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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
    A unified HTTP interface using StreamableHTTP or Server-Sent Events (SSE)—your agent only needs to talk to one API.

  • Subprocess Communication via stdio
    Tools are launched as subprocesses using the stdio transport defined by the Model Context Protocol (MCP), enabling lightweight, language-agnostic execution.

  • Dynamic Routing & Multiplexing
    MCPX dispatches tool calls based on configuration. Swap tools or scale horizontally without changing client logic.

  • Policy & Access Control Ready
    Tool-level access control via configuration ensures secure usage by agents or users.

  • Zero-Config for Clients
    Clients don’t need to know what tools exist or where they live, just point to MCPX and go.

note

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