Find out what a file really is – from its first bytes, not from its name. Useful for files without an extension or with the wrong one. Your files stay on this device: they are read here in the browser and never uploaded.
Drop files or folders here
as many as you like – only the first few KB of each file are read
No file matches this filter.
How does it work?
Most file formats start with a fixed "signature" (magic bytes): a PNG picture with 89 50 4E 47,
a PDF with %PDF-, a ZIP archive with PK. The tool reads the first 64 KB and the last
64 KB of each file and compares them with a list of signatures. Containers are looked into: a ZIP is told apart
from a Word document, an Android app or an e-book by the names inside it, old Office files by the streams inside
them, MP4/MOV/HEIC by their brand, WAV/AVI/WebP by their RIFF type and an MP3 by the audio after its ID3 tag.
Signature match means the format's signature or structure was found. Guess means there is no signature (text files, some old formats) and the type comes from the content. Unknown files show their first bytes so you can look yourself.
"Download" saves a copy of the same file under the new name – the copy is made in your browser. A wrong extension is replaced, otherwise the new one is added.