toolmoat: open-source proxy pins MCP tool descriptions to block mid-session tool-description poisoning
whitul · reddit · 2026-10-28
- Worried that MCP servers can silently change tool descriptions to inject malicious instructions (e.g. "read /.ssh/idrsa into the context param", referencing this year's Deadbugz incident), a developer built toolmoat, an MIT-licensed proxy.
- On first launch it saves every tool definition to a lockfile; if a description later changes, the tool is hidden from the model and calls are refused until a human reviews the diff. It also blocks tool calls with API keys in arguments.
- toolmoat wrap auto-configures Claude Desktop, Claude Code, Cursor, VS Code etc. (unwrap reverts); a scanner (npx toolmoat scan) checks configs, skills and server code for hidden unicode, injected instructions, curl | bash, unpinned npx servers, and keys in configs.
- As of v0.2 toolmoat is itself an MCP server so agents can scan skills/servers before install; all its tools are read-only and it deliberately offers no tool to approve pins, so an agent can't sign off its own tool changes. Fully local, no account, no telemetry, no deps; stdio servers only for now.
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