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.
npx agentmods add rules/giantswarm/mcp-debug/mcp-debugginggit clone --depth 1 https://github.com/giantswarm/mcp-debugWhat 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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00000 | $0.01136 |
| Opus 5 | $0.00000 | $0.00568 |
| Sonnet 5 | $0.00000 | $0.00227 |
| Haiku 4.5 | $0.00000 | $0.00114 |
Grade A, and why
mcp-debugging scanned grade A with 0 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 yesterday.
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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 180 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Debugging MCP Servers via MCP-Debug Agent
The mcp-debug agent provides essential tools to test and explore MCP (Model Context Protocol) servers. This guide focuses on using the agent to debug MCP server behavior and functionality.
Core Agent Modes
The agent operates in three distinct modes:
1. Normal Mode (Default)
Connects to an MCP server, lists available tools/resources/prompts, and waits for notifications:
mcp-debug --endpoint http://localhost:8090/sse
2. REPL Mode
Interactive mode for exploring and executing MCP capabilities:
mcp-debug --repl
In REPL mode, you can:
- List available tools, resources, and prompts
- Get detailed information about specific items
- Execute tools interactively with JSON arguments
- View resources and retrieve their contents
- Execute prompts with arguments
- Toggle notification display
3. MCP Server Mode
Run the agent as an MCP server exposing debugging tools via stdio:
mcp-debug --mcp-server
This mode is designed for integration with AI assistants like Claude or Cursor. Configure it in your AI assistant's MCP settings.
REPL Commands
Listing Commands
list tools # List all available tools
list resources # List all available resources
list prompts # List all available prompts
Describe Commands
describe tool <name> # Show detailed information about a tool
describe resource <uri> # Show detailed information about a resource
describe prompt <name> # Show detailed information about a prompt
Execution Commands
call <tool> {json} # Execute a tool with JSON arguments
get <resource-uri> # Retrieve a resource
prompt <name> {json} # Get a prompt with JSON arguments
Control Commands
notifications <on|off> # Enable/disable notification display
help, ? # Show help message
exit, quit # Exit the REPL
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.
- yesterday First seen · 180 lines · 0 tokens per session scan A 67365c333b2f
mcp-debugging is a cursor rule published in the GitHub repository giantswarm/mcp-debug (37 stars, last pushed 5d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 1,136 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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