Zod

To declare a data type called Hello with methods messages and send, put the following in a .ts file:

import { z } from "zod/v4";

export const api = {
  Hello: {
    state: {
      messages: z.array(z.string()).default(() => []).meta({ tag: 1 }),
    },
    methods: {
      messages: {
        kind: "reader",
        request: {},
        response: {
          messages: z.array(z.string()).meta({ tag: 1 }),
        },
      },
      send: {
        kind: "writer",
        request: {
          message: z.string().meta({ tag: 1 }),
        },
        response: z.void(),
      },
    },
  },
};

important

Reboot requires zod/v4.

Depending on its kind, a method might be able to only read (e.g., reader) or both read and write (e.g., writer) the state.

In the example above, Hello has just one reader and one writer method, but it can have any number of reader, writer, transaction, and workflow methods.

To learn more about how you implement each data type's methods see Implementing your API.