How does the Finder know the right app to open a file with? Or QuickLook how to preview its contents? Or other services like Spotlight know how to index and handle files? UTIs.
UTI
In Big Sur and Monterey, if you’ve not opened an app’s Help book, the first time you do it may appear empty, or simply not work. Here’s why and how to fix it.
Many think that a file’s type is determined by its extension. Although partly true, that’s indirect: it’s the UTI which sets the type, as explained here.
Explaining inodes, names, dates, permissions, file types, and specialised attributes used for iCloud.
Explore UTIs, MIME and file types, extensions, and more. Now runs native on Intel and Apple Silicon Macs.
How these fundamental features work in macOS, using the pboard daemon and UTIs. With full log transcripts too.
An explanation of the magic which takes place when you double-click a document, the things that can go wrong, and how to fix them.
You’re checking through old files. How can you tell which file type they are when you don’t recognise the extension, or they don’t even have that to help?
What’s a UUID, and a UTI? What can you learn from each, and where can you look them up? Important info about these, and a new release of a tool to help.
Icons are a fundamental part of a graphical interface, and convey valuable information. Although QuickLook thumbnails can enhance, they can also conflict unless carefully thought out.
The Eclectic Light Company 