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JSON Server vs Mock Service Worker: open-source test data and mocking tools compared

Metrics as of , from the GitHub or GitLab API of each repository. Refreshed monthly.

Summary

JSON Server: npm package that serves a REST API with filtering, sorting and pagination from a JSON file.

Mock Service Worker: API mocking library for JavaScript that intercepts requests at the network level in browsers and Node.js.

Both are listed under Test data and mocking. The table gives repository metrics from the GitHub API with their fetch date, then the documented facts used for every comparison in this category, each linked to the README or docs page it comes from. A cell reads "not documented" when the fact was not found in the project's documentation (2 of 10 fact cells here); that does not mean the feature is absent.

Side by side

JSON Server and Mock Service Worker: metrics and documented facts, in the fixed row order used for test data and mocking comparisons.
FactJSON ServerMock Service Worker
Stars75,715118,2161
Forks7,26716261
Contributors9611821
Last release2026-03-2312026-07-081
Last commit2026-03-2312026-09-081
Commits in 90 days01121
LicenseMIT1MIT1
Primary languageJavaScript1TypeScript1
Statusslow1active1
Languages for writing testsnot documentednot found in the project's documentation as of JavaScript source: README
ProtocolsHTTP (REST API routes for GET, POST, PUT, PATCH, DELETE) source: READMEHTTP, GraphQL, WebSocket source: Docs: Quick start
Definition formatJSON or JSON5 data file (db.json or db.json5) source: READMECode (request handlers passed to setupServer in Node.js or setupWorker in the browser) source: Docs: Quick start
Framework integrationsnot documentednot found in the project's documentation as of Vitest (quick start setup) source: Docs: Quick start
Install methodnpm (npm install json-server) source: READMEnpm (npm i msw --save-dev) source: Docs: Quick start

1 Fetched from the GitHub or GitLab API on . Hover a value for its own date.

When each fits

Written from each project's documented scope, not from preference. Neither tool is ranked.

JSON Server

Fits projects that need a REST API served from a JSON data file; its README describes query parameters for conditions, sorting, pagination and embedded relations. source: README

Mock Service Worker

Fits projects that mock APIs in the browser and in Node.js; its docs describe intercepting outgoing requests and answering them with mocked responses. source: Docs: Introduction

More on these tools

Sources

  1. GitHub REST API: repository, read
  2. GitHub REST API: repository, read
  3. GitHub REST API: contributors, read
  4. GitHub REST API: contributors, read
  5. GitHub REST API: latest release, read
  6. GitHub REST API: latest release, read
  7. GitHub REST API: commits, read
  8. GitHub REST API: commits, read
  9. README, read
  10. README, read
  11. Docs: Quick start, read
  12. Docs: Introduction, read

Documented facts collected 2026-09-22. See the methodology for how metrics and facts are gathered.