Chrome DevTools extension

Mock any API inside DevTools, without waiting on the backend.

Mokup captures live Fetch/XHR traffic, turns any request into an editable mock rule, or forwards matching calls straight to your local server — path, query, method, headers and body preserved.

Add to Chrome See how it works

Free plan · 3 mock rules · No account needed · Your data never leaves your machine

Mokup panel inside Chrome DevTools showing requests labelled Real, Mocked and Forwarded
Features

Everything you need to unblock the frontend

Built for the way frontend developers actually work: capture real traffic, shape the response you need, keep moving.

Capture live requests

A Live tab records Fetch/XHR traffic with method, URL, status, type, source and timing — filterable by method, type and real/mocked/forwarded origin.

One-click mock rules

Turn any captured request into a rule instantly. Edit body, status code, matcher, method and artificial delay, then start editing.

Forward to local

Route matching calls to http://localhost:3000 or any target and stream the real response back — perfect for testing a new backend against production UI.

Response editor with undo

A JSON-aware editor with Ctrl+Z / Ctrl+Shift+Z undo and redo. Experiment with payload shapes without fear.

Simulate slow networks

Add per-rule latency to reproduce timeouts, loading skeletons and race conditions your users actually hit.

Local by design

Rules, preferences and captured data stay in your browser. No analytics, no tracking, no Mokup server in the middle.

How it works

Three steps from blocked to shipping

Mokup Live tab capturing real API requests in Chrome DevTools
01

Open the Mokup panel

Press F12, open a page, and pick the Mokup tab. Interception is injected into the inspected tab only while the panel is open.

Editing a mocked JSON response inside the Mokup response editor
02

Capture & create a rule

Reload the page, find the request in Live, then hit create mock. Edit the response body and status to match the contract you need — no restart, no rebuild.

Mokup Mock tab listing mock rules with enable toggles
03

Toggle and iterate

Flip rules on and off, set a delay, and compare Real, Mocked and Forwarded responses side by side.

React Vue Angular Svelte Vanilla JS Any Fetch / XHR app
Workflow

Built for real frontend handoffs

Stop hardcoding fixtures in your source or waiting for an endpoint to land. Keep experiments in DevTools, where they belong.

Ship UI before the API exists

Design against realistic payloads instead of placeholders, then swap in the real endpoint when it lands.

Reproduce edge cases on demand

Force 500s, empty lists, slow responses and malformed JSON to check every branch of your error handling.

Test the new backend early

Forward production traffic to your local server with one rule — no config files, no proxy setup, no restarts.

Hand QA the happy path

Rules persist across sessions, so testers reproduce the exact same state you saw, without a bespoke build.

Pricing

Free to start. Pro when you need more.

No subscription. Pro is a one-time lifetime license validated through Polar.

Free

$0 forever

For side projects and quick experiments.

  • Up to 3 mock rules
  • Live capture & filters
  • Forward to local
  • Undo/redo response editor
Install free
Launch offer

Pro

$59 one-time · lifetime

For developers who live in DevTools every day.

  • Unlimited mock rules
  • Everything in Free
  • All future Pro updates
  • Priority support by email
Get Pro lifetime
Early access: use LAUNCH50 for 50% off — first 100 customers
FAQ

Questions, answered

Does Mokup send my data anywhere?
No. Captured requests, mock rules and preferences stay on your machine in Chrome's local storage. Mokup has no analytics and no backend. The only network call the extension makes on your behalf is the forward target you configure, plus Polar license validation if you activate Pro.
Do I need to change my application code?
No. Mokup intercepts Fetch and XHR from the DevTools panel, so your app keeps calling the same URLs. Nothing to import, no service worker to register.
Does it work with React, Vue, Angular and Svelte?
Yes. Widgets built on Fetch or XHR work regardless of framework. The demo apps in the repository cover React, Vue and Angular.
What is "Forward to local" exactly?
For a matching rule, Mokup sends the request to the http:// or https:// target you set — usually a local dev server — and streams the real response back to the page. Path, query string, method, headers and body are preserved.
Do mocks survive a page reload?
Yes. While global mocking is on, Mokup registers early injection so enabled rules apply to requests that fire before the panel loads. Turning mocking off stops all interception immediately.
Is it a full proxy?
Mokup is a DevTools-scoped interceptor, not a system proxy. It focuses on Fetch/XHR during development. Navigation requests and binary downloads are out of scope for now.

Stop waiting on the backend. Start mocking.

Install Mokup, open DevTools, and turn your first captured request into a mock rule in under a minute.

Add to Chrome View on GitHub

Not on the Chrome Web Store yet? Load the unpacked build from the repository in a few clicks.