Got a file with no extension, a strange one, or a “photo” that will not open? Drop it here and the tool reads its first bytes, the “magic number” every format starts with, to tell you what it really is: JPEG or PNG, HEIC from an iPhone, PDF, DOCX or XLSX, ZIP, RAR or 7z, MP4, MP3, an Android app, a Windows program and dozens more. It tells you the right extension and warns you when a program is pretending to be a document.
loading toolHow to find out what type a file is
- Choose a file or drag it in (only its first 64 KB is read).
- Read its real type, the usual extension and the MIME type.
- If the name is wrong, rename the file with the suggested extension.
Good to know
- Plain-text formats like CSV, JSON and HTML have no magic number, so the tool reads the text itself to guess them.
- On Windows, turn on “File name extensions” in File Explorer’s View menu to see and change extensions.
Questions
How can it know the type without the extension?
Almost every format begins with a fixed pattern of bytes: PNG files start with 89 50 4E 47, PDFs with “%PDF-”, ZIP files with “PK”. The tool compares the start of your file with more than 50 such patterns, and looks inside ZIP files to tell DOCX, XLSX, EPUB and APK apart.
Why is a program pretending to be a PDF dangerous?
Scammers rename programs to look like invoices or photos. If you open one, it can install malware. If the tool says a “.pdf” or “.jpg” is really a program, do not open it.
Is my file uploaded?
No. The file is read by your own browser and never leaves your device, so it is safe to use with private documents. It also works offline once the page has loaded.
Is my data private?
Yes. Everything happens inside your own browser: nothing you type or choose is uploaded to us or anyone else.
Is it free?
Completely free, with no sign-up, no watermark and no limit on how many times you use it. Light ads keep the site running.
