# provideThumbnail(for:_:) Creates a thumbnail of a custom file type for a specific request. ``` func provideThumbnail(for request: QLFileThumbnailRequest, _ handler: @escaping (QLThumbnailReply?, (any Error)?) -> Void) ``` ## Parameters `request` The request that contains information about the thumbnail that you need to provide, such as the URL to the file. `handler` The completion handler to call when you finish creating a thumbnail. Call the completion handler with a [`QLThumbnailReply`](/documentation/QuickLookThumbnailing/QLThumbnailReply) if you can provide a thumbnail or with an if you can’t create a thumbnail. The platform doesn’t draw a thumbnail if you pass an `error` to the handler or the `reply` is `nil.` You can call the handler asynchronously after the method has returned. - `reply`: The object containing information about the thumbnail image that the platform uses to draw the thumbnail. - `error`: An error object that indicates why the thumbnail generation failed, or `nil` if the thumbnail generation succeeded. ## Discussion To provide a thumbnail for a custom file type, subclass [`QLThumbnailProvider`](/documentation/QuickLookThumbnailing/QLThumbnailProvider), implement this method, and return a [`QLThumbnailReply`](/documentation/QuickLookThumbnailing/QLThumbnailReply) that either contains a drawing block or the URL to an image file. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)