Protocol transport/auth evolution
MCP specification batching JSON-RPC batch requests not supported invalid request 2025-06-18
Only multi-tool operations fail with a generic invalid-request response.
Agent Quick Fix
Repair against the current MCP contract, then keep the change narrow and source-backed.
Product: MCP
Current-contract area: Legacy client sends batch requests to a server that changed batch policy
Likely root cause: Only multi-tool operations fail with a generic invalid-request response.
Repair direction: Verifier checks current transport framing, session lifecycle, auth flow, and backwards compatibility where specified.Symptom
Only multi-tool operations fail with a generic invalid-request response.
Why This Happens
Local client/server code can each be valid for an earlier protocol revision; only the negotiated current spec defines transport, session, and authorization behavior.
Common Wrong Fixes
- Changing local code without checking the current external contract.
- Retrying the same install, build, or API call with no version/source change.
- Applying a broad unsafe bypass when a narrow compatibility fix is available.
Codex Search Keywords
These are the search terms observed in a neutral Codex validation run for this failure shape.
MCP specification batching JSON-RPC batch requests not supported invalid request 2025-06-18
site:modelcontextprotocol.io/specification JSON-RPC batching MCP
Model Context Protocol specification JSON-RPC batch requests
github modelcontextprotocol specification batching JSON-RPC
https://modelcontextprotocol.io/specification/2025-06-18/basic
https://modelcontextprotocol.io/specification/2025-06-18/changelog