MCP (Model Context Protocol)

MCP (Model Context Protocol)

MCP is an open standard for connecting AI models to external services. Skill Compose uses MCP to extend agent capabilities beyond built-in tools — adding web search, Git operations, URL fetching, and more.

How MCP Works

graph LR
    Agent[SkillsAgent] -->|MCP Protocol| Server1[Git Server]
    Agent -->|MCP Protocol| Server2[Time Server]
    Agent -->|MCP Protocol| Server3[Tavily Server]
    Agent -->|MCP Protocol| Server4[Fetch Server]
    Server1 --> S1T[git_status, git_diff, git_commit, ...]
    Server2 --> S2T[get_current_time, convert_time]
    Server3 --> S3T[tavily_search, tavily_extract, tavily_crawl]
    Server4 --> S4T[fetch]

Each MCP server runs as a separate subprocess that exposes tools via the MCP protocol. The agent discovers available tools at runtime and calls them like built-in tools.

Adding an MCP Server

Click Add Server on the MCP page, then paste the JSON configuration from any MCP server's README:

{
  "server-name": {
    "command": "npx",
    "args": ["package-name"]
  }
}

The dialog accepts the standard MCP JSON format. If the config is wrapped in "mcpServers": { ... } (common in READMEs), it will be auto-unwrapped.

After adding, Skill Compose automatically starts the server process, discovers its tools, and makes them available to agents — no manual schema definitions needed.

Tool Auto-Discovery

When you add a new MCP server, Skill Compose automatically discovers its tools by connecting to the server process and querying it via the MCP SDK.

How it works:

1. Spawns the MCP server as a subprocess
2. Connects via stdio and calls session.list_tools()
3. Saves discovered tool definitions (name, description, inputSchema) to config/mcp.json

When it triggers:

• Automatically after adding a server via the Web UI (fire-and-forget)
• Manually by clicking the refresh button on any server card
• Via API: POST /api/v1/mcp/servers/{name}/discover-tools

API Key Management

Some MCP servers require API keys (e.g. Tavily). The MCP page shows the status of each required key:

• Configured — key is set and ready to use
• From ENV — key is resolved from your .env file
• Not Set — key needs to be configured

Click on a key to set or update its value directly from the UI. Keys are saved to .env and take effect immediately.

Default Servers

These servers are enabled by default and available out of the box:

Git

Version control operations via uvx mcp-server-git.

Time

Timezone utilities via uvx mcp-server-time.

Tavily

AI-optimized web search and content extraction via npx tavily-mcp.

Requires: TAVILY_API_KEY

Fetch

URL fetching and content extraction via uvx mcp-server-fetch.

MCP vs Built-in Tools

:::tip web_fetch and web_search are built-in tools, not MCP. Use them for basic web access without enabling any MCP server. :::

Enabling MCP Servers per Agent

MCP servers are enabled per agent:

1. Go to Agents and select an agent
2. Check the MCP servers you want in the MCP Servers section
3. Save

Default agents include git, time, and tavily.

Configuration File

MCP servers are defined in config/mcp.json:

{
  "mcpServers": {
    "tavily": {
      "name": "Tavily Search",
      "description": "AI-optimized web search and content extraction",
      "command": "npx",
      "args": ["-y", "tavily-mcp@latest"],
      "env": {
        "TAVILY_API_KEY": "${TAVILY_API_KEY}"
      },
      "defaultEnabled": true,
      "tools": [...]
    }
  }
}

Environment variables use ${VAR_NAME} syntax and resolve from your .env file. Multi-worker deployments stay in sync — get_mcp_client() detects mcp.json file changes and auto-reloads.

Creating Custom MCP Servers

Two approaches:

1. Ask the agent — use the mcp-builder skill: "Create an MCP server that queries my PostgreSQL database". The agent will scaffold the code, build it, and register it to config/mcp.json automatically.
2. Paste from README — find any MCP server on npm/PyPI, copy its JSON config, and paste it into the Add Server dialog.

Related

• Tools — Built-in tool reference
• Agents — MCP configuration in agents
• How to: Configure MCP