WeVividWeVividCheck a file's true type, size and metadata.
Files carry a 'magic number' — a few specific bytes at the very start that identify the format (for example, JPEGs always start with FF D8 FF). This tool reads only those first few bytes and matches them against known signatures, rather than trusting the file extension or the browser-reported MIME type, both of which can be wrong or spoofed.
This can happen if a file was renamed with the wrong extension, if it's a format this tool doesn't recognise yet, or — occasionally — if a file has been deliberately disguised. A mismatch is worth investigating before opening the file.
No — only the first 16 bytes are read locally in your browser to check the signature. The rest of the file is never read or sent anywhere.