Haskell Mcp Server

mcp-server

A fully-featured Haskell library for building [Model Context Protocol (MCP)](https://modelcontextprotocol.io/) servers.

Features

• Complete MCP Implementation: Supports MCP 2025-06-18 specification
• Type-Safe API: Leverage Haskell's type system for robust MCP servers
• Multiple Abstractions: Both low-level fine-grained control and high-level derived interfaces
• Template Haskell Support: Automatic handler derivation from data types
• Multiple Transports: STDIO and HTTP Streaming transport (MCP 2025-06-18 Streamable HTTP)

Supported MCP Features

• ✅ Prompts: User-controlled prompt templates with arguments
• ✅ Resources: Application-controlled readable resources
• ✅ Tools: Model-controlled callable functions
• ✅ Initialization Flow: Complete protocol lifecycle with version negotiation
• ✅ Error Handling: Comprehensive error types and JSON-RPC error responses

Quick Start

Add the library `mcp-server` to your cabal file:

build-depends:
  mcp-server

Create a simple module, such as this example below:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}

import MCP.Server
import MCP.Server.Derive

-- Define your data types
data MyPrompt = Recipe { idea :: Text } | Shopping { items :: Text }
data MyResource = Menu | Specials
data MyTool = Search { query :: Text } | Order { item :: Text }

-- Implement handlers
handlePrompt :: MyPrompt -> IO Content
handlePrompt (Recipe idea) = pure $ ContentText $ "Recipe for " <> idea
handlePrompt (Shopping items) = pure $ ContentText $ "Shopping list: " <> items

handleResource :: MyResource -> IO Content
handleResource Menu = pure $ ContentText "Today's menu..."
handleResource Specials = pure $ ContentText "Daily specials..."

handleTool :: MyTool -> IO Content
handleTool (Search query) = pure $ ContentText $ "Search results for " <> query
handleTool (Order item) = pure $ ContentText $ "Ordered " <> item

-- Derive handlers auto