Gathering detailed insights and metrics for msw
Gathering detailed insights and metrics for msw
Installations
npm install mswDeveloper Guide
BETA
Typescript
Yes
Module System
CommonJS, ESM
Min. Node Version
>=18
Node Version
20.19.3
NPM Version
10.8.2
Releases
232
Languages
4
TypeScript
JavaScript
HTML
Shell
TypeScript (96.65%)
JavaScript (2.95%)
HTML (0.29%)
Shell (0.1%)
Developer
Download Statistics
Total Downloads
0
Last Day
0
Last Week
0
Last Month
0
Last Year
0
GitHub Statistics
MIT License
16,901 Stars
1,653 Commits
553 Forks
62 Watchers
25 Branches
167 Contributors
Updated on Jul 13, 2025
Sponsor this package
Maintainers
1
Package Meta Information
Latest Version
2.10.4
Package Id
msw@2.10.4
Unpacked Size
4.32 MB
Size
881.80 kB
File Count
559
NPM Version
10.8.2
Node Version
20.19.3
Published on
Jul 12, 2025
Total Downloads
Cumulative downloads
Total Downloads
NaN
Last Day
0%
NaN
Compared to previous day
Last Week
0%
NaN
Compared to previous week
Last Month
0%
NaN
Compared to previous month
Last Year
0%
NaN
Compared to previous year
Weekly Downloads
Monthly Downloads
Yearly Downloads
Dependencies
18
@bundled-es-modules/cookie@bundled-es-modules/statuses@bundled-es-modules/tough-cookie@inquirer/confirm@mswjs/interceptors@open-draft/deferred-promise@open-draft/until@types/cookie@types/statusesgraphqlheaders-polyfillis-node-processoutvariantpath-to-regexppicocolorsstrict-event-emittertype-festyargs
Peer Dependencies
1
Dev Dependencies
47
@commitlint/cli@commitlint/config-conventional@fastify/websocket@open-draft/test-server@ossjs/release@playwright/test@types/express@types/json-bigint@types/node@types/serviceworker@typescript-eslint/eslint-plugin@typescript-eslint/parser@web/dev-serveraxiosbabel-minifycommitizencross-envcross-fetchcz-conventional-changelogesbuildesbuild-loadereslinteslint-config-prettiereslint-plugin-prettierexpressfastifyfs-teardownglobjsdomjson-bigintkniplint-stagedpage-withprettierpublintregenerator-runtimerimrafsimple-git-hookstsuptypescriptundiciurl-loadervitestvitest-environment-miniflarewebpackwebpack-http-servermsw
Mock Service Worker
Industry standard API mocking for JavaScript.
Features
- Seamless. A dedicated layer of requests interception at your disposal. Keep your application's code and tests unaware of whether something is mocked or not.
- Deviation-free. Request the same production resources and test the actual behavior of your app. Augment an existing API, or design it as you go when there is none.
- Familiar & Powerful. Use Express-like routing syntax to intercept requests. Use parameters, wildcards, and regular expressions to match requests, and respond with necessary status codes, headers, cookies, delays, or completely custom resolvers.
"I found MSW and was thrilled that not only could I still see the mocked responses in my DevTools, but that the mocks didn't have to be written in a Service Worker and could instead live alongside the rest of my app. This made it silly easy to adopt. The fact that I can use it for testing as well makes MSW a huge productivity booster."
Documentation
This README will give you a brief overview of the library, but there's no better place to start with Mock Service Worker than its official documentation.
Examples
- See the list of Usage examples
Courses
We've partnered with Egghead to bring you quality paid materials to learn the best practices of API mocking on the web. Please give them a shot! The royalties earned from them help sustain the project's development. Thank you.
- 🚀 Mocking REST and GraphQL APIs with Mock Service Worker
- 🔌 Mocking (and testing) WebSocket APIs with Mock Service Worker
Browser
How does it work?
In-browser usage is what sets Mock Service Worker apart from other tools. Utilizing the Service Worker API, which can intercept requests for the purpose of caching, Mock Service Worker responds to intercepted requests with your mock definition on the network level. This way your application knows nothing about the mocking.
Take a look at this quick presentation on how Mock Service Worker functions in a browser:
How is it different?
- This library intercepts requests on the network level, which means after they have been performed and "left" your application. As a result, the entirety of your code runs, giving you more confidence when mocking;
- Imagine your application as a box. Every API mocking library out there opens your box and removes the part that does the request, placing a blackbox in its stead. Mock Service Worker leaves your box intact, 1-1 as it is in production. Instead, MSW lives in a separate box next to yours;
- No more stubbing of
fetch,axios,react-query, you-name-it; - You can reuse the same mock definition for the unit, integration, and E2E testing. Did we mention local development and debugging? Yep. All running against the same network description without the need for adapters or bloated configurations.
Usage example
1// 1. Import the library. 2import { http, HttpResponse } from 'msw' 3import { setupWorker } from 'msw/browser' 4 5// 2. Describe network behavior with request handlers. 6const worker = setupWorker( 7 http.get('https://github.com/octocat', ({ request, params, cookies }) => { 8 return HttpResponse.json( 9 { 10 message: 'Mocked response', 11 }, 12 { 13 status: 202, 14 statusText: 'Mocked status', 15 }, 16 ) 17 }), 18) 19 20// 3. Start mocking by starting the Service Worker. 21await worker.start()
Performing a GET https://github.com/octocat request in your application will result into a mocked response that you can inspect in your browser's "Network" tab:
Tip: Did you know that although Service Worker runs in a separate thread, your request handlers execute entirely on the client? This way you can use the same languages, like TypeScript, third-party libraries, and internal logic to create the mocks you need.
Node.js
How does it work?
There's no such thing as Service Workers in Node.js. Instead, MSW implements a low-level interception algorithm that can utilize the very same request handlers you have for the browser. This blends the boundary between environments, allowing you to focus on your network behaviors.
How is it different?
- Does not stub
fetch,axios, etc. As a result, your tests know nothing about mocking; - You can reuse the same request handlers for local development and debugging, as well as for testing. Truly a single source of truth for your network behavior across all environments and all tools.
Usage example
Here's an example of using Mock Service Worker while developing your Express server:
1import express from 'express' 2import { http, HttpResponse } from 'msw' 3import { setupServer } from 'msw/node' 4 5const app = express() 6const server = setupServer() 7 8app.get( 9 '/checkout/session', 10 server.boundary((req, res) => { 11 // Describe the network for this Express route. 12 server.use( 13 http.get( 14 'https://api.stripe.com/v1/checkout/sessions/:id', 15 ({ params }) => { 16 return HttpResponse.json({ 17 id: params.id, 18 mode: 'payment', 19 status: 'open', 20 }) 21 }, 22 ), 23 ) 24 25 // Continue with processing the checkout session. 26 handleSession(req, res) 27 }), 28)
This example showcases
server.boundary()to scope request interception to a particular closure, which is extremely handy!
Sponsors
Mock Service Worker is trusted by hundreds of thousands of engineers around the globe. It's used by companies like Google, Microsoft, Spotify, Amazon, Netflix, and countless others. Despite that, it remains a hobby project maintained in a spare time and has no opportunity to financially support even a single full-time contributor.
You can change that! Consider sponsoring the effort behind one of the most innovative approaches around API mocking. Raise a topic of open source sponsorships with your boss and colleagues. Let's build sustainable open source together!
Golden sponsors
Become our golden sponsor and get featured right here, enjoying other perks like issue prioritization and a personal consulting session with us.
Learn more on our GitHub Sponsors profile.
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Silver sponsors
Become our silver sponsor and get your profile image and link featured right here.
Learn more on our GitHub Sponsors profile.
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Bronze sponsors
Become our bronze sponsor and get your profile image and link featured in this section.
Learn more on our GitHub Sponsors profile.
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Awards & mentions
We've been extremely humbled to receive awards and mentions from the community for all the innovation and reach Mock Service Worker brings to the JavaScript ecosystem.
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Solution Worth PursuingTechnology Radar (2020–2021) |
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The Most Exciting Use of TechnologyOpen Source Awards (2020) |
No vulnerabilities found.
Reason
30 commit(s) and 23 issue activity found in the last 90 days -- score normalized to 10
Reason
no dangerous workflow patterns detected
Reason
no binaries found in the repo
Reason
license file detected
Details
- Info: project has a license file: LICENSE.md:0
- Info: FSF or OSI recognized license: MIT License: LICENSE.md:0
Reason
Found 3/30 approved changesets -- score normalized to 1
Reason
no effort to earn an OpenSSF best practices badge detected
Reason
detected GitHub workflow tokens with excessive permissions
Details
- Info: jobLevel 'contents' permission set to 'read': .github/workflows/release.yml:12
- Warn: no topLevel permission defined: .github/workflows/auto.yml:1
- Warn: no topLevel permission defined: .github/workflows/ci.yml:1
- Warn: no topLevel permission defined: .github/workflows/compat.yml:1
- Warn: no topLevel permission defined: .github/workflows/release-preview.yml:1
- Warn: no topLevel permission defined: .github/workflows/release.yml:1
- Warn: no topLevel permission defined: .github/workflows/smoke-test.yml:1
- Warn: no topLevel permission defined: .github/workflows/typescript-nightly.yml:1
- Info: no jobLevel write permissions found
Reason
dependency not pinned by hash detected -- score normalized to 0
Details
- Info: Possibly incomplete results: error parsing shell code: invalid parameter name: .github/workflows/typescript-nightly.yml:62
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/auto.yml:10: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/auto.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:155: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:158: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:163: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:169: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:188: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:191: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:196: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:213: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:216: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:221: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:227: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:245: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:256: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:259: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:264: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:270: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:15: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:18: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:23: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:38: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:50: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:53: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
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- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:86: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:89: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:94: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:100: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:122: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/ci.yml:125: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:130: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/ci.yml:136: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/ci.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/compat.yml:60: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/compat.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/compat.yml:63: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/compat.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/compat.yml:67: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/compat.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/compat.yml:15: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/compat.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/compat.yml:18: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/compat.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/compat.yml:23: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/compat.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/lock-closed-issues.yml:14: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/lock-closed-issues.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/release-preview.yml:17: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/release-preview.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/release-preview.yml:20: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/release-preview.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/release-preview.yml:25: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/release-preview.yml/main?enable=pin
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- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/release.yml:22: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/release.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/release.yml:29: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/release.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/smoke-test.yml:18: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/smoke-test.yml/main?enable=pin
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- Warn: third-party GitHubAction not pinned by hash: .github/workflows/smoke-test.yml:26: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/smoke-test.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/typescript-nightly.yml:14: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/typescript-nightly.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/typescript-nightly.yml:40: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/typescript-nightly.yml/main?enable=pin
- Warn: GitHub-owned GitHubAction not pinned by hash: .github/workflows/typescript-nightly.yml:43: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/typescript-nightly.yml/main?enable=pin
- Warn: third-party GitHubAction not pinned by hash: .github/workflows/typescript-nightly.yml:48: update your workflow using https://app.stepsecurity.io/secureworkflow/mswjs/msw/typescript-nightly.yml/main?enable=pin
- Info: 0 out of 37 GitHub-owned GitHubAction dependencies pinned
- Info: 0 out of 16 third-party GitHubAction dependencies pinned
Reason
project is not fuzzed
Details
- Warn: no fuzzer integrations found
Reason
security policy file not detected
Details
- Warn: no security policy file detected
- Warn: no security file to analyze
- Warn: no security file to analyze
- Warn: no security file to analyze
Reason
SAST tool is not run on all commits -- score normalized to 0
Details
- Warn: 0 commits out of 17 are checked with a SAST tool
Reason
28 existing vulnerabilities detected
Details
- Warn: Project is vulnerable to: GHSA-28mc-g557-92m7
- Warn: Project is vulnerable to: GHSA-968p-4wvh-cqc8
- Warn: Project is vulnerable to: GHSA-jr5f-v2jv-69x6
- Warn: Project is vulnerable to: GHSA-qwcr-r2fm-qrc7
- Warn: Project is vulnerable to: GHSA-v6h2-p8h4-qcjw
- Warn: Project is vulnerable to: GHSA-pxg6-pf52-xh8x
- Warn: Project is vulnerable to: GHSA-3xgq-45jj-v275
- Warn: Project is vulnerable to: GHSA-67mh-4wv8-2f99
- Warn: Project is vulnerable to: GHSA-qw6h-vgh9-j6wx
- Warn: Project is vulnerable to: GHSA-593f-38f6-jp5m
- Warn: Project is vulnerable to: GHSA-x2rg-q646-7m2v
- Warn: Project is vulnerable to: GHSA-mwcw-c2x4-8c55
- Warn: Project is vulnerable to: GHSA-9wv6-86v2-598j
- Warn: Project is vulnerable to: GHSA-rhx6-c78j-4q9w
- Warn: Project is vulnerable to: GHSA-m6fv-jmcg-4jfg
- Warn: Project is vulnerable to: GHSA-cm22-4g7w-348p
- Warn: Project is vulnerable to: GHSA-c76h-2ccp-4975
- Warn: Project is vulnerable to: GHSA-cxrh-j4jr-qwg3
- Warn: Project is vulnerable to: GHSA-64vr-g452-qvp3
- Warn: Project is vulnerable to: GHSA-9cwx-2883-4wfx
- Warn: Project is vulnerable to: GHSA-vg6x-rcgg-rjx6
- Warn: Project is vulnerable to: GHSA-x574-m823-4x7w
- Warn: Project is vulnerable to: GHSA-4r4m-qw57-chr8
- Warn: Project is vulnerable to: GHSA-xcj6-pq6g-qj4x
- Warn: Project is vulnerable to: GHSA-356w-63v5-8wf4
- Warn: Project is vulnerable to: GHSA-859w-5945-r5v3
- Warn: Project is vulnerable to: GHSA-3h5v-q93c-6h6q
- Warn: Project is vulnerable to: GHSA-p9pc-299p-vxgp
Score
3.9
/10
Last Scanned on 2025-07-07
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