File Type Checker: Trust the Magic Bytes, Not the Extension
Renaming a file takes a second and changes nothing inside it. Magic bytes tell you what it really is.
What is the File Type Checker?
A file extension can be renamed in a second, but the opening bytes of a file, its magic signature, are much harder to fake by accident. This checker reads those first bytes in the browser and matches them against known signatures for PNG, JPEG, GIF, PDF, ZIP, and MP3 files. Everything happens locally, so the file itself is never uploaded for inspection.
How to use it
- Choose a file in the browser.
- Click Check File Type.
- Read the detected type from the magic bytes.
- Compare it with the extension to spot a renamed file.
Worked example
A file whose first bytes are 89 50 4E 47 is detected as a PNG image, whatever its name says.
How can I tell a real PNG from a renamed file?
Check its opening bytes. A genuine PNG starts with 89 50 4E 47, while a renamed document or archive starts with its own signature instead.
Frequently asked questions
Why check magic bytes instead of the extension?
Extensions are just part of a name and can be changed freely, while magic bytes describe what the file actually starts with.
What if the type comes back unknown?
It means the opening bytes did not match the six signatures this tool knows, not that the file is broken.