> ## Documentation Index
> Fetch the complete documentation index at: https://ddp.drawdy.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Webview API

> The `acquireDrawdyApi()` global available inside a webview document.

Inside a webview document, Drawdy injects a global `acquireDrawdyApi()`. Acquire it once; messages you post reach the owning driver as [`subscription:webview:message`](/protocol/subscriptions#webview-events) events.

```ts theme={"system"}
type DrawdyWebviewApi = {
    postMessage(message: unknown, transfer?: Transferable[]): void;
    onMessage(listener: (message: unknown) => void): () => void;
};
```

* **`postMessage`** sends a driver-defined message. It is buffered until the host connects, so it is safe to call immediately. Large payloads (`ArrayBuffer`, `ImageBitmap`, …) referenced inside `message` can be listed in `transfer` to move rather than copy them; they are re-transferred at every relay hop.
* **`onMessage`** listens for messages the driver sends via [`command:webview:post-message`](/protocol/commands#webviews). It returns a dispose function.