Effect

A Model Context Protocol (MCP) server dedicated to fetching the most current documentation from the Effect ecosystem.

Purpose

This MCP server provides real-time access to Effect documentation for AI assistants and tools. It enables VS Code extensions and other MCP clients to retrieve accurate and up-to-date Effect package documentation to assist developers with questions about:

• The core effect package
• Ecosystem packages (@effect/platform, @effect/ai, etc.)
• Both stable and unstable Effect packages

The server intelligently detects imported Effect packages in your code and fetches the most relevant documentation to answer your queries.

Features

• Real-time documentation access for Effect ecosystem
• Support for both stable and experimental packages
• Context-aware package detection based on imports
• Seamless integration with VS Code and other MCP-compatible clients
• Helps answer API usage questions for Effect developers

What this server exposes

• Resources (preferred)
  • Dynamic template: effect-docs://{libId}
  • Completions on {libId} and resource listing are supported
  • Static aliases for discovery: effect-docs://effect, effect-docs://@effect-platform, etc.
  • Supported libraries (as of now):
    • effect
    • @effect/platform
    • @effect/sql
    • @effect/vitest
    • @effect/ai
    • @effect/cli
    • @effect/cluster
    • @effect/rpc
    • @effect/typeclass
• Tools (for compatibility)
  • effect-documentation: fetch docs for selected libraries and return concatenated markdown
  • effect-doc-links: return plain URIs to the resources above so clients can follow them

Caching & Retry

• In-memory TTL cache (~10 minutes) to avoid refetching unchanged docs.
• Lightweight retry with small backoff on transient fetch errors.

Installation

pnpm add @niklaserik/effect-mcp

Usage

For usage in VS Code or other MCP clients, refer to the client's documentation for adding custom MCP servers.

Quick test locally:

pnpm install
pnpm build
node dist/index.js # stdio transport

Then connect with an MCP client (e.g., MCP Inspector) over stdio and try:

• List resources and read effect-docs://effect
• Call tool effect-doc-links with { "libraries": ["effect", "@effect/platform"] }

Initialization instructions

• The server publishes short usage instructions via MCP initialize for clients that display them.

Development

# Install dependencies
pnpm install

# Build the project
pnpm build

# Run in development mode with auto-reload
pnpm dev

Notes:

• Built with @modelcontextprotocol/sdk@^1.17.4 using the modern registerResource/registerTool APIs.
• Transport: stdio by default; can be adapted to Streamable HTTP if needed.

License

MIT