Schema and field types

A resource's schema is an ordered list of fields. Each field has a name, a type, and, depending on the type, a small set of options. Field order matters for one specific reason: a template field can only reference a field that appears earlier in the same list — see the template row below.

Field names must start with a lowercase letter and contain only letters, numbers, and underscores. A resource can have at most 30 fields. Every generated record also carries an id automatically — you never define it yourself, and a field you name id is silently ignored in favor of the real one.

Reference table

The template type

template is the one type that reads other fields instead of generating its own value. Its template option is a plain string; anywhere it contains {{fieldName}}, that placeholder is replaced with the value the field named fieldName already generated for this same record. This only works for fields defined earlier in the schema — a template can't reference a field that hasn't run yet. A common use: given a firstName field and a lastName field earlier in the list, a later email field could instead be a template field with "{{firstName}}.{{lastName}}@example.com" to keep an email consistent with a name, rather than generating an unrelated one.

Determinism, briefly

Every field type pulls from the same seeded pseudo-random sequence as every other field on the same record, so the exact same schema, seed, and record index always produce the exact same record, field for field. How generation works covers the mechanism in full; what matters here is that changing a field's options changes that field's future output, but reordering or adding fields elsewhere in the schema does not reshuffle the ids already handed out for existing records — ids are generated independently of the rest of the schema.

Fetching a resource's data

None of this changes how you read the data — every resource, regardless of its fields, is read the same way:

const response = await fetch("https://mocklab.dev/m/demo7k2m9x/products");
const products = await response.json();

import { useQuery } from "@tanstack/react-query";

function ProductList() {
  const { data: products } = useQuery({
    queryKey: ["products"],
    queryFn: () => fetch("https://mocklab.dev/m/demo7k2m9x/products").then((res) => res.json()),
  });

  return <pre>{JSON.stringify(products, null, 2)}</pre>;
}