0.3.0-wip

  • Added error checking to required fields of all Request subclasses so that they will throw helpful errors when accessed and not set.
  • Added enum support to Schema.
  • Add more detail to type validation errors.
  • Remove some duplicate validation errors, errors are only reported for the leaf nodes and not all the way up the tree.
    • Deprecated a few validation error types as a part of this, including propertyNamesInvalid, propertyValueInvalid, itemInvalid and prefixItemInvalid.
  • Added a custom validation error type.
  • Breaking: Auto-validate schemas for all tools by default. This can be disabled by passing validateArguments: false to registerTool.
  • Updates to the latest MCP spec, 2025-06-08
    • Adds support for Elicitations to allow the server to ask the user questions.
    • Adds ResourceLink as a tool return content type.
    • Adds support for structured tool output.
  • Breaking: Change MCPClient.connectStdioServer signature to accept stdin and stdout streams instead of starting processes itself. This enables custom process spawning (such as using package:process), and also enables the client to run in browser environments.

0.2.2

  • Refactor ClientImplementation and ServerImplementation to the shared Implementation type to match the spec. The old names are deprecated but will still work until the next breaking release.
  • Add clientInfo field to MCPServer, assigned during initialization.
  • Move the done future from the ServerConnection into MCPBase so it is available to the MPCServer class as well.

0.2.1

  • Fix the protocolLogSink support when using MCPClient.connectStdioServer.
  • Update workflow example to show thinking spinner and input and output token usage.
  • Update file system example to support relative paths.
  • Fix a bug in notification handling where leaving off the parameters caused a type exception.
  • Added --help, --log, and --model flags to the workflow example.
  • Fixed a bug where the examples would only connect to a server with the latest protocol version.
  • Handle failed calls to listRoots in the RootsTrackingSupport mixin more gracefully. Previously this would leave the roots future hanging indefinitely, but now it will log an error and set the roots to empty.
  • Added validation for Schema extension.
  • Fixed an issue where getting the type of a Schema with a null type would throw.

0.2.0

  • Support protocol version 2025-03-26.
    • Adds support for AudioContent.
    • Adds support for ToolAnnotations.
    • Adds support for ProgressNotification messages.
  • Save the ServerCapabilities object on the ServerConnection class to make it easier to check the capabilities of the server.
  • Add default version negotiation logic.
    • Save the negotiated ProtocolVersion in a protocolVersion field for both MCPServer and the ServerConnection classes.
    • Automatically disconnect from servers if version negotiation fails.
  • Added support for adding and listing ResourceTemplates.
    • Handlers have to handle their own matching of templates.
  • Added a RootsTrackingSupport server mixin which can be used to keep an updated list of the roots set by the client.
  • Added default throttling with a 500ms delay for ResourceListChangedNotifications and ResourceUpdatedNotifications. The delay can be modified by overriding ResourcesSupport.resourceUpdateThrottleDelay.
  • Add Sink<String> protocolLogSink parameters to server constructor and client connection methods, which can be used to capture protocol messages for debugging purposes.
  • Only send notifications if the peer is still connected. Fixes issues where notifications are delayed due to throttling and the client has since closed.
  • Breaking: Fixed paginated result subtypes to use nextCursor instead of cursor as the key for the next cursor.
  • Breaking: Change the ProgressNotification.progress and ProgressNotification.total types to num instead of int to align with the spec.
  • Breaking: Change the protocolVersion string to a ProtocolVersion enum, which has all supported versions and whether or not they are supported.
  • Breaking: Change InitializeRequest and InitializeResult to take a ProtocolVersion instead of a string.
  • Breaking: Change the InitializeResult's instructions to String? to reflect that not all servers return instructions.
  • Change the MCPServer.fromStreamChannel constructor to make the instructions parameter optional.
  • Breaking: Change MCPBase to accept a StreamChannel<String> instead of a Peer, and construct its own Peer.
  • Breaking: Add protocolLogSink optional parameter to connect methods on MCPClient.
  • Breaking: Move channel parameter on MCPServer.new to a positional parameter for consistency.

0.1.0

  • Initial release, supports all major MCP functionality for both clients and servers, at protocol version 2024-11-05.
  • APIs may change frequently until the 1.0.0 release based on feedback and needs.