File Inspector
Check file metadata.
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How a file's real type is identified
A file extension is only a label, and anyone can change it. What actually identifies a file is its magic number: a short signature at the start of the data. A PNG begins with the bytes 89 50 4E 47, a PDF with %PDF-, a ZIP with PK, and a JPEG with FF D8 FF. Inspecting those bytes tells you what a file genuinely is, regardless of what it is called.
Beyond the signature, an inspector reports the exact byte size, and often a hash such as SHA-256 — a fingerprint that lets you verify a download matches what the publisher intended, or confirm two files are identical without comparing them by eye. Many formats also carry internal metadata: creation dates, producing software, dimensions, and codecs, all of which say something about where a file came from.
Why we built this tool
You inspect a file when something does not add up: a download that will not open, an attachment with a suspicious name, an unfamiliar extension, or two copies of a document where you need to know whether they are truly the same.
That last case is a security question, and mismatched extensions are a classic malware technique. Uploading a suspect file to an inspection service is a poor idea for privacy reasons and pointless for speed reasons, since reading a signature takes microseconds. Ours reads the bytes in your browser with the File API, so nothing is transmitted and nothing is stored — and it works on files of any size, since only the header and a hash pass need reading.
Tips and common mistakes
- A mismatch between the extension and the detected type is a warning sign, especially on an email attachment.
- Compare a published SHA-256 hash against your download before installing anything.
- Zero-byte files are usually the result of a failed transfer rather than a corrupt source.
- The detected type comes from the file's own signature, which is far more reliable than its name.
Quick start: using File Inspector
- Load the file you want to identify.
- Read the detected type and compare it with the file's extension.
- Treat any mismatch as a warning sign, particularly on an emailed attachment.
- Check the size and hash if you are verifying a download against a published value.
- Review any metadata the tool reports about the file's origin.
For photographs specifically, Extract EXIF reads far more detail; for archives, ZIP Extractor lists the contents.