> ## Documentation Index
> Fetch the complete documentation index at: https://bun.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Error Handling

> Learn how to handle errors in Bun's development server

To activate development mode, set `development: true`.

```ts title="server.ts" icon="https://mintcdn.com/bun-1dd33a4e/JUhaF6Mf68z_zHyy/icons/typescript.svg?fit=max&auto=format&n=JUhaF6Mf68z_zHyy&q=85&s=7ac549adaea8d5487d8fbd58cc3ea35b" theme={"theme":{"light":"github-light","dark":"dracula"}}
Bun.serve({
  development: true, // [!code ++]
  fetch(req) {
    throw new Error("woops!");
  },
});
```

In development mode, Bun will surface errors in-browser with a built-in error page.

<Frame>
  <img src="https://mintcdn.com/bun-1dd33a4e/PY1574V41bdK8wNs/images/exception_page.png?fit=max&auto=format&n=PY1574V41bdK8wNs&q=85&s=26f9bec162e97288f1f0d736773b2b6e" alt="Bun's built-in 500 page" width="800" height="579" data-path="images/exception_page.png" />
</Frame>

### `error` callback

To handle server-side errors, implement an `error` handler. This function should return a `Response` to serve to the client when an error occurs. This response will supersede Bun's default error page in `development` mode.

```ts theme={"theme":{"light":"github-light","dark":"dracula"}}
Bun.serve({
  fetch(req) {
    throw new Error("woops!");
  },
  error(error) {
    return new Response(`<pre>${error}\n${error.stack}</pre>`, {
      headers: {
        "Content-Type": "text/html",
      },
    });
  },
});
```

<Info>[Learn more about debugging in Bun](/runtime/debugger)</Info>