CC-Trace: Claude Code API Interception Skill

CC-Trace: Claude Code API Interception

Capture and analyze Claude Code's API traffic using mitmproxy.

Quick Start

# Start mitmproxy filtering Claude API traffic
mitmweb --web-port 8081 --set flow_filter='~d api.anthropic.com' --save-stream-file ~/claude-flows.mitm

# In another terminal, launch Claude through the proxy
proxy_claude

Shell Function

Add to ~/.zshrc or ~/.bashrc:

proxy_claude() {
    export HTTP_PROXY=http://127.0.0.1:8080
    export HTTPS_PROXY=http://127.0.0.1:8080
    export NODE_EXTRA_CA_CERTS="$HOME/.mitmproxy/mitmproxy-ca-cert.pem"
    export NODE_TLS_REJECT_UNAUTHORIZED=0
    claude
}

Certificate Setup (macOS)

# Generate cert (start mitmproxy once, then quit)
mitmproxy --set flow_filter='~d api.anthropic.com'

# Trust cert in system keychain
sudo security add-trusted-cert -d -p ssl -p basic -k /Library/Keychains/System.keychain ~/.mitmproxy/mitmproxy-ca-cert.pem

Filter Syntax

| Filter | Description | |--------|-------------| | ~d api.anthropic.com | Only Anthropic API | | ~m POST | Only POST requests | | ~s "tool_use" | Responses containing tool_use | | ~b "system" | Body contains "system" | | Combine | ~d api.anthropic.com & ~m POST & ~b "tool_use" |

Programmatic Analysis

# Dump all captured requests
mitmdump -r ~/claude-flows.mitm -n --set flow_detail=2

# Show last prompt sent
bash scripts/show-last-prompt.sh

Python Addon Example

from mitmproxy import http
import json

def response(flow: http.HTTPFlow):
    if "api.anthropic.com" in flow.request.pretty_host:
        req = json.loads(flow.request.get_text())
        print(f"Model: {req.get('model')}, Messages: {len(req.get('messages', []))}, Tools: {len(req.get('tools', []))}")

Bundled Scripts

| Script | Purpose | |--------|---------| | scripts/verify-setup.sh | Check mitmproxy install, cert trust, shell config | | scripts/parse-streamed-response.ts | Parse Anthropic SSE format | | scripts/extract-slash-commands.py | Extract user messages from flows | | scripts/show-last-prompt.sh | Show most recent user prompt |

Troubleshooting

security find-certificate -c mitmproxy -a  # verify cert
lsof -i :8080                               # check port
curl -x http://127.0.0.1:8080 https://api.anthropic.com 2>&1 | head -5

Agent Skills: CC-Trace: Claude Code API Interception

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