Adding MCP tools to an agent

MCP is the standard way for an agent to call an external tool. It turns a database, a CRM, an API or an observability platform into a function with typed inputs and outputs that the agent can invoke. There are two ways to add one.

The MCP Marketplace

Go to Settings → MCP Marketplace. It is powered by Composio and covers hundreds of SaaS integrations including Linear, Notion, GitHub, Stripe and Salesforce. Installation is OAuth and one click, with no JSON to write. Start here.

Custom MCP configs

For an internal tool the Marketplace does not cover, go to Settings → Artifacts → New MCP Config and write the JSON yourself. Two server types are supported.

A local subprocess over stdio:

{
  "mcpServers": {
    "tool-name": {
      "command": "npx",
      "args": ["@modelcontextprotocol/server-linear"],
      "env": { "API_KEY": "value" }
    }
  }
}

A remote endpoint over HTTP:

{
  "mcpServers": {
    "tool-name": {
      "type": "http",
      "url": "https://endpoint.example.com",
      "headers": { "Authorization": "Bearer token" }
    }
  }
}

Credentials in a config

Credentials can go directly in the JSON, because the MCP server runs in a separate proxy sidecar rather than inside the agent. Tick Mark as sensitive when the config contains any. The dashboard then hides the JSON after saving, so editing it means pasting the whole thing again. Treat edit access to the dashboard as production access.

How it runs on managed agents

A sidecar called mcp-proxy fetches the attached configs at startup, spawns the stdio subprocesses, forwards the HTTP requests, and restarts anything that crashes with exponential backoff. It exposes one uniform endpoint per server at http://mcp-proxy.internal:8081/servers/<name>/mcp. The agent can call the tools but never reads the credentials or the config.

The self-hosted difference

On a self-hosted runtime without mcp-proxy, configs are written to local files, so those credentials sit on the agent's filesystem. Plan for that before you put a production key in one.

Attaching to an agent

Open the agent in Fleet, go to MCP Configs, select the configs you want, then Save & Redeploy. An agent can have several.