MCP-Haskell
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A complete Model Context Protocol (MCP) implementation for Haskell, supporting both StdIO and HTTP transport.
Details
- Author
- tritlo
- Categories
- Developer Tools, API
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Setup
Install MCP-Haskell in your MCP client (Claude Desktop, Cursor, Windsurf, and others).
Repository: https://github.com/tritlo/mcp
Follow the installation instructions in the repository README, then restart your MCP client.
MCP — Model Context Protocol for Haskell
A complete implementation of theModel Context Protocol (MCP)for Haskell, split into two packages:
- mcp-types— Pure protocol types with minimal dependencies (aeson, base, containers, text)
- mcp— Servant-based HTTP server with JWT authentication
This repository provides a type-safe implementation of the Model Context Protocol in Haskell. MCP is an open protocol that standardizes how applications provide context to Large Language Models (LLMs), enabling AI models to securely connect to data sources and tools.
- Latest Protocol Support: Implements MCP protocol version 2025-06-18
- Complete MCP Protocol Implementation: All MCP message types, requests, responses, and notifications
- Type-Safe Design: Full Haskell type system integration with automatic JSON serialization via Aeson
- HTTP Transport: Servant-based HTTP server with streaming SSE responses
- JWT Authentication: Secure authentication viaservant-auth-server
- Extensible Server Interface: Configurable handler framework for implementing custom MCP servers
- Tool Framework: Helper functions for defining tools with input validation and structured results
The implementation is organized into two packages:
Core protocol types with minimal dependencies — suitable for building clients or alternative server implementations.
- MCP.Types: Core MCP data types (Content, Resource, Tool, Prompt, Capability, etc.)
- MCP.Protocol: JSON-RPC 2.0 message wrappers, all client/server request/response types, notification types
- MCP.Aeson: Custom Aeson parsing options
Servant-based server implementation. Re-exportsMCP.ProtocolandMCP.Typesfor convenience.
- MCP.Server: Core server infrastructure withMCPServerTmonad transformer,ProcessHandlersrecord,ToolHandlerframework, JWT-authenticated Servant API, server state management and request routing
For OAuth 2.0 authorization in MCP clients, seeoauth2-server.
For a server implementation, addmcpto yourbuild-depends:
build-depends: base , servant , servant-server , servant-auth-server , aeson , mcp
If you only need the protocol types (e.g. for a client), depend onmcp-typesinstead:
This project targets GHC 9.12 (seecabal.project).
{-# LANGUAGE DataKinds #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE TypeFamilies #-} import Control.Concurrent.MVar (newMVar) import MCP.Server -- Define your handler state and user types type instance MCPHandlerState = () type instance MCPHandlerUser = MyUser -- Create server state with capabilities mkServerState :: IO (MVar MCPServerState) mkServerState = do let impl = Implementation "my-server" "1.0.0" Nothing caps = ServerCapabilities { logging = Nothing , prompts = Nothing , resources = Nothing , tools = Just (ToolsCapability { listChanged = Just True }) , completions = Nothing , experimental = Nothing } handlers = withToolHandlers myTools defaultProcessHandlers newMVar $ initMCPServerState () Nothing Nothing caps impl Nothing handlers -- Define tools using the ToolHandler framework myTools :: [ToolHandler] myTools = [ toolHandler "greet" (Just "Say hello") greetSchema $ \_args -> return $ ProcessSuccess $ toolTextResult ["Hello!"] ]
A fully documented example server lives inmcp-server/example/. It demonstrates every major feature: tools, resources, resource templates, prompts, completions, logging, lifecycle hooks, and JWT authentication.
The server starts onhttp://localhost:8080/mcpand prints a JWT bearer token to stdout. Use it in theAuthorizationheader for all requests:
# Initialize the session (replace $TOKEN with the printed token) curl -s -X POST http://localhost:8080/mcp \ -H 'Content-Type: application/json' \ -H "Authorization: Bearer $TOKEN" \ -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"curl","version":"1.0"}}}' # Send initialized notification curl -s -X POST http://localhost:8080/mcp \ -H 'Content-Type: application/json' \ -H "Authorization: Bearer $TOKEN" \ -d '{"jsonrpc":"2.0","method":"notifications/initialized","params":null}' # List available tools curl -s -X POST http://localhost:8080/mcp \ -H 'Content-Type: application/json' \ -H "Authorization: Bearer $TOKEN" \ -d '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' # Call the add tool curl -s -X POST http://localhost:8080/mcp \ -H 'Content-Type: application/json' \ -H "Authorization: Bearer $TOKEN" \ -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"add","arguments":{"a":17,"b":25}}}'
Seemcp-server/example/SKILL.mdfor curl examples covering all 15 endpoints.
mcp-types/ # Core protocol types package ├── src/MCP/ │ ├── Aeson.hs # Custom Aeson parsing options │ ├── Protocol.hs # JSON-RPC protocol messages │ └── Types.hs # Core MCP data types └── mcp-types.cabal mcp-server/ # Server implementation package ├── src/MCP/ │ ├── Server.hs # Re-exports Common, HTTP, and Stdio │ └── Server/ │ ├── Common.hs # Types, state, request routing, tool helpers │ ├── HTTP.hs # Servant-based HTTP transport with JWT auth │ └── Stdio.hs # Stdio transport ├── test/ │ ├── Main.hs # Test entry point │ └── MCP/ │ ├── Integration.hs # HTTP integration tests (hspec-wai) │ ├── StdioIntegration.hs # Stdio integration tests │ ├── TestServer.hs # Test server configuration │ └── TestUtils.hs # Test utilities and request builders ├── example/ │ ├── Main.hs # Example server (tools, resources, prompts, etc.) │ ├── mcp-example.cabal # Standalone cabal project │ ├── mcp-config.json # Claude Desktop MCP configuration template │ └── SKILL.md # Build, run, and test instructions └── mcp.cabal
MPL-2.0 — seeLICENSEin this repository.
- Model Context Protocol Specification
- MCP TypeScript SDK
- Official MCP Documentation
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