client

Procedures as data for TypeScript. You define a procedure one time: a path, a Zod input, a Zod output and a handler. Then you use it in the same process, over HTTP or WebSocket, from the mark CLI, or from Claude as an MCP tool. A program is plain JSON: calls, references to earlier results, and control flow. The client gives streams, middleware, retries and a cache.

The site has the Composer (build a program from blocks, then start it in your browser), the middleware lab, the procedure catalog and the status board.

Install

npm install @procedures/client zod

The packages need Node.js 22 or later. They are ES modules.

Example

import { z } from "zod";
import { Client, LocalTransport, PROCEDURE_REGISTRY, allCoreProcedures, createProcedure, zodAdapter } from "@procedures/client";
import "@procedures/client/register"; // the control flow: client.chain and the others

// A procedure: a path, a typed input and output, and a handler
PROCEDURE_REGISTRY.register(
  createProcedure()
    .path(["greet"])
    .input(zodAdapter(z.object({ name: z.string() })))
    .output(zodAdapter(z.string()))
    .handler(async ({ name }) => `Hello, ${name}!`)
    .build(),
);
for (const p of allCoreProcedures) if (!PROCEDURE_REGISTRY.has(p.path)) PROCEDURE_REGISTRY.register(p);

const client = new Client(new LocalTransport({ registry: PROCEDURE_REGISTRY }));
console.log(await client.exec({ $proc: ["greet"], input: { name: "Ada" } }));
// Hello, Ada!

// A program is JSON: the second step reads the result of the first step
const result = await client.exec({
  $proc: ["client", "chain"],
  input: {
    steps: [
      { $proc: ["client", "add"], input: { a: 2, b: 3 } },
      { $proc: ["client", "multiply"], input: { a: { $ref: "$last" }, b: 4 } },
    ],
  },
});
console.log(result.final);
// 20

Replace LocalTransport with HttpTransport or WebSocketTransport to use the same procedures on a server. PROGRAM-FORMAT.md tells the rules of programs.

Compared with other tools