# Kernstra.init()

```ts
static init(options?: SDKInitOptions): Promise<void>
```

Initialize the SDK — verifies the license and loads the engine binary. Call before creating any viewer; resolves when the engine is ready.

Idempotent: a second call with the same options gets the same promise (React's StrictMode needs no guard), one with other options rejects with `INVALID_ARGUMENT`, and a failed call starts over on the next. An empty or missing `license` means "no license given"; only `setLicense('')` signs out and forgets the cached token.

The token is verified locally in milliseconds; its status is confirmed with the licensing API once per load. A load that holds a recent good answer never waits; a load without one (the first on a browser, site data cleared, a frame without storage, an answer older than 48 hours, or a paused license) waits for the check, at most 8 seconds. Nothing runs that we did not publish: the engine, the shaping and subsetting binaries and every bundled font are downloaded from the asset store your license names, by digest, verified and cached in the browser.

- Kind: static method
- Since: 1.0.0

| Parameter | Type | Description |
| --- | --- | --- |
| `options?` | `SDKInitOptions` | `license` (your license token), `engineUrl`, `shaperUrl` and `subsetterUrl` (self-hosted copies of the binaries — self-hosting licenses only), `workerUrl` (the render worker), `styleNonce` (the page's CSP nonce, carried by every stylesheet the SDK injects) and `licensePopup` (the "License required" popup in your own words). See [Initialization](https://kernstra.com/docs/web-sdk/config/init). |

Returns `Promise<void>`: Resolves when the engine is ready.

Throws:

- `LICENSE_REQUIRED` — no valid license, or not a secure context (the SDK runs only over HTTPS or on `localhost`; on a plain-HTTP origin it refuses to start with reason `insecure-context`).
- `FEATURE_NOT_LICENSED` — `engineUrl`, `shaperUrl` or `subsetterUrl` given without a self-hosting license.
- `ENGINE_LOAD_FAILED` — the binary was not downloaded, not verified, or not started.
- `INVALID_ARGUMENT` — a second call with other options, a `styleNonce` that is not base64 or base64url, or a `licensePopup` part that is not a string.
- `INVALID_STATE` — called outside a browser, where there is no `window` or `document`: server rendering.

```ts
await Kernstra.init({ license: import.meta.env.KERNSTRA_LICENSE });
```

Part of [Kernstra](https://kernstra.com/docs/web-sdk/api/kernstra) in the Kernstra Web SDK 1.0.0 API reference.

Web page: https://kernstra.com/docs/web-sdk/api/kernstra/init