File Signature Detector
Identify a file's true type from its magic number — the distinctive leading bytes that every format writes at a known offset — rather than trusting the (easily forged) file extension. Drop a file or paste its leading bytes as hex; the tool reads only the first kilobyte locally and matches it against common signatures. Nothing is uploaded — the file never leaves your browser.
From a file
From hex bytes
A file's magic number is a fixed byte sequence a format writes at a known offset (usually the start), so the operating system and applications can identify the type regardless of the extension. This tool compares the leading bytes of your input against a built-in table of ~30 common signatures (images, archives, documents, audio/video, executables). It reads only the first 1 KB of any dropped file (enough to cover every signature, the furthest being the ustar marker at byte 257 of a tar archive). Some formats share a container — WAV and WebP both begin with RIFF, and MP4/M4A/HEIC/AVIF all carry an ftyp box at byte 4 — so the detector also checks the distinguishing brand at byte 8. It cannot identify plain-text formats (JSON, CSV, source code) by content alone, since they have no magic bytes. Pairs with the MIME-type lookup (extension-based) and hex viewer. Everything runs locally — nothing leaves your browser.