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MCP

MCP stands for Model Context Protocol.

In Arc, MCP is the easiest way to connect external tool servers without writing Arc-specific integration code.

What MCP Is For

Use MCP when you want Arc to access tools from:

  • GitHub or other developer services
  • external file or database servers
  • internal automation servers
  • any service that already exposes an MCP server

How Arc Uses MCP

You configure servers in:

  • ~/.arc/mcp.json

Arc discovers those servers and exposes them through a gateway layer.

From the model's point of view, the main entry points are:

  • mcp_list_tools
  • mcp_call

That keeps the model surface small even when you connect many MCP servers.

Example Config

{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": { "GITHUB_TOKEN": "ghp_xxx" }
    },
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/dir"]
    }
  }
}

Remote SSE servers are also supported.

How To Check MCP In Arc

Use:

/mcp

That shows configured server status.

Use:

/skills

to see the MCP gateway alongside the rest of Arc's capabilities.

When To Prefer MCP Over A Skill

Prefer MCP when:

  • the tool already exists as an MCP server
  • multiple clients may share the same tool server
  • you want a cleaner boundary between Arc and the external system
  • the integration should stay provider-agnostic

Prefer a local Arc skill when the behavior is tiny, local, or very Arc-specific.