# Hot reload an HTTP server

The [`--hot`](/runtime/watch-mode#hot-mode) flag runs a file with hot reloading enabled. When any module or file changes, Bun re-runs the file.

```sh terminal icon="terminal"
bun --hot run index.ts
```

---

Bun detects when you are running an HTTP server with `Bun.serve()`. It reloads your fetch handler when source files change, _without_ restarting the `bun` process. This makes hot reloads nearly instantaneous.

<Note>
Hot reloading doesn't reload the page in your browser.
</Note>
 
```ts index.ts icon="/icons/typescript.svg"
Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello world");
  },
});
```