CheckPost

A DevTools panel to observe, intercept, mock, modify, replay, and export HTTP traffic.

CheckPost is a Chrome DevTools panel for inspecting and controlling the HTTP traffic of the page you are debugging. Watch every fetch/XHR live, then intercept, mock, modify, delay, block, or replay any request to force the edge cases and failure paths that are hard to reproduce, all without touching your backend. Features: live traffic capture with filtering and search; request breakpoints (pause, edit, forward, block, or mock a request in flight); rule-based mocking and response/header modification; environment host-switching; failure-scenario presets; replay with side-by-side diff; copy as cURL; and HAR export. Everything runs locally in your browser. CheckPost has no servers, no analytics, and collects no data.