Undercover Agent

A drop-in OpenAI-compatible chat completions server that sits between a coding harness (GitHub Copilot, OpenCode, or anything that speaks the OpenAI API) and a real model — and logs everything that flows through it.

Point your harness's "OpenAI base URL" at Undercover Agent, and every request and response is recorded into clean, browsable, per-conversation logs.

What it's for

When you're building or debugging an agent, the most useful thing you can have is the exact traffic the harness sends to the model: the full message history, system prompts, declared tools, sampling params, and the responses. Undercover Agent captures all of it without requiring any changes to the harness beyond a base-URL swap.

Two modes

• Dumb mode (default) — never contacts a real model. It returns well-formed, intentionally boring canned responses (correct choices, finish_reason, a plausible faked usage block) so the harness keeps working while you inspect what it's sending.
• MITM mode — forwards each request to a real upstream LLM via the official OpenAI SDK, relays the answer back unchanged, and logs everything in between.

Both modes stream when the request asks for it (stream: true), passing SSE through transparently.

Sessions

The OpenAI chat API is stateless — every request resends the whole conversation and carries no session id. Undercover Agent reconstructs sessions by prefix matching: if a stored conversation is a prefix of an incoming request's messages, the request is treated as a continuation of that session (longest match wins); otherwise a new session is born.

Each session gets a timestamped id like 20260630T101345Z-a1b2c3d4, so logs sort chronologically and any session can be opened directly by its id.

Install & run

Requires Python 3.9+.

pip install undercover-agent

Or, from a checkout of this repository:

pip install -r requirements.txt

Dumb mode (default)

python -m undercover_agent

Then point your harness at http://localhost:8000/v1.

MITM mode

python -m undercover_agent --mode mitm \
  --base-url https://api.openai.com/v1 \
  --api-key sk-...

The harness's own Authorization header is logged but never forwarded — Undercover Agent authenticates upstream with the --api-key you pass here.

CLI flags

HTTP API

Undercover Agent implements the slice of the OpenAI REST API that harnesses actually use:

• POST /v1/chat/completions — the main endpoint (streaming and non-streaming).
• GET /v1/models — returns the advertised model id(s).
• GET /health — liveness check.

Viewing the logs

Logs are written as one JSON file per session under logs/<session-id>.json. That JSON is the machine-readable report. There's also a human-readable HTML view, available two ways:

Live, while the server runs

• GET / — index of all sessions, newest first (timestamp, mode, model, turn count, token usage).
• GET /sessions/<session-id> — the full conversation rendered like a normal chat UI.
• GET /sessions/<session-id>.json — the raw JSON log.

Static export

python -m undercover_agent report

Writes reports/index.html plus one reports/<session-id>.html per session. Open reports/index.html and click through, or open a session file directly.

How it's built

• Flask for the HTTP server (streaming via generator responses).
• openai — the official SDK, used to forward requests upstream in MITM mode.

Entrypoint is python -m undercover_agent.