.AI file signature
A Adobe Illustrator Artwork file begins with the bytes 25 50 44 46 2D (%PDF- 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 AI file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 25 50 44 46 2DModern Illustrator files are PDF-compatible. Very old ones begin %!PS-Adobe. | %PDF- |
MIME type: application/postscript · usual extensions: .ai
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.ai
file file.aiWindows (PowerShell):
Format-Hex -Path file.ai -Count 32If the bytes do not match
A file named .ai whose first bytes are something else is not a AI 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 AI guide explains what a genuine file should contain.