mcp-server

functype-mcp-server

MCP server for functype — documentation lookup and compile-time TypeScript code validation for AI editors.

This package is part of the functype monorepo.

Features

• search_docs — Search functype documentation by keyword or type name
• get_type_api — Detailed API reference for any type (Option, Either, List, IO, etc.)
• get_interfaces — Interface hierarchy (Functor, Monad, Foldable, Extractable, etc.)
• validate_code — Type-check functype code snippets using the TypeScript Compiler API
• set_functype_version — Switch functype version at runtime (installs + reloads docs and types)

The validate_code tool is the killer feature: an LLM writes functype code, calls the tool, gets back type errors, and fixes them before showing the user.

Installation

Claude Desktop

Add to your Claude Desktop config (~/Library/Application Support/Claude/claude_desktop_config.json):

{
  "mcpServers": {
    "functype": {
      "command": "npx",
      "args": ["functype-mcp-server"]
    }
  }
}

Claude Code

Add to your project's .mcp.json:

{
  "mcpServers": {
    "functype": {
      "command": "npx",
      "args": ["functype-mcp-server"]
    }
  }
}

From Source

git clone https://github.com/jordanburke/functype.git
cd functype/mcp-server
pnpm install
pnpm build

Then configure your MCP client to use node dist/bin.js.

Tools

search_docs

Search functype documentation. Omit query for a full overview.

query?: string  — Type name or keyword (e.g., "Option", "map", "Foldable")

get_type_api

Get detailed API reference for a specific type.

type_name: string              — e.g., "Option", "Either", "List", "IO"
include_full_interface?: bool  — Include full TypeScript interface definition

get_interfaces

Get the interface hierarchy — Functor, Monad, Foldable, Extractable, etc.

No parameters.

validate_code

Type-check a functype code snippet using the TypeScript compiler.

code: string          — TypeScript code to validate
auto_import?: bool    — Auto-import functype types if no import present (default: true)

Returns Validation PASSED or a list of errors with line, column, message, and TS error code.

set_functype_version

Switch the functype version at runtime. Installs the specified version and reloads all documentation and type definitions.

version: string  — Version to install (e.g., "0.47.0", "latest", ...)

Requires functype >= 0.47.0 for full documentation support. Older versions will still work for type-checking via validate_code.

Environment Variables

Variable	Default	Description
TRANSPORT_TYPE	stdio	Transport mode: stdio or httpStream
PORT	3000	HTTP port (when using httpStream)
HOST	127.0.0.1	HTTP host (when using httpStream). Set 0.0.0.0 to bind all interfaces

Security note. set_functype_version installs a package and dynamic-imports it, so it is only registered when TRANSPORT_TYPE=stdio (the default). Over HTTP, an unauthenticated caller could otherwise downgrade functype to a vulnerable version. The HTTP listener also defaults to 127.0.0.1 — set HOST=0.0.0.0 explicitly if you really want to bind publicly, and front it with auth.

Development

pnpm validate          # format + lint + typecheck + test + build
pnpm test              # Run tests
pnpm inspect           # Build + launch MCP Inspector
pnpm serve:dev         # Dev server with tsx watch

License

MIT