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Sniffy is an open-source traffic capture and debugging proxy for Windows, macOS, and Linux. It supports HTTP/HTTPS, WebSocket, gRPC, and SSE. Use it when debugging an HTTP endpoint, replaying a failing request to reproduce a bug, or returning a mock response to test how your client handles it. You can also pause a request or response at a breakpoint, edit its contents, and let it continue. - Inspect traffic: view the full contents of requests and responses - Send requests: cURL import and export - Apply rules: rewrite, redirect, block, and mock - Set breakpoints: intercept and edit a request or response - WebSocket: view messages in both directions - gRPC / SSE: view streaming sessions - Write plugins: modify requests and responses live with JavaScript, with hot reload, URL allowlists, and logs - Export sessions: HAR and JSON