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

mcp

modelcontextprotocol

moon add colmugx/mcp@0.15.0

Download zip

Author

colmugx

Version

0.15.0

License

Apache-2.0

Repository

github.com/colmugx/mcp.mbt

Last updated

18 hours ago

Downloads

154

Dependencies

README

#MoonBit MCP SDK

Type-safe Model Context Protocol SDK for MoonBit.

Version: 0.15.0 · Protocol: 2026-07-28 (stateless) · License: Apache-2.0

#Installation

moon add colmugx/mcp

#Quick Start

#Server

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

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

#Client

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

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 => {
    ignore(host.connect_stdio(name="local", cmd="moon", args=["run", "server"], group~))
    ignore(host.connect_http(name="remote", url="http://localhost:4240/mcp"))
    match host.list_tools() {
      Ok(result) => for tool in result.tools { println(tool.name) } // local.echo
      Err(e) => println(e.message())
    }
    ignore(host.call_tool("local.echo", arguments="{\"text\":\"hello\"}"))
    host.close_all()
  })
}

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	MCPClient::connect_* and bidirectional mode
Architecture	Protocol, runtime, transport, application layers
Host Guide	MCPHost named connections and routing
Migration 0.15	2025-11-25 → 2026-07-28 migration, node by node
Migration 0.14	Breaking changes from 0.13.x

#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

#
CallToolResult

source

using @colmugx/mcp/client { type CallToolResult }

Client and Host

#
CompletionResult

source

using @colmugx/mcp/client { type CompletionResult }

Client and Host

#
ContentItem

source

using @colmugx/mcp/protocol/types { type ContentItem }

Protocol types

#
JsonRpcRequest

source

using @colmugx/mcp/protocol/types { type JsonRpcRequest }

Protocol types

#
JsonRpcResponse

source

using @colmugx/mcp/protocol/types { type JsonRpcResponse }

Protocol types

#
JsonSchema

source

using @colmugx/mcp/protocol/core { type JsonSchema }

Protocol core

#
ListPromptsResult

source

using @colmugx/mcp/client { type ListPromptsResult }

Client and Host

#
ListResourcesResult

source

using @colmugx/mcp/client { type ListResourcesResult }

Client and Host

#
ListToolsResult

source

using @colmugx/mcp/client { type ListToolsResult }

Client and Host

#
MCPClient

source

using @colmugx/mcp/client { type MCPClient }

Client and Host

#
MCPError

source

using @colmugx/mcp/protocol/types { type MCPError }

Protocol types

#
MCPHost

source

using @colmugx/mcp/client { type MCPHost }

Client and Host

#
MCPServer

source

using @colmugx/mcp/server { type MCPServer }

Server

#
ParamDef

source

using @colmugx/mcp/protocol/tool { type ParamDef }

Protocol tool types

#
Params

source

using @colmugx/mcp/protocol/core { trait Params }

Protocol core

#
ReadResourceResult

source

using @colmugx/mcp/client { type ReadResourceResult }

Client and Host

#
ServerCapabilities

source

using @colmugx/mcp/protocol/types { type ServerCapabilities }

Protocol types

#
ServerInfo

source

using @colmugx/mcp/protocol/types { type ServerInfo }

Protocol types

#
Tool

source

using @colmugx/mcp/protocol/tool { trait Tool }

Protocol tool types

#
ToolCallOutcome

source

using @colmugx/mcp/protocol/tool { type ToolCallOutcome }

Protocol tool types

#
ToolDefinition

source

using @colmugx/mcp/protocol/types { type ToolDefinition }

Protocol types

#
ToolError

source

using @colmugx/mcp/protocol/core { type ToolError }

Protocol core

#
ToolResult

source

using @colmugx/mcp/protocol/tool { type ToolResult }

Protocol tool types

#
TransportError

source

using @colmugx/mcp/protocol/types { type TransportError }

Protocol types

#
get_number

source

fn get_number(json : Json, key : String) -> Result[Double, @colmugx/mcp/protocol/tool.ToolResult
ToolResult]

Extract number from JSON, returning error ToolResult on failure

#
get_optional_number

source

fn get_optional_number(json : Json, key : String) -> Result[Double?, @colmugx/mcp/protocol/tool.ToolResult
ToolResult]

Extract optional number from JSON

#
get_optional_string

source

fn get_optional_string(json : Json, key : String) -> Result[String?, @colmugx/mcp/protocol/tool.ToolResult
ToolResult]

Extract optional string from JSON

#
get_string

source

fn get_string(json : Json, key : String) -> Result[String, @colmugx/mcp/protocol/tool.ToolResult
ToolResult]

Extract string from JSON, returning error ToolResult on failure

#
mcp_server

source

fn mcp_server(name~ : String, version~ : String) -> @colmugx/mcp/server.MCPServer
MCPServer

#
simple_tool

source

fn simple_tool(name : String, description : String, handler : (Json) -> @colmugx/mcp/protocol/tool.ToolResult
ToolResult) -> @colmugx/mcp/protocol/core.ToolWrapper
ToolWrapper

#
tool_fn

source

fn[Args : @colmugx/mcp/protocol/core.Params
Params, Ret : @colmugx/mcp/protocol/core.ToToolResult
ToToolResult] tool_fn(handler : (Args) -> Ret, name~ : String, description~ : String) -> @colmugx/mcp/protocol/core.ToolWrapper
ToolWrapper

Source Files

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mcp

#MoonBit MCP SDK

#Installation

#Quick Start

#Server

#Client

#Host

#Documentation

#API Direction

#License

#CallToolResult

#CompletionResult

#ContentItem

#JsonRpcRequest

#JsonRpcResponse

#JsonSchema

#ListPromptsResult

#ListResourcesResult

#ListToolsResult

#MCPClient

#MCPError

#MCPHost

#MCPServer

#ParamDef

#Params

#ReadResourceResult

#ServerCapabilities

#ServerInfo

#Tool

#ToolCallOutcome

#ToolDefinition

#ToolError

#ToolResult

#TransportError

#get_number

#get_optional_number

#get_optional_string

#get_string

#mcp_server

#simple_tool

#tool_fn

Source Files

#
CallToolResult

#
CompletionResult

#
ContentItem

#
JsonRpcRequest

#
JsonRpcResponse

#
JsonSchema

#
ListPromptsResult

#
ListResourcesResult

#
ListToolsResult

#
MCPClient

#
MCPError

#
MCPHost

#
MCPServer

#
ParamDef

#
Params

#
ReadResourceResult

#
ServerCapabilities

#
ServerInfo

#
Tool

#
ToolCallOutcome

#
ToolDefinition

#
ToolError

#
ToolResult

#
TransportError

#
get_number

#
get_optional_number

#
get_optional_string

#
get_string

#
mcp_server

#
simple_tool

#
tool_fn