MCP

Connect MCP servers to Pi so the agent can call their tools.

@pi-unipi/mcp · part of UniPi

MCP (Model Context Protocol) is a standard way for a server to give tools to an AI agent. Examples are GitHub operations, database queries and file access.

What it does

• Starts each enabled MCP server at session start and registers its tools as Pi tools.
• Names each tool <server>__<tool>, for example github__search_code.
• Lets you browse a server catalog and add a server from a TUI overlay.
• Reads server configs from a global folder and a project folder. The project config wins.
• Limits each tool result to 64 KiB of text. It saves the full text of a larger result to a file.
• Supports 20 servers at most.

Quick start

UniPi installs this package:

pi install npm:@pi-unipi/unipi

To install this package alone:

pi install npm:@pi-unipi/mcp

To add a server:

1. Open /unipi:settings.
2. Select the MCP group.
3. Select Add server….
4. Search the catalog and select a server. You can also paste a custom config.
5. Edit the JSON config in the right pane. Save it.
6. Restart Pi.

Commands

The MCP group in /unipi:settings has four actions:

Agent tools

This package has no fixed tools. Each running server adds its own tools.

github__search_code({ query: "authentication middleware" })
filesystem__read_file({ path: "/home/user/config.json" })

Configuration

Each folder can hold two files:

• mcp-config.json holds the server definitions. UniPi writes it with mode 0600.
• config.json holds the enabled state of each server.

mcp-config.json uses the common MCP format that Claude Desktop and Cursor also use:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/home/user/projects"]
    }
  }
}

Merge rules:

1. A server in one folder only loads as defined.
2. A server in both folders uses the project definition.
3. A server with "enabled": false in the project config.json does not start.

How it works

At session start, all enabled servers connect at the same time. Each request to a server has a 10-second timeout. When all servers finish, the package registers the tools of the good servers in one sorted list. A server that fails does not add tools.

The package sorts the keys in each tool schema. Thus the tool list is the same from one run to the next, and the provider can reuse its prompt cache. Refer to Prefix cache.

Pi cannot remove a tool during a session. Thus a change to a server takes effect at the next Pi start.

When a result is more than 64 KiB, the agent gets the start and the end of the text. If the full text is 16 MiB or less, the package writes it to ~/.unipi/tool-results/ with mode 0600. The result gives the file path, so the agent can use read to see the rest.

The catalog file is ~/.unipi/config/mcp/servers.json. If this file does not exist, the package uses a list of 49 servers that ships with it.

The Info Screen shows an MCP Servers group with total, active and failed servers and the tool count.

Troubleshooting

• A server does not start. Run /unipi:mcp-status to see the error. Make sure that the server command is on your PATH.
• New tools do not show. Restart Pi.
• The sync fails. Examine your network. The 49-server list stays available.

See also

• Prefix cache
• Commands reference
• Info Screen