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Documentation Index

Fetch the complete documentation index at: https://modelcontextprotocol.io/llms.txt Use this file to discover all available pages before exploring further.

Key Changes

This document lists changes made to the Model Context Protocol (MCP) specification since the previous revision, 2025-06-18.

Major changes

  1. Enhance authorization server discovery with support for OpenID Connect Discovery 1.0. (PR #797)
  2. Allow servers to expose icons as additional metadata for tools, resources, resource templates, and prompts (SEP-973).
  3. Enhance authorization flows with incremental scope consent via WWW-Authenticate (SEP-835)
  4. Provide guidance on tool names (SEP-986)
  5. Update ElicitResult and EnumSchema to use a more standards-based approach and support titled, untitled, single-select, and multi-select enums (SEP-1330).
  6. Added support for URL mode elicitation (SEP-1036)
  7. Add tool calling support to sampling via tools and toolChoice parameters (SEP-1577)
  8. Add support for OAuth Client ID Metadata Documents as a recommended client registration mechanism (SEP-991, PR #1296)
  9. Add experimental support for tasks to enable tracking durable requests with polling and deferred result retrieval (SEP-1686).

Minor changes

  1. Clarify that servers using stdio transport may use stderr for all types of logging, not just error messages (PR #670).
  2. Add optional description field to Implementation interface to align with MCP registry server.json format and provide human-readable context during initialization.
  3. Clarify that servers must respond with HTTP 403 Forbidden for invalid Origin headers in Streamable HTTP transport. (PR #1439)
  4. Updated the Security Best Practices guidance.
  5. Clarify that input validation errors should be returned as Tool Execution Errors rather than Protocol Errors to enable model self-correction (SEP-1303).
  6. Support polling SSE streams by allowing servers to disconnect at will (SEP-1699).
  7. Clarify SEP-1699: GET streams support polling, resumption always via GET regardless of stream origin, event IDs should encode stream identity, disconnection includes server-initiated closure (Issue #1847).
  8. Align OAuth 2.0 Protected Resource Metadata discovery with RFC 9728, making WWW-Authenticate header optional with fallback to .well-known endpoint (SEP-985).
  9. Add support for default values in all primitive types (string, number, enum) for elicitation schemas (SEP-1034).
  10. Establish JSON Schema 2020-12 as the default dialect for MCP schema definitions (SEP-1613).

Other schema changes

  1. Decouple request payloads from RPC method definitions into standalone parameter schemas. (SEP-1319, PR #1284)

Governance and process updates

  1. Formalize Model Context Protocol governance structure (SEP-932).
  2. Establish shared communication practices and guidelines for the MCP community (SEP-994).
  3. Formalize Working Groups and Interest Groups in MCP governance (SEP-1302).
  4. Establish SDK tiering system with clear requirements for feature support and maintenance commitments (SEP-1730).

Full changelog

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