If a file's magic bytes are wrong, missing, or overwritten, this tells you what they should be — and can patch a repaired copy for download. Useful after a bad transfer, a hex-editing mistake, or an extension that was changed by hand.
If you're here because something threw one of these, this tool shows you exactly what's wrong and how much is recoverable:
Only patches the magic-byte header — it can't fix truncation, missing footers/trailers, or damage elsewhere in the file, and it doesn't recompute per-format internal checksums (e.g. a PNG chunk CRC) beyond the header bytes themselves. Detection is limited to the signature database this site ships with; a format that isn't recognized can't be auto-selected, though you can still pick one manually. Only the first 64KB of the file is read for detection — enough for every known header — but the whole file is read and rewritten when you download the repaired copy. No batch mode — one file at a time.