diff --git a/justfile b/justfile
new file mode 100644
index 0000000..82986ab
--- /dev/null
+++ b/justfile
@@ -0,0 +1,40 @@
+# github-warden task runner.
+# Run `just` (or `just --list`) to see available recipes.
+
+set quiet
+
+# List recipes
+default:
+    @just --list
+
+# Type-check (no emit)
+tsc:
+    npx tsc --noEmit
+
+# Run the test suite (optionally pass a path/pattern: `just test diff`)
+test *args:
+    npx vitest run {{args}}
+
+# Run tests in watch mode
+test-watch:
+    npx vitest
+
+# Build the CLI bundle (dist/cli.js)
+build:
+    npm run build
+
+# Build the GitHub Action bundle (action/index.mjs)
+build-action:
+    npm run build:action
+
+# Everything CI's `check` job runs: typecheck, tests, action bundle freshness
+check: tsc test build-action
+    git diff --exit-code action/index.mjs
+
+# Dogfood: audit our own config with chant (CI's `dogfood-audit` job)
+audit:
+    npx chant audit . --fail-on merge-worthy
+
+# Install dependencies (clean, lockfile-faithful)
+install:
+    npm ci