.MP3 file signature
A MPEG v1/2 Layer III audio file begins with the bytes 49 44 33 (ID3 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 MP3 file is still recognisable.
Known signatures
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 49 44 33An ID3v2 tag precedes the audio in most files. | ID3 |
| 0 | FF FBMPEG-1 Layer III frame sync without a tag. FF F3 and FF F2 also occur. |
MIME type: audio/mpeg · usual extensions: .mp3
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.mp3
file file.mp3Windows (PowerShell):
Format-Hex -Path file.mp3 -Count 32If the bytes do not match
A file named .mp3 whose first bytes are something else is not a MP3 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 MP3 guide explains what a genuine file should contain.