Adinand Auto File Sorter

What format does Android use?

Last reviewed: September 22, 2026 · Markdown version

"Format" means two unrelated things here, and the answer you need depends on which one you are asking. One is the filesystem the storage is formatted with. The other is which kinds of file the phone can open. Both are worth a paragraph; only the second affects how you organise anything.

The filesystem

Android's own platform documentation is specific about storage that gets absorbed into the device. From the adoptable storage page (read 22 September 2026): "Adopted devices must be formatted with a filesystem that supports POSIX permissions and extended attributes, such as ext4 or f2fs." Those are the same kinds of filesystem the internal storage uses.

Two consequences that matter in practice. Adopted storage is encrypted to the phone it was adopted by, and Android states the result plainly: "the encryption keys should not be extractable from the parent device, and therefore the storage device can't be mounted elsewhere." So a memory card set up as internal storage is not readable in a computer or another phone. A card left as portable storage is the opposite — meant to be moved between machines — which is why that choice at setup matters more than it looks.

The file types

This is almost certainly the real question, and the answer is that Android does not have a list of blessed formats. It opens whatever an installed app claims it can open, and identifies files by their extension and declared type. Which means the useful fact is about you, not the phone: the extension on the end of a file name is what decides which app opens it, what a file manager shows it as, and what any sorting tool can do with it.

That is why a file with no extension at all is awkward on Android. Nothing knows what it is, no app offers to open it, and a file manager shows it as a generic item.

Where the folder structure comes in

Android's storage model is the third thing people mean by "format" — where files are allowed to live. Shared media and documents sit in public folders; an app's own data does not, and cannot be browsed by other apps. That separation is why "I can see it in this app but not that one" is a normal answer rather than a fault. Scoped storage, explained.

What this means for keeping a phone tidy

You cannot usefully organise by filesystem, and you do not need to. The organisable property is the extension — it is stable, it is visible, and it is what every tool on the phone already keys on. A .pdf is a document whenever it arrived; a folder built on that stays meaningful for years, which is not true of a folder built on dates.

Where Adinand Auto File Sorter fits

It sorts by extension, and nothing else. It watches a folder — Downloads by default — and moves what lands there into Downloads › Sorted Files under one of seven categories, using these exact extension lists:

A file with no extension is never sorted, and the app does not read what is inside a file to decide where it goes. On Pro you can add your own rules — an extension list, or a keyword the file name must contain — which is how a category list becomes yours. Android 10 and later, Android only.

Related: What is scoped storage? · Seeing all files on Android · Where documents are stored · Sorting by type and date