Intercept and debug Claude Code API requests using mitmproxy. Inspect system prompts, tool definitions, token usage, and streaming responses. Triggers: cc-trace, mitmproxy, API interception, Claude Code debugging, traffic inspection.
Capture and analyze Claude Code's API traffic using mitmproxy.
# 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
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
}
# 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 | 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" |
# Dump all captured requests
mitmdump -r ~/claude-flows.mitm -n --set flow_detail=2
# Show last prompt sent
bash scripts/show-last-prompt.sh
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', []))}")
| 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 |
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