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Architecture

If you're new to MCP (Model Context Protocol), we recommend starting with this introduction to get up to speed.

Lunar.dev MCPX is designed as middleware between your client application and one or more MCP-compatible servers. It simplifies integration by acting as a centralized gateway: your client and LLM only need to connect to MCPX, which handles all the communication with backend MCP services transparently.

This architecture helps you manage complexity, enforce consistent access policies, and easily switch or scale backend tools—without changing your client logic.

MCPX Architecture

Key Characteristics​

  • Single Entry Point: MCPX exposes a unified HTTP interface using Server-Sent Events (SSE), allowing your client and LLM to send and receive messages through a consistent API.
  • Process Spawning via stdio: Backend MCP tools are spawned as subprocesses and communicate with MCPX over stdio, in line with the MCP spec.
  • Transparent Multiplexing: MCPX dynamically dispatches requests to the appropriate backend service, so you can manage multiple tools or services with a single configuration.
  • Zero-Config for Clients: No need for your client to manage direct connections to individual tools. Just point it at MCPX and let it handle the rest.
note

MCPX currently supports only MCP Tools as targets (not yet full MCP Apps or multi-user contexts).