Skip to content
Lumit docs Lumit docs

Make

Updated

MCP

A program edits a project by starting lumit-cli mcp and talking to it over standard input and output. Each message is one line of JSON-RPC 2.0, as the Model Context Protocol (MCP) sets out. Each of Lumit’s commands is a tool, named with _ for .: comp.list is comp_list. Setting an MCP client up to use Lumit is in Command line.

A first program

Section titled “A first program”

drive.mjs renders a half-size frame of every composition in a project, with Node.js:

import { spawn } from "node:child_process";
import { createInterface } from "node:readline";


const [cli, project] = process.argv.slice(2);
const lumit = spawn(cli, ["mcp", "--project", project], {
  stdio: ["pipe", "pipe", "inherit"],
});


const waiting = new Map();
let next = 1;
createInterface({ input: lumit.stdout }).on("line", (line) => {
  const message = JSON.parse(line);
  waiting.get(message.id)?.(message);
  waiting.delete(message.id);
});


function write(message) {
  lumit.stdin.write(JSON.stringify(message) + "\n");
}


function send(method, params) {
  const id = next++;
  write({ jsonrpc: "2.0", id, method, params });
  return new Promise((done) => waiting.set(id, done));
}


async function tool(name, args) {
  const { result } = await send("tools/call", { name, arguments: args });
  const text = result.content[0].text;
  if (result.isError) throw new Error(text);
  return JSON.parse(text);
}


await send("initialize", {
  protocolVersion: "2025-06-18",
  capabilities: {},
  clientInfo: { name: "drive", version: "1.0.0" },
});
write({ jsonrpc: "2.0", method: "notifications/initialized" });


const { comps } = await tool("comp_list", {});
for (const comp of comps) {
  const frame = await tool("comp_frame", { comp: comp.id, scale: 0.5 });
  console.log(comp.name, frame.path);
}
lumit.stdin.end();
node drive.mjs <path to lumit-cli> stripes.lum

Each frame is written beside the project. Closing standard input ends lumit-cli.

What the program sees

Section titled “What the program sees”
  • tools/list answers every tool with a JSON schema of its arguments. The Scripting reference lists the same commands.
  • A tool’s answer is one text item holding the command’s answer as JSON. comp_frame adds an image item with the PNG when it is 2 MB or smaller.
  • A command that fails answers isError: true, and the text is the reason.
  • script_run takes { "source": "..." } and runs JavaScript as one undo step, with the lumit object of Scripts.
  • Nothing is saved until project_save is called.

The limits on files, saves and exports are in Command line. Without --project, lumit-cli mcp edits the project open in Lumit instead, once Settings ▸ General ▸ Let other programs drive Lumit is on.

Section titled “Related”