Mockbird

Intercept and mock API requests in real-time without touching code

Mockbird is a lightweight Chrome extension for frontend developers who need to test edge cases — errors, slow networks, conditional responses, real-time streams — without spinning up a backend or modifying production code. ━━━ WHAT IT DOES ━━━ • Intercept fetch / XHR / WebSocket / SSE by URL pattern (glob, substring, regex) • Swap responses with custom JSON, status codes, latency, headers • Capture real requests and turn them into mocks with one click • Compare mock vs live API in real time (drift detection) — see exactly what changed • GraphQL operation matching, header pattern matching, request body matching • Transform mode: write a JS function that modifies the real response • Simulate errors (4xx / 5xx), timeouts, network failures • Per-mock and global enable/disable — kill switch always one click away • Dark mode, keyboard shortcuts, full keyboard navigation ━━━ WHY IT'S DIFFERENT ━━━ • No code changes. • No desktop app. • Lightweight. • Affordable. Free forever for the core feature set. • 100% local. Your mocks live in chrome.storage.local — nothing leaves your machine. ━━━ EXPORT / IMPORT ━━━ • Export your mocks as JSON to share with your team • Import HAR files from DevTools to convert real traffic into mocks • Export to MSW (Mock Service Worker) format if you want to migrate to in-code mocking later ━━━ PRIVACY ━━━ Mockbird runs 100% on your device. No analytics, no telemetry, no tracking, no remote calls. Your mocks, captured requests, and configuration never leave