Mockingbird

Hold, edit, and mock HTTP traffic for one tab — from a side panel, with no backend.

Mockingbird is a focused network-debugging tool for developers and QA engineers. Arm any tab and Mockingbird lets you see its HTTP(S) traffic, pause a request mid-flight to edit it, or replace it entirely with a mock response — all from a side panel, with no backend, no account, and no setup. WHAT YOU CAN DO • Capture live traffic for one tab — method, URL, status, size, timing — and inspect headers, query params, and pretty-printed JSON bodies. • Mock any endpoint — match by URL (glob, regex, or substring) and return a synthetic status, headers, body, and latency. Cross-origin mocks work automatically (CORS handled for you). • Passthrough + rewrite — let a request hit the network, then override status, merge headers, or rewrite JSON fields with JSONPath. • Breakpoints — hold a request at the request and/or response stage and edit it live, then continue or abort. Add a delay to simulate slow servers. • Replay & compose — re-send any captured request, or build one from scratch, and view the response. • Diff two responses, export the session as HAR, and export/import rule sets as JSON. PRIVACY — Mockingbird has no server and collects nothing. Captured traffic stays in memory; rules/settings are stored locally. The extension makes no network requests of its own. HOW IT WORKS — Uses the Chrome DevTools Protocol (the "debugger" permission), so Chrome shows a "debugging this browser" banner while a tab is armed. One tab at a time by design. Not affiliated with or endorsed by Google.