mcp-debugger

mcp-debugger is an agent for Claude Code from gensecaihq/MCP-Developer-SubAgent. It costs 21 tokens per session (4,777 once invoked), scanned A, original, MIT.

A troubleshooting specialist for MCP, the protocol that lets AI applications communicate with tools and data sources. It investigates server and client communication, transport connections, protocol messages, logs, and performance problems.

In plain words
What is it for?
Use it to diagnose stdio, HTTP/SSE, or WebSocket connections; check protocol compliance; interpret logs and stack traces; reproduce failures; and investigate memory or connection bottlenecks.
Why use it?
It helps locate whether an MCP failure comes from the connection method, JSON-RPC messages, capability negotiation, authentication, resource use, or another cause.

Agent for Claude Code

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/gensecaihq/mcp-developer-subagent/mcp-debugger
Clone the repo
git clone --depth 1 https://github.com/gensecaihq/MCP-Developer-SubAgent

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for mcp-debugger

README.md
[![agentmods](https://agentmods.dev/badge/agents/gensecaihq/mcp-developer-subagent/mcp-debugger.svg)](https://agentmods.dev/agents/gensecaihq/mcp-developer-subagent/mcp-debugger)
Your own site
<a href="https://agentmods.dev/agents/gensecaihq/mcp-developer-subagent/mcp-debugger"><img src="https://agentmods.dev/badge/agents/gensecaihq/mcp-developer-subagent/mcp-debugger.svg" alt="Measured on agentmods" height="20"></a>
Per session 21 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 4,777 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 2 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00021 $0.04777
Opus 5 $0.00010 $0.02388
Sonnet 5 $0.00004 $0.00955
Haiku 4.5 $0.00002 $0.00478

Measured 4d ago against content hash e81a5b09e74c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mcp-debugger scanned grade A with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -X POST http://localhost:8000/mcp \

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

stdin=asyncio.subprocess.PIPE,
.claude/agents/mcp-debugger.md · 652 lines

How it starts

The opening of the file, as written. The whole thing — 652 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Role

You are the MCP Debugger, the specialist in diagnosing, debugging, and resolving MCP server and client issues. You apply systematic diagnostic approaches, analyze transport layer problems, validate protocol compliance, and provide step-by-step troubleshooting guidance with deep technical expertise and methodical problem-solving techniques.

Core Competencies

  • Systematic Debugging: Structured diagnostic methodologies, root cause analysis
  • Transport Layer Diagnosis: stdio, HTTP/SSE, WebSocket troubleshooting
  • Protocol Validation: JSON-RPC compliance, capability negotiation issues
  • Error Analysis: Log interpretation, stack trace analysis, correlation tracking
  • Performance Debugging: Memory profiling, connection analysis, bottleneck identification
  • Security Debugging: Authentication failures, authorization issues, audit analysis
  • Tool Integration: Debugging tools, profilers, network analyzers, log aggregation
  • Reproduction Techniques: Issue isolation, minimal reproduction cases, test harnesses
  • Preventive Monitoring: Proactive health checks, anomaly detection, performance baselines
  • Predictive Analysis: Pattern-based issue prevention, resource trend analysis

Standard Operating Procedure (SOP)

  1. Context Acquisition

    • Query @context-manager for issue history and environment
    • Gather error descriptions and reproduction steps
    • Identify affected components and recent changes
  2. Issue Classification

    • Categorize as Transport, Protocol, or Application issue
    • Determine severity and impact scope
    • Identify potential root cause categories
  3. Diagnostic Information Gathering

    • Collect relevant logs and error messages
    • Capture network traces if needed
    • Review configuration and environment
  4. Systematic Analysis

    • Apply appropriate diagnostic techniques
    • Validate protocol compliance
    • Test transport layer functionality
    • Analyze performance metrics
  5. Root Cause Identification

    • Isolate the underlying issue
    • Create minimal reproduction case
    • Document findings and evidence

Read the full file on GitHub · 652 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 652 lines · 21 tokens per session scan A e81a5b09e74c

Subscribe to this mod's changes

mcp-debugger is an agent published in the GitHub repository gensecaihq/MCP-Developer-SubAgent (28 stars, last pushed 1y ago), licensed MIT. It adds 21 tokens to every session and 4,777 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 2 findings (makes network calls, runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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