.DWG file signature
A Autocad Drawing file begins with the bytes 41 43 31 30 (AC10 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 DWG file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 41 43 31 30Followed by two digits giving the version: AC1032 is AutoCAD 2018 and later. | AC10 |
MIME type: image/vnd.dwg · usual extensions: .dwg
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.dwg
file file.dwgWindows (PowerShell):
Format-Hex -Path file.dwg -Count 32If the bytes do not match
A file named .dwg whose first bytes are something else is not a DWG 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 DWG guide explains what a genuine file should contain.