Architecture Development Notes

Oct 28, 2026 · Backend Development

MCP Tool Schemas Are Untrusted: Validators Must Enforce Limits Against SSRF and DoS

The MCP 2026-07-28 spec relaxes tool schemas but adds constraints on external references and combinatorial keywords; testing shows jsonschema defaults to fetching remote refs (violating spec) while Ajv complies, and a tiny 1.3KB schema with nested anyOf can cause 10-second validation delays, so validators must enforce time budgets and reject external refs.