File Type Detector
Compare file magic bytes, filename extension, browser MIME, and text-content hints locally
Signature detection reads at most the first 10 MB. The file is never uploaded, executed, or opened as active content.
The file signature, extension, and MIME comparison will appear here.
About this tool
Inspect a local file of up to 100 MB. The tool reads at most its first 10 MB and compares recognized binary signatures, filename extension, browser-provided MIME, and a text-content hint. It reports the first 32 bytes in hexadecimal and individual consistency checks. These signals can be related: browser MIME often comes from the filename. Signature recognition identifies a format family; it does not validate the complete structure, scan for malware, or render the file.
Scenario Recipes
Read the built-in extension mismatch example
Goal: See why a filename and browser MIME can agree while the bytes suggest another format.
- Choose Try example to inspect the synthetic renamed-photo.jpg sample.
- Compare its PNG signature with the .jpg filename and image/jpeg browser MIME.
- Read the mismatch messages or copy the report.
Result: This sample contains a PNG-like header for signature testing; it is not a complete, renderable PNG. Recognizing a signature does not validate an entire file.
Failure Clinic (Common Pitfalls)
Unknown signature does not mean invalid file
Cause: Some formats have no binary signature, and inspection is limited to the first 10 MB. Text hints examine at most the first 64 KB.
Fix: Read the text hint and other reported evidence. A hint such as CSV-like text is a heuristic, not CSV parsing or format validation.
Several matching labels are not independent confirmations
Cause: Browser MIME is often inferred from the filename. A missing MIME is reported as missing, and MIME aliases may produce differences without corruption.
Fix: Interpret each comparison separately. βNo known conflictβ does not mean all evidence is present or that the file is safe or complete.
Frequently Asked Questions
Why can a renamed file produce a mismatch?
Renaming changes the filename but not its bytes. A PNG-like signature can therefore disagree with a .jpg name and an image/jpeg MIME inferred by the browser.
How much data is inspected?
Files up to 100 MB are accepted. Signature detection reads at most the first 10 MB; text hints sample at most 64 KB. Formats requiring more data can remain unrecognized.
Is the file uploaded?
No. File reading, signature comparison, and report generation run locally in the browser.
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