff65 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -160,6 +160,9 @@ select = ["D"]
 [tool.ruff.lint.pydocstyle]
 convention = "numpy"
 
+[tool.mypy]
+mypy_path = "aeon/"
+
 [tool.pytest.ini_options]
 # ignore certain folders and pytest warnings
 testpaths = "aeon"