diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..18c9652
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,38 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+# Cancel superseded runs on the same ref (e.g. rapid pushes to a PR).
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-and-test:
+    name: build & test (node ${{ matrix.node }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        node: [20, 22]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node ${{ matrix.node }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node }}
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Server tests
+        run: npm test
+
+      - name: Web typecheck + build
+        run: npm run build