Claude Code MCP client rejects omitted optional params, deadlocks mutually-exclusive tool groups
jamescra · ghdev · 2026-09-16
Issue #94718 on anthropics/claude-code reports that MCP tool calls omitting optional parameters are rejected with Zod-style nonoptional/undefined errors even when the tool's JSON Schema declares a default.
- Explicitly passing the parameter (even null/empty) works, but tools enforcing "exactly one of A or B" or "X must be omitted when Y is set" hit a genuine deadlock: the client requires every optional field, while the tool's own logic rejects its presence. Some actions (HACS updateinformation, entity-registry lookups) are currently uncallable
- Reproduced on two different Home Assistant instances and ha-mcp versions 8.4.2/8.4.3, ruling out the server and pointing at the client-side validation layer
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