> ## Documentation Index
> Fetch the complete documentation index at: https://bun-1dd33a4e-farm-ad2450b3-transpiler-cache-version-namespa.mintlify.site/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-farm-ad2450b3-transpiler-cache-version-namespa/pVrMBuZvntvIe2NO/icons/typescript.svg?fit=max&auto=format&n=pVrMBuZvntvIe2NO&q=85&s=81fcaf3ac2cead5d758f3588a492f46a" theme={"theme":{"light":"github-light","dark":"dracula"}}
Bun.serve({
  development: true, // [!code ++]
  fetch(req) {
    throw new Error("woops!");
  },
});
```

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

<Frame>
  <img src="https://mintcdn.com/bun-1dd33a4e-farm-ad2450b3-transpiler-cache-version-namespa/pVrMBuZvntvIe2NO/images/exception_page.png?fit=max&auto=format&n=pVrMBuZvntvIe2NO&q=85&s=3fe4b047b49d2b923c70d28ad8bea465" 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. Return a `Response` to serve to the client when an error occurs. In `development` mode, this response replaces Bun's default error page.

```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>