Drop your files
One with a missing, wrong or suspicious extension, or any file you're curious about.
File type detector
Drop a file and see what it actually is, read from the bytes at the start of the file rather than trusted from its name. Useful for a file with no extension, a mislabeled download, or checking before you open something unfamiliar.
- Free
- No sign-up
- Runs in your browser
100% private — files are read in your browser and never uploaded.
How it works
Read the detected type
Based on the file's own content, not its name.
Check for a mismatch
A warning appears if the extension doesn't match the content.
An extension is just a label; this looks inside
A file's extension, the letters after the dot, is nothing more than a hint the operating system trusts. Anyone, or any process, can rename "document.pdf" to "document.txt" without changing a single byte of the actual content, and many real files arrive with no extension at all after being downloaded from an unusual source. Most file formats, on the other hand, start with a fixed sequence of bytes called a signature or magic number that identifies them reliably, regardless of what the file is named. This tool reads that signature.
What it recognizes
Common image, audio, video, document, archive and font formats, identified by the bytes at the start of the file: PDF, PNG, JPEG, GIF, WebP, MP3, WAV, MP4, ZIP, RAR, 7-Zip, Gzip, TAR, SQLite databases, TrueType and OpenType fonts, and more. It also recognizes plain text when the start of a file looks like readable characters rather than any known binary format.
Looking inside ZIP-based Office files
Modern Word, Excel and PowerPoint files, along with OpenDocument files and EPUB books, are all ZIP archives internally with a particular internal folder structure. Rather than just reporting "ZIP archive" for all of them, this tool opens the archive and checks which internal folders are present to tell a .docx from an .xlsx from a .pptx, entirely in your browser.
Catching a mismatch
When the detected content does not match what the file's own extension implies, for example a file called "photo.jpg" that is actually a PNG or not an image at all, the tool flags the mismatch. That is worth a second look before opening the file, though a mismatch is not always a sign of anything malicious: browsers and export tools sometimes save a file in a related format under the wrong extension by accident.
Limits
Signature detection identifies the file format, not whether the file is safe to open; it does not scan for malware. Some formats do not have a distinctive signature and cannot be identified this way. The file is read only in your browser and never uploaded.
Frequently asked questions
How do I find out what type a file really is?
Drop it here. The tool reads the bytes at the start of the file, which identify the format regardless of the file's extension or name.
Can it tell if someone renamed a file's extension?
Yes, if the detected content does not match the extension, a mismatch warning appears.
Can it tell a Word document from an Excel file?
Yes. Both are ZIP archives internally, so the tool opens the archive and checks the internal folder structure to tell them apart.
What if the file has no extension at all?
The detector still works, since it reads the file's content rather than relying on its name.
Does this check if a file is safe to open?
No, it identifies the format only. It is not a virus scanner and does not guarantee a file is safe.
Is my file uploaded to check its type?
No. It is read entirely in your browser.
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