.NPY file signature
A Numpy Array file begins with the bytes 93 4E 55 4D 50 59 (.NUMPY 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 NPY file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 93 4E 55 4D 50 59Followed by major and minor version bytes and the header length. | .NUMPY |
MIME type: application/octet-stream · usual extensions: .npy
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.npy
file file.npyWindows (PowerShell):
Format-Hex -Path file.npy -Count 32If the bytes do not match
A file named .npy whose first bytes are something else is not a NPY 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 NPY guide explains what a genuine file should contain.