For frontend devs and QA engineers who can't wait on the backend

Mock any API response.
Directly in DevTools._

The backend isn't returning what you need. You can't change it. Configure the mock in JediMock, paste one script in the console. The next request is intercepted — no service worker, no proxy, no certificate, no cleanup. Zero footprint in your app. Zero trace when you're done.

Try it free — no account View on GitHub
DevTools — Console
// paste the script. that's it. ⚡ JediMock active { url: '/api/users/*', mode: 'Merge' } // your app makes requests as normal ⚡ JediMock intercepted { url: '/api/users/42', status: 200 } // refresh the page — mock is gone, real API is back >
JediMock demo — configure a mock, generate a script, paste in DevTools

When you need it

Test edge cases without backend help
Force a 401, an empty list, a timeout, or a specific error — without touching the server.
QA regression flows without a real environment
Run the same auth retry, error recovery, or empty-state scenario every time — deterministically.
Demo features before the API exists
Design reviews and stakeholder demos don't wait for backend sprints.
Reproduce a bug from production data
Paste the real response, edit the one field that triggers the bug, done.
Test async flows and polling
Async ID mode captures a dynamic ID from one request and injects it into the next — no callback server needed.
QA slow responses and timeouts
Add artificial delay, trigger fallback mode, or simulate a server that never responds — all without coordinating with anyone.

JediMock intercepts both fetch and XMLHttpRequest at the browser level — no changes to your app, no service worker registered, no proxy process running. Wildcards work: /api/users/* catches every user endpoint in one script. Merge changes on top of the real response or replace it entirely.

Need more control? Response Rules let you return different data on specific call counts — 401 on the first hit, 200 after, exactly like a real auth retry flow. Perfect for QA regression scripts that need to reproduce the same sequence every time. Fallback mode fires the mock automatically if the server doesn't respond within your timeout. Async ID mode captures a job ID from a trigger request and replaces the placeholder in your polling response — no real callback server needed.

Refresh the page and the mock is gone. The real API comes back. Nothing to undo.

vs. MSW, Mockoon, Charles, Proxyman — for devs and QA

Other tools
JediMock
Requires a service worker in your codebase
Zero footprint in your app
Proxy server or daemon running locally
Nothing running except your browser
HTTPS certificate to install and trust
Paste a script. Done.
Config files or a server process to maintain
Session persists in the browser, nothing to maintain
Intercept response OR request, not both
Intercept request + response in the same script
No fallback if the server is unreachable
Fallback mode fires the mock on timeout
QA needs a staging environment to test error flows
Reproduce any response, any error, any sequence — in any browser

Five tools, one file, no account. Mock generator with tree-based JSON editor, bulk JSON editor with schema view and field history, validator with line-level error highlighting, diff, and beautifier. Import and export configs. Share a full mock via URL. Works in Chrome, Edge, and any Chromium-based browser — for frontend devs and QA engineers alike.

Open JediMock in your browser
Free. No install. No account. For frontend devs and QA engineers.
Open app → ⭐ Star on GitHub