---
title: 🕸 Web Standards · Cloudflare Workers docs
description: When using the API, Miniflare allows you to substitute custom Responses for
fetch() calls using undici's
MockAgent API.
This is useful for testing Workers that make HTTP requests to other services. To
enable fetch mocking, create a
MockAgent
using the createFetchMock() function, then set this using the fetchMock
option.
lastUpdated: 2024-12-18T20:15:16.000Z
source_url:
  html: https://zt-dark-mode-changelog.preview.developers.cloudflare.com/workers/testing/miniflare/core/standards/index.md
  md: https://zt-dark-mode-changelog.preview.developers.cloudflare.com/workers/testing/miniflare/core/standards/
---

* [Web Standards Reference](https://developers.cloudflare.com/workers/runtime-apis/web-standards)
* [Encoding Reference](https://developers.cloudflare.com/workers/runtime-apis/encoding)
* [Fetch Reference](https://developers.cloudflare.com/workers/runtime-apis/fetch)
* [Request Reference](https://developers.cloudflare.com/workers/runtime-apis/request)
* [Response Reference](https://developers.cloudflare.com/workers/runtime-apis/response)
* [Streams Reference](https://developers.cloudflare.com/workers/runtime-apis/streams)
* [Web Crypto Reference](https://developers.cloudflare.com/workers/runtime-apis/web-crypto)

## Mocking Outbound `fetch` Requests

When using the API, Miniflare allows you to substitute custom `Response`s for `fetch()` calls using `undici`'s [`MockAgent` API](https://undici.nodejs.org/#/docs/api/MockAgent?id=mockagentgetorigin). This is useful for testing Workers that make HTTP requests to other services. To enable `fetch` mocking, create a [`MockAgent`](https://undici.nodejs.org/#/docs/api/MockAgent?id=mockagentgetorigin) using the `createFetchMock()` function, then set this using the `fetchMock` option.

```js
import { Miniflare, createFetchMock } from "miniflare";


// Create `MockAgent` and connect it to the `Miniflare` instance
const fetchMock = createFetchMock();
const mf = new Miniflare({
  modules: true,
  script: `
  export default {
    async fetch(request, env, ctx) {
      const res = await fetch("https://example.com/thing");
      const text = await res.text();
      return new Response(\`response:\${text}\`);
    }
  }
  `,
  fetchMock,
});


// Throw when no matching mocked request is found
// (see https://undici.nodejs.org/#/docs/api/MockAgent?id=mockagentdisablenetconnect)
fetchMock.disableNetConnect();


// Mock request to https://example.com/thing
// (see https://undici.nodejs.org/#/docs/api/MockAgent?id=mockagentgetorigin)
const origin = fetchMock.get("https://example.com");
// (see https://undici.nodejs.org/#/docs/api/MockPool?id=mockpoolinterceptoptions)
origin
  .intercept({ method: "GET", path: "/thing" })
  .reply(200, "Mocked response!");


const res = await mf.dispatchFetch("http://localhost:8787/");
console.log(await res.text()); // "response:Mocked response!"
```

## Subrequests

Miniflare does not support limiting the amount of [subrequests](https://developers.cloudflare.com/workers/platform/limits#account-plan-limits). Please keep this in mind if you make a large amount of subrequests from your Worker.
