---
title: Handlers · Cloudflare Workers docs
description: Methods, such as `fetch()`, on Workers that can receive and process external inputs.
lastUpdated: 2024-08-13T19:56:56.000Z
source_url:
  html: https://3fb19f37.preview.developers.cloudflare.com/workers/runtime-apis/handlers/index.md
  md: https://3fb19f37.preview.developers.cloudflare.com/workers/runtime-apis/handlers/
---

Handlers are methods on Workers that can receive and process external inputs, and can be invoked from outside your Worker. For example, the `fetch()` handler receives an HTTP request, and can return a response:

```js
export default {
  async fetch(request, env, ctx) {
    return new Response('Hello World!');
  },
};
```

The following handlers are available within Workers:

* [Alarm Handler](https://developers.cloudflare.com/durable-objects/api/alarms/)
* [Email Handler](https://developers.cloudflare.com/email-routing/email-workers/runtime-api/)
* [Fetch Handler](https://developers.cloudflare.com/workers/runtime-apis/handlers/fetch/)
* [Queue Handler](https://developers.cloudflare.com/queues/configuration/javascript-apis/#consumer)
* [Scheduled Handler](https://developers.cloudflare.com/workers/runtime-apis/handlers/scheduled/)
* [Tail Handler](https://developers.cloudflare.com/workers/runtime-apis/handlers/tail/)

## Handlers in Python Workers

When you [write Workers in Python](https://developers.cloudflare.com/workers/languages/python/), handlers are prefixed with `on_`. For example, `on_fetch` or `on_scheduled`.
