Differential Network Capture

Headroom includes a containerized harness for comparing Claude Code traffic sent directly to Anthropic with traffic sent through a Headroom proxy. The harness uses mitmproxy in two isolated lanes, writes sanitized JSONL captures, and then generates Markdown/JSON reports with request route, header, body size, body hash, and JSON payload differences.

Run The Harness

cd docker/differential-network-capture
mkdir -p captures
export ANTHROPIC_API_KEY=...
export CLAUDE_PROMPT="Summarize this repository in one sentence."
docker compose up --build mitm-direct mitm-headroom-upstream headroom-proxy mitm-headroom-client
docker compose --profile run run --rm claude-direct
docker compose --profile run run --rm claude-headroom

The primary captures are written to:

• docker/differential-network-capture/captures/direct.jsonl
• docker/differential-network-capture/captures/headroom-client.jsonl

The Headroom lane also writes docker/differential-network-capture/captures/headroom-upstream.jsonl, which is the request Headroom forwards to Anthropic after proxy processing.

By default only api.anthropic.com is logged. Override CAPTURE_INCLUDE_HOSTS with a comma-separated list to include other hosts.

Generate A Report

headroom capture network-diff \
  --direct docker/differential-network-capture/captures/direct.jsonl \
  --headroom docker/differential-network-capture/captures/headroom-client.jsonl \
  --output docker/differential-network-capture/captures/report.md \
  --json-output docker/differential-network-capture/captures/report.json

The report redacts sensitive header values and sensitive query values before comparison. Request bodies are captured so structural payload differences can be identified; keep the generated captures/ directory out of commits because it may contain prompts, tool outputs, and repository context.

For Claude Code deferred-tool investigations, the paired exchange table includes top-level Anthropic tools counts and serialized tool bytes. A jump from tools=0->N in the Headroom client lane is evidence that Claude Code eagerly materialized tool schemas before the request reached Headroom.

Custom Claude Invocation

Set CLAUDE_COMMAND to run the exact command under test in both lanes:

CLAUDE_COMMAND='claude -p "read README.md and summarize the proxy setup"' \
  docker compose --profile run run --rm claude-direct
CLAUDE_COMMAND='claude -p "read README.md and summarize the proxy setup"' \
  docker compose --profile run run --rm claude-headroom

Use CLAUDE_DIRECT_ARGS and CLAUDE_HEADROOM_ARGS when each lane needs different flags.