.XZ file signature
A XZ compressed data file begins with the bytes FD 37 7A 58 5A 00 (.7zXZ. in ASCII) at the start of the file. The signature is the same whatever the file is named, which is why a renamed or extensionless XZ file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | FD 37 7A 58 5A 00 | .7zXZ. |
MIME type: application/x-xz · usual extensions: .xz
How to check a file's signature
Without installing anything: drop the file on our detector. It reads the bytes in your browser and shows the hex dump alongside the verdict; nothing is uploaded.
macOS and Linux (Terminal):
xxd -l 32 file.xz
file file.xzWindows (PowerShell):
Format-Hex -Path file.xz -Count 32If the bytes do not match
A file named .xz whose first bytes are something else is not a XZ file. The common explanations are a wrong or deliberately misleading extension, a download that saved an HTML error page instead of the file, or a container such as ZIP wrapping the real content. The detector reports what the bytes say; the XZ guide explains what a genuine file should contain.