Part 4: Local Dev

In Part 3 you wrote integration tests against your deployed stack. But deploying to Cloudflare on every code change is slow. In this part you’ll use alchemy dev to run everything locally with hot reloading.

Start dev mode

alchemy dev

That’s it. Alchemy deploys your stack to the cloud and proxies requests to Workers running locally in workerd. It watches for file changes and hot reloads your Worker automatically.

Your Worker is available at http://localhost:1337 by default:

curl http://localhost:1337/hello.txt

How it works

alchemy dev does three things:

1. Deploys to the cloud — resources like R2 Buckets are created on Cloudflare, while Workers run locally in workerd
2. Watches for changes — when you edit src/worker.ts or any file it imports, the Worker is rebuilt and reloaded instantly
3. Preserves local state — data in your local R2 Bucket persists across restarts

The same alchemy.run.ts is used for both dev and deploy — no separate dev config needed.

Custom port

Set a custom port for your Worker:

src/worker.ts

export default Cloudflare.Worker(
  "Worker",
  {
    main: import.meta.path,
   dev: {
     port: 3000,
   },
  },
  // ...
);

Run tests against dev

Since your Worker runs on localhost in dev mode, you can point your integration tests at it for an even faster feedback loop:

# Terminal 1: start dev mode
alchemy dev

# Terminal 2: run tests against local
bun test test/integ.test.ts

The tests deploy the stack and run HTTP assertions against your local Worker.

Recap

You now have:

• Local development with alchemy dev
• Hot reloading on file changes
• Local emulation of Cloudflare resources

In Part 5, you’ll set up GitHub Actions for automated deployments and PR preview environments.