# SDKInitOptions.workerUrl

Part of [Initialization](https://kernstra.com/docs/web-sdk/config/init) in the Kernstra Web SDK 1.0.0 configuration reference.

- Type: `string`
- Page: https://kernstra.com/docs/web-sdk/config/init/workerurl

URL to `render.worker.js`, the prebuilt, self-contained worker bundle the package ships at `dist/render.worker.js` and exposes via the `./render-worker` export subpath. It is an ES module and must be served as a same-origin URL — Web Workers cannot be loaded from bare package specifiers at runtime. Either copy it to your static assets (works with every bundler) or, in Vite, import it with the `?url` suffix. The worker takes the engine's bytes from the page and makes no request of its own. Unlike `engineUrl`, it is not a self-hosting option: any license may set it, since the file is your own copy of one the package ships.

When a `workerUrl` is provided, page rendering moves off the main thread with no viewer configuration change; [`performance.workerEnabled: false`](https://kernstra.com/docs/web-sdk/config/performance/workerenabled) disables it. The worker renders from a copy of the document: under a production license that includes `export` with clean output it holds the document as edited; under any other license it holds only the bytes you handed over and is stopped at the first change to the document, after which every page renders on the main thread (see [Web worker rendering](https://kernstra.com/docs/web-sdk/guides/worker)). Without a `workerUrl` the worker is never created. Enabling it keeps the engine (~4.4 MB) in memory twice, once on each thread, though it is downloaded only once; the worker also holds its own copy of the document. See [Web worker rendering](https://kernstra.com/docs/web-sdk/guides/worker).

```ts
// Option B: Vite ?url import (Vite emits the file and returns its URL)
import RenderWorkerUrl from '@kernstra/pdf-web-sdk/render-worker?url';

await Kernstra.init({
  license: import.meta.env.KERNSTRA_LICENSE,
  workerUrl: RenderWorkerUrl,
});

// Option A: copy dist/render.worker.js to your static assets instead
// cp node_modules/@kernstra/pdf-web-sdk/dist/render.worker.js public/assets/render.worker.js
// await Kernstra.init({ license: import.meta.env.KERNSTRA_LICENSE, workerUrl: '/assets/render.worker.js' });
```

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