diff --git a/.github/workflows/python-app.yml b/.github/workflows/python-app.yml
index e8bdc6e..2630c41 100644
--- a/.github/workflows/python-app.yml
+++ b/.github/workflows/python-app.yml
@@ -19,14 +19,15 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-    - name: Set up Python 3.10
+    - name: Set up Python 3.12
       uses: actions/setup-python@v3
       with:
         python-version: "3.12"
+        cache: 'pip' # caching pip dependencies
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install flake8 pytest
+        pip install flake8 pytest mypy
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: Lint with flake8
       run: |
@@ -34,6 +35,12 @@ jobs:
         flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+    - name: Run mypy
+      uses: sasanquaneuf/mypy-github-action@releases/v1
+      with:
+        checkName: 'build'   # NOTE: this needs to be the same as the job name
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     - name: Test with pytest
       run: |
         pytest
diff --git a/README.md b/README.md
index 7b56303..44b9591 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,7 @@ jupyter lab
 - https://github.com/miguelrizzog96/Queue_Simulation_Python/blob/master/server.ipynb
 - https://notebook.community/xunilrj/sandbox/courses/IMTx-Queue-Theory/Week2_Lab_MM1
 - https://github.com/eveneveno/MMC_queue
+- https://github.com/miguelrizzog96/Queue_Simulation_Python
 
 ## Distributions
 - https://numpy.org/doc/stable/reference/random/generated/numpy.random.exponential.html
diff --git a/src/queue.py b/src/queue.py
index 271a7fe..54bd249 100644
--- a/src/queue.py
+++ b/src/queue.py
@@ -7,7 +7,7 @@ def __init__(self, inter_arrival_times, execution_times, executors=1) -> None:
         self.__execution_times = execution_times
         self.__departure_times = np.empty_like(inter_arrival_times)
         self.__wait_times = np.empty_like(inter_arrival_times)
-        self.__utilization_by_executor = {
+        self.__utilization_by_executor: dict[int, list[float]] = {
             executor_id: []
             for executor_id in range(0, executors)
         }