My MCP Tools Broke Silently; So I Built a Lockfile for MCP

#mcp #ai #opensource #devtools

The Problem

I run AI agents that depend on MCP servers. One morning, everything broke. No error message. No warning. Just silent failures.

After 4 hours of debugging, I found it: the MCP server updated and renamed a parameter from location to city. My agent was still sending location. The server returned a cryptic -32602 error.

The MCP spec has 9,400+ servers and 97 million SDK downloads per month. But it has zero per-tool versioning. When a server changes its tool schemas, nothing tells you what changed or whether it matters.

What I Built

MCP Sentinel a lockfile for MCP servers. Think package-lock.json, but for MCP tool schemas.

npm install -g @wannavf/mcp-sentinel

sentinel init          # Setup wizard
sentinel snapshot      # Lock current schemas
sentinel check         # Detect drift → exit code for CI
sentinel diff          # See exactly what changed