README
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CallToolResult
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CancellationToken
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CompletionResult
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mcp

Type-safe MCP SDK in MoonBit with server/client support and dual transport (STDIO/HTTP)

mcp

modelcontextprotocol

Download zip

Author

colmugx

Version

0.18.2

License

Apache-2.0

Repository

github.com/colmugx/mcp.mbt

Last updated

11 hours ago

Downloads

#MoonBit MCP SDK

Type-safe Model Context Protocol SDK for MoonBit.

Version: 0.18.1 · Protocol: 2026-07-28 (stateless) · License: Apache-2.0

#Protocol support and scope

The SDK targets MCP 2026-07-28 with stateless per-request metadata and MRTR. This branch includes complete content/tool/resource/prompt wire models, completion, sampling and form/URL elicitation models, trusted request context, cooperative cancellation, cache metadata preservation, and registry-aware HTTP header validation. Registering features controls the capabilities advertised by discovery; an empty registry must be enabled explicitly.

Tool input/output validation now compiles schemas once at registration and rejects invalid arguments before executing handlers. Successful structured output is validated when an output schema is declared. Closed objects, precise numeric constraints, local and preloaded external $ref, $id/anchors, dynamic references, unevaluated constraints, and standard-vocabulary custom dialects are supported. Pass schema_resources to tool_definition for external documents; registration never fetches them over the network.

Elicitation forms are validated before interaction and accepted content is checked against an owned schema snapshot. The server independently verifies MRTR response keys, result types, and form constraints from authenticated continuation state; the client bounds retries without a final unconsumable interaction.

JSON-RPC ids and peer error codes now retain exact integer literals beyond Int32 and binary64. String ids, large numeric ids, duplicate checks, subscriptions and cancellation share consistent routing without truncation.

Conformance is evidence-based, not an unconditional complete-protocol guarantee. The validator's standard suite reaches 1301/1301, but optional format assertions and general ECMA-262 patterns remain outside its supported profile. MCP transport/runtime evidence and host responsibilities are tracked separately in the conformance matrix and migration notes. The error API uses MoonBit checked errors rather than Result-valued failure returns.

Bearer tokens, server-side authentication hooks, and protected-resource metadata are supported. OAuth authorization client lifecycle, PKCE, dynamic client registration, and token refresh management are not included.

#Installation

Install the published SDK and its async runtime dependency in your MoonBit project:

moon add colmugx/mcp@0.18.0
moon add moonbitlang/async@0.21.0

Development can use the workspace's independent external/json-schema submodule. The SDK currently declares colmugx/json-schema@0.1.4; workspace and historical registry-only verification evidence are recorded separately in the conformance notes.

#Quick Start

#Server

async fn main {
  @mcp.MCPServer::MCPServer("demo-server", "1.0.0")
    .tool("echo", "Echo text", Json::object({ "type": "object" }), fn(_context, args) {
      let text = match args {
        Object(obj) =>
          match obj.get("text") {
            Some(String(value)) => value
            _ => ""
          }
        _ => ""
      }
      Ok(@mcp.ToolResult::text(text))
    })
    .run_stdio()
}

Use .run_http(port=4240, path="/mcp") for Streamable HTTP.

#Client

async fn main {
  let client = @mcp.MCPClient::connect_http(
    url="http://localhost:4240/mcp",
    name="demo-client",
    version="1.0.0",
  )
  defer client.close()
  // Optional one-shot discovery of server identity/capabilities.
  ignore(client.discover())
  let result = client.list_tools()
  for tool in result.tools { println(tool.name) }
}

Connection and operation APIs return their success values directly and raise MCPError on failure. Use try ... catch for local recovery; async cancellation remains an async error. Business handler callbacks still return explicit Result values. See the client error-handling guide. For local subprocess servers, use MCPClient::connect_stdio(cmd~, args?, name~, version~, extra_env?, group~).

#Host

async fn main {
  let host = @mcp.MCPHost::MCPHost(name="my-host", version="1.0.0")
  @async.with_task_group(group => {
    defer host.close_all()
    ignore(host.connect_stdio(name="local", cmd="moon", args=["run", "server"], group~))
    ignore(host.connect_http(name="remote", url="http://localhost:4240/mcp"))
    let result = host.list_tools()
    for tool in result.tools { println(tool.name) } // local.echo
    ignore(host.call_tool("local.echo", arguments="{\"text\":\"hello\"}"))
  })
}

Host tool names are qualified as connection.tool so multiple servers can expose the same tool name without collision.

#Documentation

Document	Description
Quickstart	Server, client, and host setup
Protocol Types	JSON-RPC, errors, and MCP types
Server Guide	High-level server API and runtime behavior
Transport Reference	Advanced transport internals
Client Guide	Connections, MRTR input handlers, notifications, and legacy compatibility
Architecture	Protocol, runtime, transport, application layers
Host Guide	MCPHost named connections and routing
Conformance notes	Protocol coverage, remaining gaps, and compatibility notes
Changelog	Release history and breaking changes

#API Direction

The default public path is intentionally small:

MCPServer for serving tools, resources, and prompts.
MCPClient for one server connection.
MCPHost for multiple named server connections.
colmugx/mcp/client/legacy for talking to 2025-11-25-era servers (LegacyClient).

Transports and request builders are advanced/internal details. Existing low-level imports may still be useful for SDK contributors, but application code should prefer the high-level APIs above.

#License

Apache-2.0

mcp

#MoonBit MCP SDK

#Protocol support and scope

#Installation

#Quick Start

#Server

#Client

#Host

#Documentation

#API Direction

#License

#Annotations

#CacheScope

#CallToolResult

#CancellationToken

#ClientCapabilities

#CompleteRequestParams

#CompletionArgument

#CompletionContext

#CompletionReference

#CompletionRegistry

#CompletionResult

#ContentBlock

#ContentMetadata

#CreateMessageRequest

#CreateMessageResult

#DiscoverResult

#ElicitationAction

#ElicitationCapabilities

#ElicitationRequest

#ElicitationResult

#ElicitationValue

#GetPromptResult

#Icon

#IconTheme

#InputRequestEntry

#InputRequestKind

#JsonInteger

#JsonNumber

#JsonRpcRequest

#JsonSchema

#ListPromptsResult

#ListResourcesResult

#ListToolsResult

#MCPClient

#MCPError

#MCPHost

#MCPServer

#ModelHint

#ModelPreferences

#ParamDef

#Params

#Principal

#ProgressNotification

#ProgressReporter

#ProgressToken

#PromptArgument

#PromptCapabilities

#PromptDefinition

#PromptMessage

#ReadResourceResult

#RequestCancelled

#RequestContext

#RequestId

#ResourceCapabilities

#ResourceContents

#ResourceData

#ResourceDefinition

#ResourceLinkData

#ResourceReadResult

#ResourceTemplateDefinition

#ResultMetadata

#Role

#RootCapabilities

#SamplingCapabilities

#SamplingContent

#SamplingContentBlock

#SamplingContext

#SamplingMessage

#ServerCapabilities

Annotations

CacheScope

CallToolResult

CancellationToken

ClientCapabilities

CompleteRequestParams

CompletionArgument

CompletionContext

CompletionReference

CompletionRegistry

CompletionResult

ContentBlock

ContentMetadata

CreateMessageRequest

CreateMessageResult

DiscoverResult

ElicitationAction

ElicitationCapabilities

ElicitationRequest

ElicitationResult

ElicitationValue

GetPromptResult

Icon

IconTheme

InputRequestEntry

InputRequestKind

JsonInteger

JsonNumber

JsonRpcRequest

JsonSchema

ListPromptsResult

ListResourcesResult

ListToolsResult

MCPClient

MCPError

MCPHost

MCPServer

ModelHint

ModelPreferences

ParamDef

Params

Principal

ProgressNotification

ProgressReporter

ProgressToken

PromptArgument

PromptCapabilities

PromptDefinition

PromptMessage

ReadResourceResult

RequestCancelled

RequestContext

RequestId

ResourceCapabilities

ResourceContents

ResourceData

ResourceDefinition

ResourceLinkData

ResourceReadResult

ResourceTemplateDefinition

ResultMetadata

Role

RootCapabilities

SamplingCapabilities

SamplingContent

SamplingContentBlock

SamplingContext

SamplingMessage

ServerCapabilities

ServerInfo

Tool

ToolAnnotations

ToolCallOutcome

ToolCapabilities

ToolChoice

ToolChoiceMode

ToolDefinition

ToolError

ToolResult

ToolResultContent