File Type/Signature Identifier
Identify a file's true type from its magic-byte signature, and flag it when the extension or reported MIME type disagrees.
About this tool
Every common file format starts with a short, fixed sequence of bytes called a "magic number" or signature — PNG images always start with the same 8 bytes, PDF documents always start with %PDF, and so on, regardless of what the file is named. This tool reads just the first 16–32 bytes of each file you choose and compares them against a table of well-known signatures, rather than trusting the file's extension or the MIME type your browser guesses from that extension — both of which can be wrong or deliberately misleading, for example a renamed file or an email attachment with a disguised extension. When the detected signature doesn't match the reported extension, a clear "Mismatch" flag is shown so you can spot it at a glance. Some formats, including Microsoft Office's modern formats (.docx, .xlsx, .pptx) and plain .zip archives, all share the same outer ZIP signature, so this tool reports those as "ZIP-based format" rather than guessing further; telling them apart exactly would mean looking inside the archive at its internal folder structure, which is outside what a quick byte-signature check can do. Nothing is uploaded anywhere; the bytes are read and compared entirely on your device.