mcp_client 2.0.0

Dart implementation of Model Context Protocol (MCP) client. Supports protocol revisions 2024-11-05 / 2025-03-26 / 2025-06-18 / 2025-11-25 with per-version capability negotiation, OAuth 2.1, and stdio [...]

2.0.0 - 2026-04-30 - MCP spec compliance + 2025-11-25 alignment

Big-Bang spec normalization. Supports protocol revisions 2024-11-05, 2025-03-26, 2025-06-18, and 2025-11-25 with per-version capability gating. Pairs with mcp_server 2.0.

Breaking

• Sampling direction fixed. client.createMessage(...) (which sent a request to the server) is removed. Sampling is server-initiated per spec — register a handler with client.onSamplingRequest((req) async { ... }) so the host LLM fulfils it.
• Roots direction fixed. client.listRoots() (which sent a request to the server) is removed. The server requests roots from the client; configure them locally with client.addRoot(...) / client.removeRoot(...) and read via client.roots. Override the default response handler with client.onListRoots(...). roots/add and roots/remove JSON-RPC methods (non-spec) are deleted.
• Cancellation is now a notification. client.cancelOperation(opId) (which sent a cancel request) is removed; use client.notifyCancelled(requestId, reason: ...) which emits the spec notifications/cancelled notification.
• Logging method name corrected. setLoggingLevel now sends logging/setLevel (camelCase) per spec — was logging/set_level.
• client.healthCheck() removed — health/check is non-spec; expose health via your transport (e.g. an HTTP /health endpoint).
• onSamplingResponse listener removed — the non-spec sampling/response notification path is gone, replaced by the standard request/response shape.

Added

• client.onSamplingRequest(handler) — register a host LLM completion handler.
• client.onElicitationRequest(handler) — register a user-input handler (spec 2025-06-18 elicitation/create).
• client.onListRoots(handler) — override the default roots/list response.
• client.notifyCancelled(requestId, {reason}) and client.notifyProgress(token, progress, {total, message}) — spec notifications.
• ClientCapabilities.elicitation flag.
• McpProtocol.v2025_06_18 and McpProtocol.v2025_11_25 constants. defaultVersion advances to v2025_11_25.
• Per-version capability gates: McpProtocol.supportsBatching / supportsElicitation / requiresProtocolHeader.
• Schema: Tool.title / Tool.outputSchema / Tool.icons / Tool.meta. CallToolResult.structuredContent. AudioContent. ResourceLinkContent.
• Incoming-request infrastructure routes server-initiated requests to registered handlers and returns a JSON-RPC response with the matching id.

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1.1.1 - 2026-04-28

Changed

• README cleanup — removed "MCP Family" section, installation block, dev.to articles, and donation links.

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1.1.0

• New Features
  • Deferred Tool Loading support (Progressive Tool Disclosure)
    • ToolMetadata - Lightweight tool representation (name + description only)
    • ToolRegistry - Cache layer for tool definitions with metadata extraction
    • ClientToolMetadataExtension - Extension for easy metadata access
    • Reduces token usage by 60-80% when sending tool definitions to LLMs
    • Zero breaking changes - fully backward compatible, opt-in only

1.0.2

• Bug Fixes
  • Added terminateOnClose parameter to StreamableHTTP transport configuration
    • Allows controlling whether DELETE request is sent on disconnect
    • Default value is true to maintain backward compatibility
    • Set to false to allow reconnection after disconnect without server session termination
  • Enhanced session validation and localStorage management
    • Server-side session validation through hasSession() check
    • Automatic localStorage cleanup when session ID changes (server restart detection)
    • Proper handling of invalid/expired session IDs
    • Improved reconnection logic for StreamableHTTP transport

1.0.1

• Bug Fixes
  • Fixed SSE endpoint parsing issue where endpoint data was incorrectly processed as null
  • Added support for SSE events without explicit event type field
  • Improved compatibility with various SSE server implementations
  • Fixed web platform SSE implementation to match native platform behavior

1.0.0

• Breaking Changes and Major Update to 2025-03-26 Protocol

  • Updated to MCP protocol version 2025-03-26 (from 2024-11-05)
  • Complete refactoring for modern Dart 3.8+ patterns
  • Added @immutable annotations throughout models
  • Introduced sealed classes and pattern matching
  • Enhanced type safety with Result<T, E> pattern
  • Backward API compatibility maintained

• New Features

  • Protocol version negotiation support
  • Enhanced Content model with annotations
  • Tool cancellation and progress tracking
  • Improved resource templates
  • Better error handling with typed results
  • Protocol constants centralized in McpProtocol class

• Technical Improvements

  • All models now use const constructors
  • Factory constructors for JSON deserialization
  • Centralized protocol configuration
  • Better numeric type handling in JSON
  • Cleaner API surface with protocol exports

0.1.8

• Added
  • Client event monitoring system using Dart's Stream API
    • onConnect stream for server connection events
    • onDisconnect stream for server disconnection events
    • onError stream for error events
  • New models to support event monitoring
    • ServerInfo class for connection details
    • DisconnectReason enum for disconnect causes
  • Client lifecycle management improvements
    • Added dispose() method for proper resource cleanup
    • Enhanced error propagation through dedicated stream
    • Better connection state tracking and reporting

0.1.7

0.1.6

0.1.5

• Bug Fixed

0.1.4

• Bug Fixes

0.1.3

• Fixed
  • SSE Transport Connection Issues: Fixed critical issue with Server-Sent Events (SSE) connection where the client could not properly process JSON-RPC responses from the server.
    • Improved event stream processing to correctly parse JSON-RPC messages
    • Fixed handling of the endpoint event to establish the message channel
    • Enhanced buffer management for fragmented SSE event data
  • JSON-RPC Message Flow: Corrected the bidirectional communication flow between client and server:
    • Client requests via HTTP POST to message endpoint now properly receive responses
    • Fixed timeout issues by correctly handling asynchronous SSE responses
• Improved
  • Error Handling: Enhanced error reporting and recovery for connection issues
  • Logging: Added more detailed diagnostic logging for easier troubleshooting
  • Stability: More robust message endpoint URL construction and session handling
• Technical Notes
  • Updated SseClientTransport implementation to maintain persistent connections
  • Fixed JSON response type handling for resource templates
  • Improved session management and reconnection logic

0.1.2

• New Features
  • Protocol Update: Full support for all features of the 2024-11-05 protocol specification
  • Progress Tracking: Added onProgress method to receive notifications about progress of long-running operations
  • Operation Cancellation: Added cancelOperation method to cancel running operations
  • Server Health Check: Added healthCheck method to check server's health status
  • Resource Template Enhancement: Added getResourceWithTemplate method to access resources using URI templates
  • Tool Execution with Progress Tracking: Added callToolWithTracking method that returns operation IDs
  • Enhanced Resource Update Notifications: Added onResourceContentUpdated method that includes content information
  • Sampling Response Handling: Added onSamplingResponse method to process sampling results
• New Model Classes
  • ServerHealth: Class to hold server health status information
  • PendingOperation: Class for managing ongoing operations
  • ProgressUpdate: Class for operation progress updates
  • CachedResource: Class for resource caching
  • ToolCallTracking: Class to return tool call results and operation IDs together
• Technical Improvements
  • Enhanced protocol version validation
  • Improved error handling and exception messages
  • Added options to colorize logs and include timestamps for easier debugging

0.1.1

• Bug fixes

0.1.0

• Initial release
• Created Model Context Protocol (MCP) client implementation for Dart
• Features:
  • Connect to MCP servers with standardized protocol support
  • Access data through Resources
  • Execute functionality through Tools
  • Utilize interaction patterns through Prompts
  • Support for Roots management
  • Support for Sampling (LLM text generation)
    • Multiple transport layers:
    • Standard I/O for local process communication
  • Server-Sent Events (SSE) for HTTP-based communication
  • Platform support: Android, iOS, web, Linux, Windows, macOS