Check what a file really is, not what its name says
Drop files to see their real type from their first bytes, and whether the name fits. Nothing is uploaded.
- Runs on your device
- No sign-up
- Works offline after a visit
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How to check what type a file really is
- Drop one or more files on the mat. Nothing is uploaded.
- Read the real type next to the name it has.
- Do not open a file marked Do not open until you know where it came from.
Questions
How does it know the type?
Most formats begin with a fixed run of bytes. A PNG starts with 89 50 4E 47, a PDF with %PDF. The checker reads the first 4 KB of each file and compares them with that list. It does not trust the name.
Why is a double extension dangerous?
Windows hides known extensions by default, so photo.jpg.exe looks like a photo. A file whose last part is a program type is flagged even when the first part looks harmless.
Can it prove a file is safe?
No. It tells you what the file is and whether its name fits it. A matching name does not make the content harmless, and an unknown type is not proof of danger.
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