MCP Servers

MCP (Model Context Protocol) servers expose tools that agents can call. Register a server in your config, and the daemon discovers its tools automatically. Add a filesystem server, a database client, a code interpreter — any MCP-compatible server works.

Configuration

Stdio transport

The daemon spawns the server as a child process:

[mcps.filesystem]
command = "npx"
args = ["-y", "@modelcontextprotocol/server-filesystem", "/home/user/docs"]
env = { NODE_ENV = "production" }
auto_restart = true

HTTP transport

The server runs independently, daemon connects to it:

[mcps.my-api]
url = "http://localhost:8080/mcp"

Use stdio for local tools. Use HTTP when the server runs on a different machine or needs to persist across daemon restarts.

Tool discovery

When the daemon starts (or when config changes are hot-reloaded), it connects to each MCP server, queries its tool schemas, and registers them in the tool registry. Agents can then call these tools like any built-in tool.

If a server is unavailable, its tools are still registered but return errors when called. The daemon doesn't crash — it degrades gracefully.

Scoping

Restrict which agents can use which MCP servers:

[agents.researcher]
mcps = ["search"]          # only search tools

[agents.writer]
mcps = []                  # no MCP tools at all

Empty list means access to all MCP servers.

MCP servers vs. commands

These are related but different:

• MCP servers are tool providers. The daemon connects to them and calls their tools.
• Commands (like crabtalk search) are standalone binaries. They can be MCP servers (search is), or they can be clients that connect to the daemon (telegram is).

A command that runs as an MCP server is just a convenient way to install and manage the server binary. The MCP protocol is the same either way.

Hot-reload

Add, remove, or modify MCP server configs without restarting the daemon. Save crab.toml and the daemon picks up changes automatically.

What's next

• Build an MCP Server — create your own tool server
• Commands — cargo-style dispatch and service management
• Configuration — full config reference