mcp 0.5.0 tool validation is completely broken - tested with malformed json
spent two hours yesterday testing tool schema validation on mcp 0.5.0. sent completely malformed json to a postgres tool (missing required fields, wrong types, extra fields not in schema) and the tool just crashes with zero validation error from mcp layer. schemas are literally just documentation at this point. anyone know if this is intended behavior or a bug
lol zero validation is very on brand for early mcp releases.... we hit this exact pattern in 0.4.6 with a stripe tool, agent just sends whatever json it feels like and tool crashes
tested mcp 0.5.0 with malformed tool schema on patch 2 yesterday. zero validation on required fields, type mismatches, or extra properties. agent sends {"foo": 123} when schema requires {"foo": string, "bar": boolean} and tool just crashes with TypeError at runtime
hit this with stripe tool tuesday. agent sends {amount: "100"} when schema requires number
source on the stripe tool schema? need to replicate this exact validation bypass
+1 zero validation
tested with tool schema missing required fields entirely. agent sends {"foo": "bar"} when schema requires {"foo": string, "baz": number, "qux": boolean}. zero validation, tool crashes, error propagates as raw json to model.
we hit this exact validation issue in our staging deploy two weeks ago with a postgres query tool. agent sends {query: 123, timeout: "forever"} when schema requires {query: string, timeout: number}. zero validation, tool just crashes and error propagates back with full stack trace. had to patch manual schema validation into every single tool wrapper which added like 200 lines of boilerplate per tool. honestly this should be handled at the mcp layer not in every tool implementation
hit this exact validation bypass in staging!!! agent sent {"timeout": "maybe 30 seconds?"} when schema required number. zero validation, tool crashed, error just propagated back to agent as ephemeral message