v0.20.0

Added

• Support W3C Trace Context Propagation via _meta per SEP-414 (#397)
• Support OAuth client_credentials grant in OAuth client (#399)
• Add annotations field to MCP::Resource and MCP::ResourceTemplate per MCP specification (#403)

Changed

• Re-run OAuth flow on 403 insufficient_scope (step-up) (#368)
• Speed up Tool::Schema validation by 5x to 100x (#369)
• Use JSON-RPC error envelope for StreamableHTTPTransport errors (#371)
• Pin RFC 8414 default well-known suffix per SEP-2351 (#395)
• Default missing MCP-Protocol-Version to 2025-03-26 in StreamableHTTPTransport (#392)

Fixed

• Preserve the request ID in invalid request error responses (#400)
• Standardize Resource Not Found errors on -32602 with URI data per SEP-2164 (#402)

v0.19.0

Added

• Support Client ID Metadata Documents in OAuth client (#361)
• Request offline_access scope when supported (#365)
• Add size field to MCP::Resource per MCP specification (#393)

v0.18.0

Added

• Support server-to-client ping per MCP specification (#358)

Changed

• Warn on implicit stdio initialization (#338)
• Cache Tool::Schema validation to avoid re-validating identical schemas (#363)

Fixed

• Fix case-sensitive Accept header comparison (#359)

v0.17.0

Added

• Add OAuth 2.1 client support for MCP authorization flow (#353)

Fixed

• Validate MCP-Protocol-Version header in StreamableHTTPTransport (#347)
• Reject duplicate initialize requests (#350)
• Reject non-Hash JSON-RPC bodies in StreamableHTTPTransport (#354)

v0.16.0

Added

• Add opt-in tool output validation (#344)

Changed

• Advertise JSON Schema 2020-12 dialect on emitted tool schemas (#342)

Fixed

• Preserve client tool output schemas (#343)
• Fix missing output_schema argument in define_tool API (#301)

v0.15.0

Added

• Support notifications/cancelled per MCP specification (#332)
• Add client-level connect for initialize handshake (#327)
• Add client-level connect handshake to stdio transport (#336)

Changed

• Return tool argument validation failures as tool execution errors (#333)

Removed

• Remove obsolete MCP::Transports module (#331)

v0.14.0

Added

• Support pagination per MCP specification (#320)
• Support resource subscriptions per MCP specification (#313)
• Add roots/list and notifications/roots/list_changed support (#315)
• Support JSON response mode for StreamableHTTPTransport (#328)
• Add HTTP client close for explicit session termination (#326)
• Track Mcp-Session-Id and protocol version in HTTP client (#325)
• Support ping client API per MCP specification (#324)

Fixed

• Handle 202 Accepted response in HTTP client (#323)

Changed

• Parse SSE responses in HTTP client via event_stream_parser (#322)

v0.13.0

Added

• Make StreamableHTTPTransport a Rack application (#263)
• Support elicitation/create per MCP specification (#312)
• Add around_request hook for request instrumentation (#309)
• Add _meta field to resource, content, and result classes (#310)

Removed

• Remove Server#create_sampling_message direct call (#311)

v0.12.0

Added

• Support customizing the Faraday client in MCP::Client::HTTP (#306)

Changed

• Auto-set server.transport in Transport#initialize (#305)

Fixed

• Validate Content-Type on POST requests (#304)

v0.11.0

Added

• Support sampling/createMessage per MCP specification (#282)
• Support completion/complete per MCP specification (#289)

Fixed

• Support POST response SSE streams for server-to-client messages (#294)
• Return protocol errors for invalid arguments and server errors (#285)
• Fix client methods silently swallowing JSON-RPC error responses (#281)
• Close streams outside mutex in session cleanup (#291)