.GZ file signature
A gzip compressed data file begins with the bytes 1F 8B at the start of the file. The signature is the same whatever the file is named, which is why a renamed or extensionless GZIP file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 1F 8BThe third byte is the compression method, almost always 08 (deflate). |
MIME type: application/gzip · usual extensions: .gz
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.gz
file file.gzWindows (PowerShell):
Format-Hex -Path file.gz -Count 32If the bytes do not match
A file named .gz whose first bytes are something else is not a GZIP 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 GZIP guide explains what a genuine file should contain.