Introduction

Updated Jun 28, 2026

This guide documents the public API surface and usage patterns for the Spycatcher harness. The harness records LLM API interactions for deterministic regression testing. In record mode, both non-streaming and streaming ("stream": true) Chat Completions requests are proxied upstream and persisted to cassette. Replay mode serves matching non-stream responses and matching recorded Chat Completions SSE streams, including OpenRouter comment frames. Verify is currently a CLI-only command for cassette and configuration checks.

Breaking changes: record-mode proxying changed raw header handling and redaction defaults before the 0.1.0 release. See MIGRATION-0.1.0.md before updating cassette assertions or proxy-path tests.