jt.toSchema

Declaration. Reconstructs a JSON Schema document from the canonical graph for a registered schema. Returns Record<string, unknown> | undefined - undefined when the schema is not registered. The reconstructed schema reflects the normalized canonical representation, which may differ slightly from the original authored schema.

Use this when you want to verify round-trip fidelity - that the canonical graph preserves all structural semantics from the authored schema. Also useful for producing normalized/canonical versions of schemas for display, debugging, or downstream tooling.

Don't use this when you need the original schema object as-authored (use jt.get instead). get returns the original object reference; toSchema returns a new object reconstructed from the internal graph.

Examples

Example 1: Round-trip an Order schema

import { bookstoreEntities as entities } from './bookstore/index.js';

const reconstructed = jt.toSchema('https://bookstore.example/Order');
console.log(JSON.stringify(reconstructed, null, 2));
// Should match the original OrderSchema structure

Example 2: Verify a composed schema round-trips correctly

import { Compose } from 'json-tology';
import { bookstoreEntities as entities, BookSchema } from './bookstore/index.js';

const BookSummarySchema = Compose.pick(
  BookSchema,
  ['isbn', 'title', 'price'] as const,
  'https://bookstore.example/BookSummary',
);
jt.register(BookSummarySchema);

const roundTripped = jt.toSchema('https://bookstore.example/BookSummary');
// Should contain only isbn, title, price properties
const keys = Object.keys((roundTripped?.properties as object) ?? {});
console.log(keys); // ['isbn', 'title', 'price']

Example 3: Undefined for unregistered schemas

const missing = jt.toSchema('https://bookstore.example/NonExistent');
console.log(missing); // undefined

Comparison

json-tology

jt.toSchema('https://bookstore.example/Book')
// Reconstructed from internal canonical graph

Zod

// Not directly supported  - no JSON Schema reconstruction from Zod's runtime representation.
// Use zodToJsonSchema (third-party) to export JSON Schema.

Valibot

// Use the `@valibot/to-json-schema` companion library:
import { toJsonSchema } from '@valibot/to-json-schema';
const jsonSchema = toJsonSchema(BookSchema);
// Limitation: produces JSON Schema from Valibot's runtime representation;
// no first-class graph reconstruction, and not all Valibot constructs map.

TypeBox + Value

// TypeBox schemas ARE plain JSON Schema  - no reconstruction needed.
// JSON.stringify(BookSchema) gives the schema directly.

AJV

// Not directly supported  - AJV stores compiled validators, not schemas.
// Pass schema directly: JSON.stringify(bookSchema)

Pydantic

Book.model_json_schema()  # Exports JSON Schema from the model class

Related

• jt.get - retrieve the original schema object (not reconstructed)
• Ontology and Graphs - toQuads and fromQuads for the advanced graph API

See also

• Bookstore domain - where all schemas are defined
• Schemas guide - schema registration and management