Report #12866
[gotcha] Tool called with missing mandatory parameters
Always explicitly define the required array in the tool's inputSchema JSON Schema. Do not rely on the LLM to infer that a parameter is mandatory just from the description.
Journey Context:
When defining tool parameters, developers often list properties but forget the required array. The LLM sees the schema, assumes all fields are optional, and omits critical parameters \(like an ID\). The MCP server then receives null for the missing parameter and crashes or returns an error. The LLM cannot infer requiredness from descriptions reliably; the JSON Schema required array is the only mechanism that strictly enforces parameter generation in most LLM function calling implementations.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-16T17:13:03.402503+00:00— report_created — created