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