AR File Format (.ar)
An AR file is a Unix archive that concatenates one or more files behind a short per-file header, the format compilers use for static library .a files and that dpkg uses as the outer wrapper of a .deb package.
AR at a glance#
| Full name | Unix archiver |
|---|---|
| File extension | .ar |
| Category | Archives |
| Developer | Ken Thompson and Dennis Ritchie (AT&T Bell Laboratories) |
| First released | 1971 |
| MIME types | application/x-archive |
| Other extensions | .a |
| Compression | Uncompressed |
| FileFlip support | FileFlip reads this format but does not write it |
What a .ar file can hold#
These are the things a AR file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Streaming | Yes |
|---|
Strengths and limitations of AR#
What AR does well
- Header and layout have stayed essentially unchanged since 1971, so old and new ar implementations still read each other's output
- Fixed 60-byte per-file header is smaller than tar's, which matters when an archive holds many small object files
- Its role as the outer layer of a .deb never changed, so any ar-aware tool can pull a Debian package apart without dpkg
Where AR falls short
- No directory structure at all, just a flat list of files, so it cannot represent a folder hierarchy
- No compression, and filenames longer than the classic 16-byte field need a format extension (GNU or BSD) that not every tool agrees on
- Never formally standardized as a single specification, so BSD, GNU and Windows variants differ in the details
Reach for ar when linking a static library, where the .a file it produces is what the linker expects, or when inspecting the outer layer of a .deb package.
Convert an AR archive to tar or zip when the files inside need to be handled by tools that do not know the static-library-oriented ar format.
How to open a .ar file#
A .ar file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts AR into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | 7-Zip |
| macOS | ar (command line) |
| Linux | ar (binutils), 7-Zip (p7zip) |
| Web | FileFlip |
AR questions people ask#
What is an AR file used for today?
An AR file's two remaining jobs are holding compiled object files as a static library, with the .a extension, and serving as the outer wrapper of a Debian .deb package. Almost nothing else uses the format anymore.
How is an AR archive different from a TAR archive?
Both concatenate files with a header in front of each, but an AR archive has no directory structure and a much smaller fixed header, since it was built for flat collections like object files rather than whole folder trees. Tar became the general-purpose choice while ar stayed specialized.
Why does a .deb package use the ar format?
Debian's package format wraps three items, a version marker and two tarballs, in an ar archive because ar's layout is simple enough to parse without any real library, which keeps tools like dpkg lightweight and lets any ar-aware program open a .deb without understanding Debian packaging at all.
Converting AR files#
Convert AR to another format
FileFlip does not write .ar files, so nothing on the site converts into this format. It works as a source only.
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.