MCP — calling agent tools from rules

MCP (Model Context Protocol) is how AI agents and tool servers talk. The chassis speaks it outbound today: a rule can call a tool on any MCP server with one EXEC.

WHEN .question != ""
WITH mode = "async"
EXEC "mcp+https://mcp.deepwiki.com/mcp#ask_question"

The URL is the MCP server endpoint; the #fragment names the tool. The op’s input becomes the tool call’s arguments; the tool’s result merges into the document like any other op. Because agent tools are often slow, WITH mode = "async" and "continuable" both work — a long-running tool is just a continuation.

Working example: examples/mcp-quickstart/ (rules calling DeepWiki). The txco demo curriculum has a live MCP track.

Probing a server

txco mcp doctor https://mcp.example.com/mcp

Runs the initialize handshake and prints the server’s tool list — the fastest way to find the right #tool-name and check reachability.

The other direction

Exposing a stack’s rules as MCP tools (so Claude or another agent can call your flow) is not shipped as a chassis gateway yet. What exists today: rules can implement the JSON-RPC protocol themselves — examples/mcp-server/ is a working MCP server written entirely in txcl. Treat the gateway form as roadmap; the example as the current pattern.