diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..0131ec8
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,36 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  build-typecheck-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      # Builds packages/* so their dist/ output exists before anything
+      # (including apps/web) typechecks against them.
+      - name: Build packages
+        run: pnpm run build
+
+      - name: Typecheck
+        run: pnpm run typecheck
+
+      - name: Test
+        run: pnpm run test
+
+      - name: Build web app
+        run: pnpm --filter @custos/web build