File Structure Pre-Check
A quick, private health scan for any file — no upload, nothing sent to a server.
File Structure Pre-Check
Scan a file’s header and tail to catch corruption, truncation, or a wrong extension — before you waste time trying to open it.
Report
The pre-check report appears here.
When to use this
Reach for this when a file “won’t open” and you don’t know why. Common triggers: a download that stopped halfway, a file you renamed years ago and forgot the real type, a USB drive pulled out mid-copy, or an archive that errors the moment you extract it. The pre-check tells you whether the bytes look structurally sound before you hand the file to another app.
Worked example
A coworker sends report.final with no extension. You drop it in: the header reads 25 50 44 46 (the PDF signature), so the tool reports “Detected format: PDF” and suggests renaming to .pdf. One rename later, it opens. In a second case, a .zip shows the PK header but no end-of-directory record — the tool flags it as truncated, so you re-download instead of fighting a corrupt archive.
What it can and can’t tell you
It checks signatures and container structure, not pixel- or content-level damage. A file can pass the pre-check and still contain a bad sector or logical corruption inside. It also can’t repair anything — it is a diagnostic. For archives and PDFs it specifically looks for the end-of-file markers those formats require, which is the fastest way to spot a truncated download.
FAQ
Does it upload my file? No. Every check runs on your device; the bytes never leave the browser tab.
Why does it say “no recognizable signature” for a text file? Plain text, CSV, and many log files have no magic bytes. That is normal — it just means signature scanning can’t classify them, not that they are broken.
Can it fix the file? No. It points you at the likely problem (wrong extension, truncation) so you can rename or re-download. Pair it with the File Info tool to confirm size and type first.