Mock Service Worker

6.2easy start · #17 of 27
in API Mocking Tools

Free to practise onnot on record
Free trialnot on record
Well documentedyes
Runs where you worknot on record

Runs on self-hosted, Web.

Visit site Alternatives

Mock Service Worker is ranked #17 of 27 in API mocking tools on The Geeks Club. It runs on Self-hosted, Web.

Compared on API mocking tools

Free plan: Yes
Dynamic responses: Yes
OpenAPI import: Yes
Local deployment: Yes
Supported protocols: HTTP, REST, GraphQL, WebSocket, SSE

Best Mock Service Worker alternatives

See all 20

WireMock 0 of 4 in the starter kit Lesson 17.8 WireMock 0 of 4 in the starter kit Lesson 27.6 Microcks 0 of 4 in the starter kit Lesson 37.4 Mockzilla 0 of 4 in the starter kit Lesson 47.4 Parasoft SOAtest 0 of 4 in the starter kit Lesson 57.3 Knockout API 0 of 4 in the starter kit Lesson 67.2

The record

Purpose: Mock Service Worker (MSW) is an API mocking library for browser and Node.js that intercepts outgoing requests so developers can observe and respond with mocked responses.
Network APIs: MSW supports mocking REST, GraphQL, Server-Sent Events, and WebSocket APIs.
Shared mocks: The same client-agnostic mocks can be reused across frameworks, tools, and environments, including development, integration and end-to-end testing, Storybook, and live demos.
Request clients: MSW works with native fetch and third-party clients such as Axios, React Query, and Apollo.
Browser integration: In browsers, MSW registers a Service Worker to intercept requests at the network level; the worker script must be served by the application.
Node.js integration: In Node.js, MSW provides setupServer for enabling API mocking in an application process or test runner.
Tool integrations: The site provides integration guides for Cloudflare, React Native, Storybook, Vite, and Vitest, as well as browser and Node.js.
Open source: The project describes MSW as open-source and free to try.
Paid learning: The documentation says its official Egghead courses require a paid subscription.
Browser limitation: Because browser interception relies on the Service Worker API, browser-specific limitations apply; the docs also state that Firefox does not notify the worker about page XMLHttpRequest requests.
Node.js limitation: MSW cannot intercept requests made directly through net.connect() or net.createConnection(), which some libraries use.
Support: The project directs users to its debugging runbook, Discord, and GitHub discussions for help.
What it does: MSW is an API mocking library for browser and Node.js that intercepts outgoing requests so they can be observed and answered with mocked responses.
Network standards: MSW uses the Fetch API to handle intercepted requests and construct mocked responses, including requests made with other clients.

Where it ranks on The Geeks Club

Best API Mocking Tools in 2026#17 of 27

Is Mock Service Worker yours?

Claim it for free: prove the domain, then correct facts, plans and screenshots. An editor reviews every change.

Claim it free Promote Mock Service Worker

Sources

mswjs.io/docs/· checked 30 Sept 2026
mswjs.io· checked 30 Sept 2026
mswjs.io/docs/integrations/browser· checked 30 Sept 2026
mswjs.io/docs/integrations/node· checked 30 Sept 2026
mswjs.io/docs/limitations· checked 30 Sept 2026
source.mswjs.io/docs/quick-start· checked 30 Sept 2026
mswjs.io/docs· checked 30 Sept 2026
mswjs.io/docs/http· checked 30 Sept 2026
github.com/mswjs· checked 30 Sept 2026
mswjs.io/docs/graphql· checked 30 Sept 2026