Apple’s assets.car format decoded – access to in-app graphics and controls | News

Anyone who has already had some experience with macOS often knows that an app’s structure is just a folder whose contents are not displayed by the Finder by default. If you open the context menu with a secondary click and select “Show package contents,” the macOS file manager shows itself graciously and reveals the internal folder structure. For example, the app icon can be found under “Contents/Resources” (for macOS 15 and earlier). In this folder there is also an archive file called “Assets.car” in every app. Their content was previously unclear. A developer with the pseudonym “Ordinal0” now explains in a detailed blog post how he decrypted the proprietary .car format.

Xcode usually creates the Assets.car file independently; This contains graphics for app-specific controls, special mouse cursor graphics and the like. Developers can interact with “asset catalogs,” as Apple calls these files, using two command-line tools: “actool” creates these files, and “assetutil” allows some further interaction with these archives. Using a hex editor and disassembler, Ordinal0 extracted the secrets from the file format and the system components piece by piece. Basically, Apple apparently uses an ASCII format called BOM (Bill of Materials) as a general file structure. The individual media that are hidden in the document then follow a strict nomenclature.

What was hidden in the Assets.car file was previously difficult to decipher.

Try it out in the browser
It was apparently not enough for the developer to document his findings and the procedure in detail. He also embedded an interactive demonstration into his website. If you drag an Assets.car file from any app onto the designated area, the applet will show its table of contents after a short while. After clicking on the “Assets” tab, an overview of the media contained appears. When we tested asset catalogs from Apple apps, we discovered collections of controls, such as scroll bars or toolbar buttons. SVG files, which form the basis of Liquid Glass icons, also appeared here. However, the demo didn’t turn out to be particularly stable – the browser tab often crashed before we could extract individual graphics. The developer freely admits this – his hope is that software developers will feel called upon to develop independent programs for browsing car files.

Automator’s Assets.car file contains graphics and vector files – the latter apparently being the individual elements of the Liquid Glass icon.