Mock Service Worker

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About

Mock Service Worker is ranked #12 of 27 in API mocking tools on Inferse. It runs on Self-hosted, Web.

Compared on API mocking tools

Free plan: Yesmswjs.io
Dynamic responses: Yesmswjs.io
OpenAPI import: Yesmswjs.io
Local deployment: Yesmswjs.io
Supported protocols: HTTP, REST, GraphQL, WebSocket, SSEmswjs.io

Facts

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.mswjs.io · 30 Sept 2026
Network APIs: MSW supports mocking REST, GraphQL, Server-Sent Events, and WebSocket APIs.mswjs.io · 30 Sept 2026
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.mswjs.io · 30 Sept 2026
Request clients: MSW works with native fetch and third-party clients such as Axios, React Query, and Apollo.mswjs.io · 30 Sept 2026
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.mswjs.io · 30 Sept 2026
Node.js integration: In Node.js, MSW provides setupServer for enabling API mocking in an application process or test runner.mswjs.io · 30 Sept 2026
Tool integrations: The site provides integration guides for Cloudflare, React Native, Storybook, Vite, and Vitest, as well as browser and Node.js.mswjs.io · 30 Sept 2026
Open source: The project describes MSW as open-source and free to try.mswjs.io · 30 Sept 2026
Paid learning: The documentation says its official Egghead courses require a paid subscription.mswjs.io · 30 Sept 2026
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.mswjs.io · 30 Sept 2026
Node.js limitation: MSW cannot intercept requests made directly through net.connect() or net.createConnection(), which some libraries use.mswjs.io · 30 Sept 2026
Support: The project directs users to its debugging runbook, Discord, and GitHub discussions for help.source.mswjs.io · 30 Sept 2026
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.mswjs.io · 30 Sept 2026
Network standards: MSW uses the Fetch API to handle intercepted requests and construct mocked responses, including requests made with other clients.mswjs.io · 30 Sept 2026
Protocols: MSW supports mocking HTTP, GraphQL, Server-Sent Events, and WebSocket APIs.mswjs.io · 30 Sept 2026
Reusable mocks: The same mock handlers can be reused for development, integration and end-to-end testing, Storybook, and live demos.mswjs.io · 30 Sept 2026
Client compatibility: The documentation names native fetch and third-party clients including Axios, React Query, and Apollo as supported request clients.mswjs.io · 30 Sept 2026
Browser integration: In browsers, MSW uses the Service Worker API to intercept requests at the network level.mswjs.io · 30 Sept 2026
Node integration: In Node.js, MSW intercepts raw socket connections before they reach the network code written in C.mswjs.io · 30 Sept 2026
Additional integrations: The MSW organization lists extensions for Playwright, Storybook, Cloudflare workerd, and SvelteKit.github.com · 30 Sept 2026
Limitations: MSW's GraphQL documentation says it supports queries and mutations, while subscriptions are described as coming in the future.mswjs.io · 30 Sept 2026
Support: The quick start directs users to a debugging runbook, MSW Discord, and GitHub Discussions for help.mswjs.io · 30 Sept 2026
Learning resources: The documentation says its official Egghead courses require a paid subscription and help support the project.mswjs.io · 30 Sept 2026