---
title: "Call aontu from TypeScript"
description: "Embed the engine in Node with the `Aontu` class: parse, unify and generate from your own code."
source: "https://aontu.dev/how-to/call-from-typescript/"
---

# Call aontu from TypeScript

Embed the engine in Node with the \`Aontu\` class: parse, unify and generate from your own code.

Rendered from [`docs/how-to/call-from-typescript.md`](https://github.com/aontu-lang/aontu/blob/main/docs/how-to/call-from-typescript.md) in the engine repository, where a correction belongs, and where the test suite executes every example on this page.

The npm package `aontu` is not a wrapper around the CLI: the CLI is a thin client over the class the package exports. Requires Node ≥ 22. Three methods cover most embeddings:

```ts
import { Aontu } from 'aontu'

const aontu = new Aontu()

aontu.generate('a: 1 b: $.a')   // { a: 1, b: 1 }   (a plain JS value)
aontu.unify('a: *1 | number')   // a Val; .canon is '{"a":*1|number}'
aontu.parse('a: number')        // a Val AST, not yet unified
```

`generate` throws an `AontuError` on a conflict, or when the result is not fully concrete: a schema is a valid document but not a generable one. When you want to see an unresolved or schema-bearing result rather than a final value, take `unify(...).canon` ([see the canonical form](https://aontu.dev/how-to/see-canonical-form)); when you want every problem instead of the first throw, [collect errors](https://aontu.dev/how-to/collect-errors).

Two habits keep an embedding correct. Serialise generated output with the package’s `exactJSON`, never `JSON.stringify`: a document using `0d` exact literals generates `bigint` and `Decimal` values that `JSON.stringify` refuses to write ([exact numbers](https://aontu.dev/docs/reference-api#exact-numbers-and-exactjson)). And treat a parsed `Val` tree as single-use: unification refines it in place, so parse again for every independent evaluation ([evaluation consumes the tree](https://aontu.dev/docs/reference-api#evaluation-consumes-the-tree)). The string entry points parse per call and are always safe.

The full surface (options, contexts, the `Val` classes, and the library forms of the CLI verbs: `vet`, `get`, `why`, `subsume`, …) is the [TypeScript API reference](https://aontu.dev/docs/reference-api#typescript-api). To parameterise a model from code, [inject host values](https://aontu.dev/how-to/inject-host-values); for the Go port, [call aontu from Go](https://aontu.dev/how-to/call-from-go).