File Signature Viewer
Identify a file's true type from its signature bytes.
What a file really is
Files begin with distinctive bytes, called a file signature or magic number, that identify their true type regardless of the filename. This reads a file's signature to identify what it actually is, in your browser, so the file stays on your device.
Load a file to identify it from its signature.
Why the signature beats the extension
This gets at a genuinely important idea: a file's real type is defined by its contents, not its name. The extension after the dot is just part of the filename and can be anything — renamed, missing, or deliberately wrong — whereas the signature, the specific bytes at the start of the file, is put there by whatever created the file and reliably marks its actual format. Many file types have a recognisable signature, so reading those opening bytes reveals what a file truly is even if its extension lies. This matters for security, since disguising a file's type by changing its extension is a classic trick, and for practicality, when a file has no extension or the wrong one and will not open. Identifying the real type lets you handle a file correctly. Doing it in the browser means even a suspicious or sensitive file is examined locally without uploading, so you can safely identify what something really is on your own device rather than trusting its name or an online service.
File Signature Viewer FAQ
What is a file signature?
Distinctive bytes at the start of a file, also called a magic number, put there by whatever created it, that identify its true type regardless of the filename.
Why is the signature more reliable than the extension?
Because the extension is just part of the name and can be renamed or wrong, while the signature is set by the file's creator and marks its actual format.
Is my file uploaded?
No. The identification happens in your browser, so the file stays on your device.