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File Signature Checker — Identify a File by Its Magic Number
Upload a file to read its magic number — the first few bytes that identify true file type regardless of what the extension claims — which catches a file that has been renamed with the wrong extension, or confirms what an extensionless file actually is, entirely in your browser.
How to use File Signature
- Upload the file.
- Read the detected file type from its byte signature.
- Compare against the file's claimed extension.
Frequently asked questions
- Why check the magic number instead of trusting the extension?
- A file extension is just a label anyone can change; the magic number is the file's actual leading bytes, so it reveals the true format even if the extension was altered, deliberately or by accident.
- Is my file uploaded to a server?
- No. Only the first bytes are read locally in your browser to identify the signature — the file is never transmitted.
- What if the file has no recognized signature?
- Some formats (plain text, some legacy formats) have no distinct magic number, so it may report as unrecognized rather than a false positive.
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