MCP-Haskell (hs-mcp)

A Haskell implementation of the Model Context Protocol (MCP).

Overview

MCP-Haskell (hs-mcp) provides a Haskell implementation of the Model Context Protocol, allowing Haskell applications to expose tools, resources, and prompts to MCP-compatible clients like Claude.

Key features:

• Full implementation of MCP protocol
• StdIO transport for local process communication
• JSON-RPC messaging
• Support for resources, tools, and prompts
• Comprehensive test suite

Installation

# Clone the repository
git clone github.com:buecking/hs-mcp.git
cd hs-mcp

# direnv
# echo 'use flake' > .envrc
direnv allow

# nix
nix develop

# Build the project
cabal build

Usage

Creating a simple server

import Network.MCP.Server
import Network.MCP.Types
import Network.MCP.Server.StdIO

main :: IO ()
main = do
  -- Create server
  let serverInfo = Implementation "my-server" "1.0.0"
      serverCapabilities = ServerCapabilities
        { resourcesCapability = Just $ ResourcesCapability True
        , toolsCapability = Just $ ToolsCapability True
        , promptsCapability = Nothing
        }
  
  server <- createServer serverInfo serverCapabilities
  
  -- Register resources (optional)
  let resource = Resource 
        { resourceUri = "my://resource"
        , resourceName = "My Resource"
        , resourceDescription = Just "Description"
        , resourceMimeType = Just "text/plain"
        , resourceTemplate = Nothing
        }
  
  registerResources server [resource]
  
  -- Register resource read handler
  registerResourceReadHandler server $ \request -> do
    -- Implement resource reading logic
    ...

  -- Register tools (optional)
  let tool = Tool 
        { toolName = "my-tool"
        , toolDescription = Just "My tool"
        , toolInputSchema = "{...}" -- JSON schema
        }
  
  registerTools server [tool]
  
  -- Register tool call handler
  registerToolCallHandler server $ \request -> do
    -- Implement tool execution logic
    ...
  
  -- Start the server with StdIO transport
  runServerWithSTDIO server

Example Server

The project includes an example echo server that demonstrates the MCP functionality:

# Build and run the example server
cabal run mcp-echo-server

You can test it with the MCP Inspector or Claude Desktop.

Testing

Run the test suite:

cabal test

Protocol Compatibility

This implementation follows the Model Context Protocol specification and is compatible with:

• Claude Desktop
• MCP Inspector
• Other MCP clients following the specification

Project Structure

• src/Network/MCP/Types.hs - Core MCP types
• src/Network/MCP/Transport/ - Transport implementations
• src/Network/MCP/Server/ - Server implementation
• Examples/ - Example implementations
• Test/ - Test suite

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the BSD-3-Clause License - see the LICENSE file for details.