Why not just trust the extension?
The extension is metadata anyone can change. Renaming a file does not alter its contents, which is exactly how mislabelled and malicious files get opened.
All free toolsDeveloper tool · 100% free
MIME Type Detector
Identify a file's real type from its content signature rather than trusting the extension. A file named report.pdf can be anything at all, and the extension is the least reliable thing about it. It is free, needs no account, and adds no watermark to your result.
Built for: mime type detector
Deleted as soon as you download itFree · fair-use only
Drop file files hereJSON output · up to 100 files
Included in this tool
Magic-byte detectionExtension comparisonMIME guessJSON output
When you need this
What people use it for.
Checking what an unexpected attachment actually is before opening it
Identifying a file whose extension is missing or wrong
Verifying uploads in a workflow where the extension cannot be trusted
How it works
What happens to your file.
The leading bytes are matched against known format signatures, and where the format is parsable the structure is inspected to confirm, then compared against what the extension claims.
What this tool includes
Everything you need, without a paywall.
Magic-byte detection
Extension comparison
MIME guess
JSON output
Questions
Common questions.
What does a mismatch mean?
The content does not match the claimed type. Sometimes that is a harmless rename, such as a JPEG saved as .png. Sometimes it is deliberate disguise.
Can it identify any file type?
It recognises common document, image, archive and media formats by signature. Unknown or proprietary formats are reported as generic binary data.
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