01
Describe the request
Pick a method and a URL pattern — contains, path params, exact or regex — then narrow it with query, header, body or GraphQL conditions.
Chrome extension for API mocking
Mock APIs directly in Chrome DevTools
Mockrew is a Chrome extension that intercepts XHR & Fetch, returns mock responses, simulates errors and delays, and rewrites requests & responses — no proxy required, no backend changes. Rules stay active on every page whether DevTools is open or not.
Mockrew InterceptingSearch rules (name / URL)Demo project 6 / 6AllMockRewriteHeadersRedirect+ New rule
GET/api/usersMock200MockJS
POST/api/ordersMock201Template
GET/api/orders/:idMock500Static
PATCH/api/profileMock200JS
GET/api/feature-flagsMock200Template
DELETE/api/cart/:idMock204Static
Request log4 Hits onlyFilter by URL
09:41:02GET/api/users200318ms
09:40:48GET/api/orders/:id50012ms
09:40:33POST/api/orders201120ms
09:40:27GET/api/users200321ms
- Interception runs locally in your browser
- No proxy, no certificate to trust
- Works without an account
From a real request to a mocked response
Three steps, no build step and no configuration file.
02
Choose the response
Return a mock with your own status, delay and JSON body, let a Faker template generate data, walk through a sequence, or run a JS hook.
03
Watch it happen
The request log shows what matched and which step answered. Turn any real request into a rule with one click.
Built for real debugging workflows
From simple static responses to state machines and dynamic scripts — covering most day-to-day integration cases.
Rules organized by project
Global, project and per-rule toggles with drag-and-drop ordering; rules match in order and the first enabled hit wins.
Four match modes + conditional hits
Contains, path parameters, exact and regex URL matching, plus declarative branching by query, header, JSON body or GraphQL operation.
Sequenced responses (state machine)
Return different responses on successive hits, with stop-at-last or loop — perfect for polling and state transitions.
Faker templates and JS hooks
Generate realistic fake data from templates, or write a JS hook that reads the request context to build the response.
Network request layer: rewrite and redirect
Rewrite real request / response headers or redirect URLs to another origin via declarativeNetRequest.
Request log with one-click rule creation
Inspect hits and sequence steps, then turn any logged request into a rule — the whole debugging path stays visible.
A look at the UI
The DevTools panel is your rule manager and request log, in light or dark theme.
Rule list: organized by project, conditions and actions at a glance
How it differs from a local proxy
Both approaches can fake an API. The difference is where the request is intercepted and what you have to install to get there.
| Capability | Mockrew | Local proxy tooling |
|---|---|---|
| Certificate to install and trust | None | A root CA on the machine or device |
| Where requests are intercepted | Inside the page (fetch / XHR) and in the browser's network request layer | Outside the browser, after the traffic leaves it |
| Changes needed in the app | None | None, but the proxy must be running |
| Coverage | fetch / XHR in the page; all request types for headers and redirects | All HTTP traffic from the machine, including other apps |
Your traffic never leaves the browser
Mocking means handling requests that may carry cookies and tokens. Mockrew is designed so they never travel any further.
Local-only storage
Rules, responses and scripts live in the extension’s local storage. Request URLs, headers and bodies are never uploaded.
No telemetry
No analytics, no crash reporting, no usage counters. The extension contacts our server only to activate and validate a Pro licence — never about your API traffic.
Works offline
Interception and mocking do not need a connection, and the Free plan needs no account at all.
Free to start, Pro when you need it
The core toolkit costs nothing. Pro lifts the limits and unlocks dynamic responses.
Free
20 rules, 5 of them active at a time, plus two projects — all the matching, mocking and network request layer actions.
Get started freePro
Billing opens soonUnlimited rules and projects, sequenced responses, JS Hooks and request / response hooks.
Compare plansFAQ
No. The interception script is injected when the page loads and stays active. The DevTools panel is just the rule manager and request log.
The page layer covers fetch and XMLHttpRequest. Network request layer actions cover every request type, including subresources and document navigations.
Rules live in your browser's local extension storage and are never uploaded. Pro will add optional cloud sync.
The core toolkit is free for personal development. Pro is $3.50/month or $35/year and unlocks unlimited rules and projects, sequenced responses, dynamic JavaScript responses and hooks — with a 7-day free trial, no card required. Billing opens soon; the trial is available today.
Chrome 116 or newer. That is the first version with the declarativeNetRequest dynamic-rule and offscreen-document capabilities Mockrew relies on.
Rules can point at any API, so the injected script has to be able to run on any page you debug. It only reads requests your page makes, and only answers the ones a rule matches. It never asks for the debugger permission.
Sign in, open your account page (/account) and click Cancel subscription under Billing — that opens the customer portal where you cancel. You can also use the portal link in your payment receipt, or email support. Cancellation stops future charges and Pro keeps working until the end of the period you already paid for.
All payments are generally non-refundable. We do refund where the law requires it, and where we confirm a billing error, an unauthorised charge or a failure of the paid service on our side; an unused subscription may also be refunded at our discretion. Try the free 7-day trial before you buy — the full policy is on the refund policy page.
Yes — Export writes every project to one JSON file, and Import reads it back. You can also import OpenAPI / Swagger, a Postman collection or a cURL command to generate a rule set from an API document.