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, fake or override 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 any error status on demand, from a 404 to a 500 • Loading states — add an artificial delay to test spinners and race conditions • CORS testing — add Access-Control-Allow-Origin and related headers to a mock • 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 • A full network log per tab, with each request's status, timing, headers and body • 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 • The log shows which rule answered each request Response Control • Serve any body — JSON, plain text, HTML, XML or a binary file • Override the status code, and set or remove response headers • Add a delay of up to 30 seconds • One-click presets for common status codes and delays • Dynamic values — a fresh ID or timestamp on every response, or data echoed from the request itself Targeting • Match URLs by wildcard, exact match, substring or regex • Limit a rule to the HTTP methods you choose • Rule priority decides which rule wins when several match • Test a URL against your rules to see which one wins • Per-tab — interception only affects the tab you switch it on for Rule Management • Organize rules into named groups and toggle a whole group at once • Import and export rules as JSON to share with your team • Toggle interception with a keyboard shortcut (Alt+Shift+I) or the right-click menu • 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 while interception is on Chrome shows a "…started debugging this browser" banner. That's Chrome's notice, not ours, and it disappears once 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: • No network requests of its own. No analytics, no telemetry, no error reporting, no phone-home of any kind. The only thing it ever downloads is a file you ask for, when you load a binary mock body from a URL • 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.