File Type Identifier
Identify the real format of any file from its magic bytes — MIME type, extension and mismatch warnings.
Drag & drop any files here, or click to browse
No uploads. Only the first bytes are read, on your device.
How it works
Every file format starts with a fingerprint — a short run of "magic bytes" at the very
beginning of the file. A PNG always begins with 89 50 4E 47, a PDF with
%PDF-, a ZIP (and everything built on ZIP, like .docx or
.epub) with PK. This tool reads only the first 64 KB of each file
you drop, matches those bytes against a built-in table of about 60 signatures, and tells you
what the file really is — its true format, MIME type and canonical extension.
Because the check ignores the filename, it catches renamed and mislabelled files: a
screenshot saved as .txt, a JPEG with a .png extension, or a
download with no extension at all. Files whose bytes match no known binary signature are
tested as text, so JSON, XML, SVG, HTML, CSV, PEM keys and plain text are recognised too,
including any byte order mark. Everything runs in your browser with the File API — nothing
is uploaded, so it is safe for confidential documents.
Frequently asked questions
How does the tool know the file type without trusting the extension?
It reads the first bytes of the file — the "magic bytes" or file signature that almost every format starts with. A PNG always begins with 89 50 4E 47, a PDF with %PDF-, a ZIP (and .docx, .xlsx, .epub built on it) with PK. Those bytes are matched against a built-in table of around 60 signatures, so a renamed file is still identified correctly. Files with no known binary signature are sniffed as text, which catches JSON, XML, SVG, HTML, CSV, PEM keys and plain text.
Are my files uploaded anywhere?
No. Only the first 64 KB of each file is read, and it is read locally with the browser's File API. Nothing is sent to a server, there is no account and no tracking of file contents, so the tool is safe to use on confidential documents. You can even disconnect from the internet after the page has loaded and it keeps working.
What does an "extension mismatch" warning mean?
It means the filename promises one format but the bytes say another — for example a screenshot saved as notes.txt, or a JPEG named photo.png. That is usually harmless (someone renamed the file) but it can also indicate a corrupted download or a disguised file, so the tool shows the detected format and the extension it would normally use.