mcp.json

mcp.json (often committed as .mcp.json) is the configuration file that tells an AI coding assistant or agent which Model Context Protocol servers to connect to and how to launch or reach them. Each entry names a server and supplies its command, arguments, transport, and environment — turning a loose collection of MCP tools into a declared, versionable part of a project. It is the small but load-bearing file that wires an agent to the APIs, files, and services it is allowed to use.

• Server declarations - Lists each MCP server with its launch command or URL, transport, and any required environment variables.
• Project-scoped and portable - Living in the repo as .mcp.json, it travels with the codebase so every contributor’s agent sees the same tools.
• Client-agnostic - The same shape is consumed by a range of MCP-aware clients and coding assistants.
• A configuration contract, not a protocol - It configures MCP connections; the wire behavior itself is defined by the Model Context Protocol.

In practice mcp.json is where agent capability gets governed at the project level — reviewers can see exactly which servers, and therefore which APIs and data, an assistant may reach, and changes flow through normal code review. As MCP adoption grows it becomes a natural control point for security and governance, sitting alongside a server’s own description formats like mcpdesc to define both what an agent connects to and what those connections expose.