diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..e58cf16
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,141 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  lint:
+    name: Lint (Ruff)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install ruff
+      - name: Run Ruff
+        run: ruff check .
+
+  test-linux:
+    name: Test (Linux)
+    needs: lint
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ['3.10', '3.11', '3.12']
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install pytest
+          pip install -e .
+      - name: Run tests
+        run: pytest
+
+  test-windows:
+    name: Test (Windows)
+    needs: lint
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        python-version: ['3.10', '3.11', '3.12']
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install pytest
+          pip install -e .
+      - name: Run tests
+        run: pytest
+
+  test-macos:
+    name: Test (macOS)
+    needs: lint
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        python-version: ['3.10', '3.11', '3.12']
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install pytest
+          pip install -e .
+      - name: Run tests
+        run: pytest
+
+  build-linux:
+    name: Build (Linux)
+    needs: test-linux
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install build
+      - name: Build package
+        run: python -m build
+
+  build-windows:
+    name: Build (Windows)
+    needs: test-windows
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install build
+      - name: Build package
+        run: python -m build
+
+  build-macos:
+    name: Build (macOS)
+    needs: test-macos
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install build
+      - name: Build package
+        run: python -m build
diff --git a/requirements-dev.txt b/requirements-dev.txt
new file mode 100644
index 0000000..2327f42
--- /dev/null
+++ b/requirements-dev.txt
@@ -0,0 +1,4 @@
+pytest
+ruff
+build
+twine
diff --git a/tests/test_ai.py b/tests/test_ai.py
new file mode 100644
index 0000000..a9db973
--- /dev/null
+++ b/tests/test_ai.py
@@ -0,0 +1,38 @@
+from shellmind.ai import _int_env, _trim_history, _direct_shell_command, _trim_tool_output, config
+
+def test_int_env(monkeypatch):
+    monkeypatch.setenv("TEST_VAR", "10")
+    assert _int_env("TEST_VAR", 5, minimum=2) == 10
+
+    monkeypatch.setenv("TEST_VAR", "1")
+    assert _int_env("TEST_VAR", 5, minimum=2) == 2
+
+    monkeypatch.setenv("TEST_VAR", "invalid")
+    assert _int_env("TEST_VAR", 5, minimum=2) == 5
+
+    monkeypatch.delenv("TEST_VAR", raising=False)
+    assert _int_env("TEST_VAR", 5, minimum=2) == 5
+
+def test_trim_history():
+    messages = [{"role": "user", "parts": [{"text": "hello"}]}] * 10
+    # config.max_history_messages is 6 by default
+    _trim_history(messages)
+    assert len(messages) <= config.max_history_messages
+
+def test_direct_shell_command():
+    assert _direct_shell_command("!ls") == "ls"
+    assert _direct_shell_command("/shell echo hi") == "echo hi"
+    assert _direct_shell_command("/run git status") == "git status"
+    assert _direct_shell_command("just text") is None
+
+def test_trim_tool_output():
+    text = "a" * 2000
+    trimmed = _trim_tool_output(text)
+    assert "truncated" in trimmed
+    assert len(trimmed) < 2000
+
+    short_text = "hello"
+    assert _trim_tool_output(short_text) == "hello"
+
+    empty_text = ""
+    assert _trim_tool_output(empty_text) == "(no output)"