mcp-spy

Q: How do I install mcp-spy?

Run npx skills add https://github.com/johnlindquist/claude --skill mcp-spy in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/mcp-spy/ (personal) or .claude/skills/mcp-spy/ (project).

by johnlindquistAI & Agents

Debug MCP server communication. Use for troubleshooting MCP integrations, viewing traffic, and analyzing latency.

Installs: 41
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/johnlindquist/claude --skill mcp-spy

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads mcp-spy automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

MCP Spy - Debug MCP Communication

Debug Model Context Protocol server integrations.

Overview

MCP Spy helps debug:

Message traffic between Claude and MCP servers
Latency issues
Failed requests
Protocol compliance

Traffic Analysis

View Recent Traffic

# Check MCP logs
tail -f ~/.claude/debug/mcp-*.log

# Or specific server
tail -f ~/.claude/debug/mcp-cm.log

Filter by Type

# Tool calls only
grep "tool_use" ~/.claude/debug/mcp-*.log

# Errors only
grep -i "error\|failed" ~/.claude/debug/mcp-*.log

# Specific tool
grep "beads_add" ~/.claude/debug/mcp-*.log

Latency Analysis

Measure Response Times

# Time a specific tool
time claude --print "Run beads_ready" --dangerously-skip-permissions 2>&1 | head -1

Find Slow Calls

# Look for latency warnings in logs
grep -i "timeout\|slow\|latency" ~/.claude/debug/mcp-*.log

Failed Request Analysis

Find Failures

# All errors
grep -i "error" ~/.claude/debug/mcp-*.log

# Parse error responses
grep "\"error\":" ~/.claude/debug/mcp-*.log | jq '.'

Common Issues

Connection refused - Server not running
Timeout - Server too slow
Invalid JSON - Malformed request/response
Unknown tool - Tool not registered

MCP Server Debug

Check Server Status

# Test server connection
curl -X POST http://localhost:3000/mcp/list_tools \
  -H "Content-Type: application/json" \
  -d '{}'

Server Logs

# View server logs (if running as process)
tail -f logs/mcp-server.log

# Or in terminal running server
# Logs appear in stdout

Test Tool Directly

# Call tool directly
curl -X POST http://localhost:3000/mcp/call_tool \
  -H "Content-Type: application/json" \
  -d '{
    "name": "beads_ready",
    "args": {}
  }'

Protocol Debugging

Inspect Messages

# Pretty print JSON messages
grep "message" ~/.claude/debug/mcp-*.log | jq '.'

Validate Requests

# Check request format
gemini -m pro -o text -e "" "Validate this MCP request format:

$(grep "request" ~/.claude/debug/mcp-*.log | tail -1)

Check:
1. Required fields present
2. Types correct
3. Schema compliance"

Troubleshooting Guide

Server Won't Start

# Check if port in use
lsof -i :3000

# Check server process
ps aux | grep mcp

# Start with verbose
node server/index.ts --verbose

Tool Not Found

# List available tools
curl http://localhost:3000/mcp/list_tools | jq '.tools[].name'

# Check tool registration
grep "registerTool\|toolRegistry" server/*.ts

Slow Responses

# Profile tool execution
time curl -X POST http://localhost:3000/mcp/call_tool \
  -H "Content-Type: application/json" \
  -d '{"name": "slow_tool", "args": {}}'

# Check for blocking operations
grep -i "await\|sync" tools/slow_tool/index.ts

JSON Parse Errors

# Find malformed JSON
grep -B 5 "JSON\|parse" ~/.claude/debug/mcp-*.log | grep -i error

# Validate JSON
echo '{"test": ...}' | jq '.'

Monitoring

Watch Traffic Live

# Real-time log monitoring
tail -f ~/.claude/debug/mcp-*.log | grep --line-buffered "tool_use\|result"

Traffic Stats

# Count calls per tool
grep "tool_use" ~/.claude/debug/mcp-*.log | \
  grep -oP '"name":"[^"]*"' | \
  sort | uniq -c | sort -rn

Health Dashboard

#!/bin/bash
# mcp-health.sh

echo "=== MCP Server Health ==="

# Check server
if curl -s http://localhost:3000/health > /dev/null 2>&1; then
  echo "Server: UP"
else
  echo "Server: DOWN"
fi

# Recent errors
ERRORS=$(grep -c "error" ~/.claude/debug/mcp-*.log 2>/dev/null || echo 0)
echo "Recent errors: $ERRORS"

# Tool count
TOOLS=$(curl -s http://localhost:3000/mcp/list_tools 2>/dev/null | jq '.tools | length' || echo 0)
echo "Registered tools: $TOOLS"

Best Practices

Enable logging - Keep debug logs on during development
Check health first - Verify server running before debugging
Test isolation - Test tools directly before through Claude
Monitor latency - Watch for degradation
Log rotation - Don't let logs grow unbounded
Error alerts - Set up monitoring for failures

FAQ

What does the mcp-spy skill do?

Debug MCP server communication. Use for troubleshooting MCP integrations, viewing traffic, and analyzing latency.

How do I install mcp-spy?

Run npx skills add https://github.com/johnlindquist/claude --skill mcp-spy in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/mcp-spy/ (personal) or .claude/skills/mcp-spy/ (project).

Which AI agents can use mcp-spy?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is mcp-spy safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains mcp-spy?

It is published by johnlindquist in johnlindquist/claude. It has 41 recorded installs.

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mcp-spy

Install

Install

Describe the task

Review the result

SKILL.md

MCP Spy - Debug MCP Communication

Overview

Traffic Analysis

View Recent Traffic

Filter by Type

Latency Analysis

Measure Response Times

Find Slow Calls

Failed Request Analysis

Find Failures

Common Issues

MCP Server Debug

Check Server Status

Server Logs

Test Tool Directly

Protocol Debugging

Inspect Messages

Validate Requests

Troubleshooting Guide

Server Won't Start

Tool Not Found

Slow Responses

JSON Parse Errors

Monitoring

Watch Traffic Live

Traffic Stats

Health Dashboard

Best Practices

FAQ

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