.ZLIB file signature
A zlib compressed data file begins with the bytes 78 9C at the start of the file. The signature is the same whatever the file is named, which is why a renamed or extensionless ZLIBSTREAM file is still recognisable.
Known signatures
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 78 9CDefault compression. | |
| 0 | 78 01No or low compression. | |
| 0 | 78 DABest compression. |
MIME type: application/zlib · usual extensions: .zlib
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.zlib
file file.zlibWindows (PowerShell):
Format-Hex -Path file.zlib -Count 32If the bytes do not match
A file named .zlib whose first bytes are something else is not a ZLIBSTREAM 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 ZLIBSTREAM guide explains what a genuine file should contain.