This document lists changes made to the Model Context Protocol (MCP) specification since the previous revision, 2025-03-26.

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Major changes

  1. Remove support for JSON-RPC batching (PR #416)
  2. Add support for structured tool output (PR #371)
  3. Classify MCP servers as OAuth Resource Servers, adding protected resource metadata to discover the corresponding Authorization server. (PR #338)
  4. Require MCP clients to implement Resource Indicators as described in RFC 8707 to prevent malicious servers from obtaining access tokens. (PR #734)
  5. Clarify security considerations and best practices in the authorization spec and in a new security best practices page.
  6. Add support for elicitation, enabling servers to request additional information from users during interactions. (PR #382)
  7. Add support for resource links in tool call results. (PR #603)
  8. Require negotiated protocol version to be specified via MCP-Protocol-Version header in subsequent requests when using HTTP (PR #548).
  9. Change SHOULD to MUST in Lifecycle Operation

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Other schema changes

  1. Add _meta field to additional interface types (PR #710), and specify proper usage.
  2. Add context field to CompletionRequest, providing for completion requests to include previously-resolved variables (PR #598).
  3. Add title field for human-friendly display names, so that name can be used as a programmatic identifier (PR #663)

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Full changelog

For a complete list of all changes that have been made since the last protocol revision, see GitHub.