API Interceptor - Mock API Responses & Intercept HTTP Requests

Mock API responses in one click. Capture a real request, turn it into a mock. No account, no cloud — nothing leaves your machine.

Mock any API response in your browser — without touching your backend. API Interceptor is a free tool for frontend developers who need to test against an API that isn't ready, isn't cooperating, or isn't theirs. Capture the real requests your page makes, turn any one of them into a mock in a click, and reload. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ THE FAST WAY IN ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1. Click the extension icon and turn on "Intercept this tab" 2. Reload the page — every request it makes is captured 3. Hit "+ Rule" on the request you want to fake. The mock is already prefilled with the response your server actually returned 4. Edit the body or status code, save, reload 5. Toggle interception off — real API behavior returns instantly No hand-writing mock payloads. You edit real data instead of inventing it. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ WHAT DEVELOPERS USE IT FOR ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ • API Mocking — build the frontend before the backend exists • Error Simulation — return 401, 403, 404, 429, 500 or any status on demand • Loading States — add an artificial delay to test spinners and race conditions • CORS Testing — inject Access-Control-Allow-Origin and friends • Demo Mode — lock in consistent data for client demos • Third-Party APIs — mock endpoints you don't control and can't change ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ KEY FEATURES ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Record and Mock • Full network log per tab — URL, method, status, duration, headers, bodies • One click turns any captured request into a rule, prefilled with the real response • Bulk mock — select several requests and create every rule at once • Paste a cURL command or a URL to build a rule instantly Response Control • Serve any body: JSON, text, HTML, XML, or binary • Override the status code — 200, 401, 403, 404, 429, 500, anything • Add, override, or remove response headers • Add a delay from 0 to 30000 ms Targeting • Match by wildcard, exact URL, contains, or regex • Filter by method — GET, POST, PUT, PATCH, DELETE • Rule priority decides which rule wins when several match • Per-tab — interception only affects the tab you switch it on for Rule Management • Organize rules into named groups, toggle a whole group at once • Import and export as JSON to share with your team • Dark mode ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ HOW IT WORKS — AND WHAT IT DOESN'T DO ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ When a request matches one of your rules, the extension blocks it and answers with your mock. Your real server is never contacted for that request. It is a mocking tool, not a proxy. It does not fetch the genuine response and edit it in flight. To see the real response, disable the rule or switch interception off. It uses Chrome's debugger API, so Chrome shows a "being debugged" banner on the tab while interception is on. That's Chrome's notice, not ours, and it disappears the moment you switch interception off. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ PRIVACY & SECURITY ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ An API interceptor sees everything you send — auth tokens, session cookies, customer data. This one is built so that never matters: • Zero network requests of its own. No analytics, no telemetry, no error reporting, no phone-home of any kind • No account. There's no sign-up because there's no server to sign up to • Rules and captured traffic live in local browser storage and never leave your machine • The debugger only attaches to tabs you explicitly turn it on for Free. No paid tier, no feature gates, no usage limits.