ruby-sdk/CHANGELOG.md

Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[Unreleased]

[1.3.0] - 2026-08-22

User-facing documentation now lives on the documentation site at https://ruby.sdk.modelcontextprotocol.io, and README.md keeps the quick start. Two entries under "Changed" reject traffic that earlier releases accepted and ship in a minor release under the exceptions described in VERSIONING.md.

Added

• Add a resources_list_handler for context-dependent resource lists (#509)
• Pass a handler-returned _meta through the subscribe result (#510)

Changed

• Bound OAuth response bodies in the client (#520)
• Reject duplicate in-flight JSON-RPC request ids (#521)
• Move the documentation from README.md to the documentation site (#523)

[1.2.0] - 2026-08-15

This release completes the SEP-2575 stateless lifecycle of the 2026-07-28 specification, together with the SEP-2322, SEP-2549, and SEP-2243 features that revision builds on. Several entries under "Changed" are incompatible with 1.1.0 and ship in a minor release under the spec-conformance and security exceptions described in VERSIONING.md.

Added

• Handle the SEP-2575 modern request envelope in the server core (#475)
• Serve both lifecycle eras over stdio with an era lock per SEP-2575 (#478)
• Serve the sessionless modern path over Streamable HTTP per SEP-2575 (#479)
• Finalize server/discover and add client modern lifecycle support per SEP-2575 (#480)
• Let handlers return multi round-trip input_required results per SEP-2322 (#481)
• Add MCP::Elicitation::EnumSchema builders per SEP-1330 (#482)
• Stamp the required resultType on modern results per SEP-2322 (#487)
• Enforce the modern lifecycle admission rules per SEP-2575 (#489)
• Stream modern request notifications and honor the envelope logLevel per SEP-2575 (#490)
• Expose the user-defined server_context in instrumentation data (#493)
• Serve the subscriptions/listen notification stream per SEP-2575 (#495)
• Add opt-in requestState sealing via MCP::Server::RequestStateSecurity (#496)
• Mirror x-mcp-header tool parameters into Mcp-Param-* headers per SEP-2243 (#498)
• Stamp the required cache hints on modern cacheable results per SEP-2549 (#499)
• Drive multi round-trip input_required results on the client per SEP-2322 (#500)
• Fulfill input_required results on the legacy wire per SEP-2322 (#501)

Changed

• Align modern envelope validation with the finalized specification (#491)
• Require the Mcp-Method header on the modern path (#492)
• Bound server-to-client requests with a timeout (#502)
• Refuse server-to-client requests in the modern lifecycle per SEP-2575 (#503)
• Bound the total wait across SSE reconnection attempts (#504)
• Bound automatic pagination in the MCP client (#505)
• Reject modern-removed methods before the connection era locks (#511)
• Stop negotiating modern protocol versions through the initialize handshake (#516)

Deprecated

• Warn on modern client connects that declare the Roots or Sampling capabilities deprecated per SEP-2577 (#406, #516)

Fixed

• Stop leaking exception messages to clients via JSON-RPC error data (#486)
• Return Invalid Params for unknown prompts and missing prompt arguments (#517)
• Restrict OAuth discovery to same-origin metadata URLs and refuse private-network destinations

[1.1.0] - 2026-08-01

Added

• Support 2026-07-28 as the Latest Protocol Version (#476)
• Expose server tool annotations on MCP::Client::Tool (#445)

Fixed

• Preserve explicit tool response content (#469)

[1.0.0] - 2026-07-24

First stable release. The public API is now stable: breaking changes ship only in major releases, apart from the narrow exceptions documented in VERSIONING.md.

Added

• Add ROADMAP.md outlining the path toward SEP-1730 (#465)
• Add VERSIONING.md documenting the versioning and breaking-change policy (#466)

[0.25.0] - 2026-07-18

Added

• Support SEP-990 Cross-App Access via ID-JAG and the jwt-bearer grant (#454)
• Support client-side sampling via MCP::Client#on_sampling (#458)

Fixed

• Reject notifications carrying an unknown or expired session (#455)
• Handle an initialize request sent without an ID (#456)
• Bound client-side message buffering in the HTTP transport (#459)
• Lowercase response header names in StreamableHTTPTransport (#460)

[0.24.0] - 2026-07-12

Added

• Support SSE reconnection per SEP-1699 in the HTTP client transport (#426)
• Validate the RFC 9207 iss authorization response parameter per SEP-2468 (#431)
• Support private_key_jwt client authentication for the client_credentials grant (#432)
• Recognize multi round-trip input_required results per SEP-2322 (#433)
• Add opt-in ttlMs / cacheScope cache hints to List and Read results per SEP-2549 (#436)
• Add server/discover and stateless lifecycle error codes per SEP-2575 (#438)
• Associate server-to-client requests with the originating client request per SEP-2260 (#440)
• Add server-side MCP Apps helpers per SEP-1865 (#441)
• Support client-side elicitation with SEP-1034 schema defaults (#443)
• Support class-based Resource and ResourceTemplate definitions (#447)

Changed

• Bind stored client credentials to the authorization server issuer per SEP-2352 (#439)

Fixed

• Handle non-object JSON-RPC messages without raising (#448)
• Perform SSE stream writes outside the session mutex (#449)
• Validate required params for initialize and resources/subscribe (#451)

[0.23.0] - 2026-07-07

Added

• Add a session-ownership hook to StreamableHTTPTransport

Changed

• Require calling MCP::Client#connect before sending requests on stdio transport (#427)

Deprecated

• Annotate Roots, Sampling, and Logging APIs as deprecated per SEP-2577 (#429)

Fixed

• Fix an incorrect result: null response to an id-bearing notification message (#435)
• Validate Host and Origin headers to prevent DNS rebinding per MCP 2025-11-25
• Bound stateful session retention to prevent an initialize-flood DoS
• Bound stdio frame reads with max_line_bytes
• Bound request body and frame reads to prevent memory-exhaustion DoS

[0.22.0] - 2026-06-27

Added

• Add audience role validation for MCP::Annotations per MCP specification (#422)
• Send SEP-2243 Mcp-Method and Mcp-Name headers per MCP specification (#423)
• Support client-side notifications/cancelled per MCP specification (#425)

Changed

• Conform Tool Schemas to JSON Schema 2020-12 per SEP-2106 (#417)

Fixed

• Fix a SyntaxError on Ruby 2.7.0 caused by arguments forwarding syntax (#419)

[0.21.0] - 2026-06-20

Added

• Support capability extensions per SEP-2133 (#405)
• Add range validation for MCP::Annotations#priority per MCP specification (#410)
• Isolate stateless requests in ephemeral sessions per SEP-2567 (#415)

Changed

• Set OIDC application_type on Dynamic Client Registration per SEP-837 (#408)
• Fall back to legacy 2025-03-26 OAuth discovery for servers without PRM (#414)

[0.20.0] - 2026-06-14

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)

[0.19.0] - 2026-06-13

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)

[0.18.0] - 2026-05-30

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)

[0.17.0] - 2026-05-19

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)

[0.16.0] - 2026-05-14

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)

[0.15.0] - 2026-05-05

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)

[0.14.0] - 2026-04-24

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)

[0.13.0] - 2026-04-16

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)

[0.12.0] - 2026-04-11

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)

[0.11.0] - 2026-04-06

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)

[0.10.0] - 2026-03-30

Added

• Session expiry controls for StreamableHTTPTransport via session_idle_timeout: option (#268)

Changed

• ServerSession for per-connection state (#275)

Removed

• Remove Server#notify_progress broadcast API (#276)
• Remove undocumented handler override methods (#270)

Fixed

• Reject POST requests without session ID in stateful mode (#274)

[0.9.2] - 2026-03-27

Fixed

• Use accessor method in server_context_with_meta instead of ivar (#273)
• Reject duplicate SSE connections with 409 to prevent stream hijacking

[0.9.1] - 2026-03-23

Added

• Allow Client#call_tool to accept a tool name (#266)

Fixed

• Return 404 for invalid session ID in handle_delete (#261)

[0.9.0] - 2026-03-20

Added

• MCP::Client::Stdio transport (#262)
• Progress notifications per MCP specification (#254)
• Automatic _meta parameter extraction support (#172)
• CORS and Accept wildcard support for browser-based MCP clients (#253)

Changed

• Use autoload to defer loading of unused subsystems (#255)
• Reduce release package size (#239)

Fixed

• Return 404 for invalid session ID in handle_regular_request (#257)
• Use mutex-protected session_exists? in handle_regular_request (#258)

[0.8.0] - 2026-03-03

Added

• Content::EmbeddedResource class for embedded resource content type (#244)
• Content::Audio class for audio content type (#243)
• $ref support in Tool::Schema for protocol version 2025-11-25 (#242)
• MCP conformance test suite (#248)

Fixed

• Handle Errno::ECONNRESET in SSE stream operations (#249)
• Fix default handler return values to comply with MCP spec (#247)
• Fix Prompt#validate_arguments! crash when arguments are nil (#246)
• Return 202 Accepted for SSE responses per MCP spec (#245)
• Fix Content::Image#to_h to return mimeType (camelCase) per MCP spec (#241)

[0.7.1] - 2026-02-21

Fixed

• Fix Resource::Contents#to_h to use correct property names per MCP spec (#235)
• Return JSON-RPC protocol errors for unknown tool calls (#231)
• Fix logging/setLevel to return empty hash per MCP specification (#230)

[0.7.0] - 2026-02-14

Added

• logging support (#103)
• Protocol version negotiation to server initialization (#223)
• Tool arguments to instrumentation data (#218)
• Client info to instrumentation callback (#221)
• resource_templates to MCP::Client (#225)

Changed

• Extract MCP::Annotations into a dedicated file (#224)

Fixed

• Resource::Embedded not setting @resource in initialize (#220)

[0.6.0] - 2026-01-16

Changed

• Update licensing to Apache 2.0 for new contributions (#213)

Fixed

• Omit icons from responses when empty or nil to reduce context window usage (#212)

[0.5.0] - 2026-01-11

Added

• Protocol specification version "2025-11-25" support (#184)
• icons parameter support (#205)
• websiteUrl parameter in serverInfo (#188)
• description parameter in serverInfo (#201)
• additionalProperties support for schema validation (#198)
• "Draft" protocol version to supported versions (#179)
• stateless mode for high availability (#101)
• Exception messages for tool call errors (#194)
• Elicitation skeleton (#178)
• prompts/list and prompts/get support to client (#163)
• Accept header validation for HTTP client transport (#207)
• Ruby 2.7 - Ruby 3.1 support (#206)

Changed

• Make tool names stricter (#204)

Fixed

• Symlink path comparison in schema validation (#193)
• Duplicate tool names across namespaces now raise an error (#199)
• Tool error handling to follow MCP spec (#165)
• XSS vulnerability in json_rpc_handler (#175)

[0.4.0] - 2025-10-15

Added

• Client resources support with resources/list and resources/read methods (#160)
• _meta field support for Tool schema (#124)
• _meta field support for Prompt
• title field support for prompt arguments
• call_tool_raw method to client for accessing full tool responses (#149)
• Structured content support in tool responses (#147)
• AGENTS.md development guidance documentation (#134)
• Dependabot configuration for automated dependency updates (#138)

Changed

• Set default content to empty array instead of nil (#150)
• Improved prompt spec compliance (#153)
• Allow output schema to be array of objects (#144)
• Return 202 response code for accepted JSON-RPC notifications (#114)
• Added validation to MCP::Configuration setters (#145)
• Updated metaschema URI format for cross-OS compatibility

Fixed

• Client tools functionality and test coverage (#166)
• Client resources test for empty responses (#162)
• Documentation typos and incorrect examples (#157, #146)
• Removed redundant transport requires (#154)
• Cleaned up unused block parameters and magic comments

[0.3.0] - 2025-09-14

Added

• Tool output schema support with comprehensive validation (#122)
• HTTP client transport layer for MCP clients (#28)
• Tool annotations validation for protocol compatibility (#122)
• Server instructions support (#87)
• Title support in server info (#119)
• Default values for tool annotation hints (#118)
• Notifications/initialized method implementation (#84)

Changed

• Make default protocol version the latest specification version (#83)
• Protocol version validation to ensure valid values (#80)
• Improved tool handling for tools with no arguments (#85, #86)
• Better error handling and response API (#109)

Fixed

• JSON-RPC notification format in Streamable HTTP transport (#91)
• Errors when title is not specified (#126)
• Tools with missing arguments handling (#86)
• Namespacing issues in README examples (#89)

[0.2.0] - 2025-07-15

Added

• Custom methods support via define_custom_method (#75)
• Streamable HTTP transport implementation (#33)
• Tool argument validation against schemas (#43)

Changed

• Server context is now optional for Tools and Prompts (#54)
• Improved capability handling and removed automatic capability determination (#61, #63)
• Refactored architecture in preparation for client support (#27)

Fixed

• Input schema validation for schemas without required fields (#73)
• Error handling when sending notifications (#70)

[0.1.0] - 2025-05-30

Initial release in collaboration with Shopify