.ZIP file signature
A Zip archive data file begins with the bytes 50 4B 03 04 (PK.. 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 ZIP file is still recognisable.
Known signatures
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 50 4B 03 04Local file header; the common case. | PK.. |
| 0 | 50 4B 05 06Empty archive (end-of-central-directory only). | PK.. |
| 0 | 50 4B 07 08Spanned (multi-volume) archive. | PK.. |
MIME type: application/zip · usual extensions: .zip
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.zip
file file.zipWindows (PowerShell):
Format-Hex -Path file.zip -Count 32If the bytes do not match
A file named .zip whose first bytes are something else is not a ZIP 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 ZIP guide explains what a genuine file should contain.