File Type Detector - Check Real File Type

What does this file type detector do?

Drop any file and this tool reports what the file really is, judged from the bytes at the start of the file instead of the name. It reads the magic number (file signature), shows the detected extension and MIME type, displays the exact bytes it matched, and compares the result with the extension in the file name.

How does it work?

• Magic bytes — most formats start with a fixed byte sequence: PNG with 89 50 4E 47, PDF with %PDF-, ZIP archives with 50 4B 03 04.
• Container formats — RIFF (WAV, AVI, WebP) and ISO base media (ftyp: MP4, MOV, AVIF, HEIC) are told apart by a tag a few bytes further in; ZIP archives by the entry names inside.
• Deep reads — a few signatures live outside the first bytes: ISO 9660 images carry CD001 at offset 0x8001, and DMG images carry koly in their final 512 bytes. The tool reads exactly those small ranges.
• Header only — the file is never decoded or rendered, so the check is instant even for multi-gigabyte files.

Why the extension can lie

A file name is only a label: anyone can rename setup.exe to invoice.pdf, and download managers sometimes guess the extension from the server's Content-Type header. Checking the header bytes shows the real format before you open, share or upload the file.

Some mismatches are harmless: a truncated download, a hand-renamed file, or a container format reused for something else. The tool adds a note for those cases instead of raising a false alarm.

Supported formats

Around 70 signatures: images (JPEG, PNG, GIF, WebP, AVIF, HEIC, TIFF, BMP, ICO, PSD, XCF, JXL, DICOM), audio and video (MP3, AAC, FLAC, OGG, Opus, WAV, MIDI, MP4, MOV, MKV, WebM, AVI, FLV, ASF, MPEG-TS), archives (ZIP and its DOCX, XLSX, PPTX, EPUB, JAR, APK and ODT variants, GZIP, BZIP2, XZ, Zstandard, 7z, RAR, TAR, AR, DEB, CAB, RPM, ISO, DMG), documents (PDF, PostScript, RTF, MOBI, iCalendar, vCard, SQLite), binaries (ELF, PE, Mach-O, Java class, WebAssembly, Windows shortcut, SWF, pcap) and fonts (TTF, OTF, TTC, WOFF, WOFF2). Formats without a signature are reported as unknown.

Privacy and security

Everything runs in your browser: only the first bytes of the selected file are read through the File API, and no byte leaves your device. Nothing is uploaded and nothing is stored after you close the page.

FAQ

Does it open or parse the file?

No. It only compares header bytes against known signatures, so it is safe to check unknown or suspicious files — nothing is executed, decoded or rendered.

Why does a DOCX report a ZIP note?

DOCX, XLSX, PPTX, EPUB, JAR, APK and ODT are all ZIP archives. The tool reads the entry names inside the archive to name the right subtype and adds a note, because the first bytes alone cannot tell them apart.

Can a file pass the check and still be malicious?

Yes. A magic number is a hint, not a guarantee: a polyglot file can be valid in two formats at once, and a crafted file can carry the right header without being a valid document. Real upload validation belongs on the server.

Why is my file type unknown?

Only formats with a distinctive header can be recognized. Plain text, CSV, JSON, XML, SVG and many niche or proprietary formats have no fixed signature, so the tool reports that no known signature was found.