More Developer Tools

File Type Checker

Check a file’s likely type from its contents instead of trusting its filename alone. The checker reports signature evidence, MIME type, confidence, and whether the extension agrees.

Inspect a file

File signatures and magic bytes

Many binary formats begin with recognizable bytes such as PNG’s fixed header or PDF’s %PDF- marker. Other formats use containers: DOCX, XLSX, PPTX, EPUB, and JAR files are specialized ZIP archives whose internal paths reveal their purpose.

Some formats overlap or have no unique header. The confidence label distinguishes strong signature matches from text-based guesses, and the browser-reported MIME type is shown separately because it may rely on the filename.

Frequently asked questions

How does the File Type Checker identify a file?

It reads a small portion of the file and compares known header bytes, container markers, or text structure with common file-format signatures. ZIP-based Office and EPUB files may also be identified from internal filenames.

Can a file extension be wrong?

Yes. A filename can be renamed without changing its contents. This tool compares the extension with the detected signature and reports a mismatch when the evidence is clear.

Does identifying a file prove it is safe?

No. File identification is not antivirus scanning, malware analysis, or proof that content is trustworthy. Treat unexpected files cautiously even when their format is recognized.

Why might a file type be unknown?

The format may not have a distinctive signature, may be encrypted or damaged, or may not be included in this tool’s supported signatures. Plain text and source code are identified with lower-confidence heuristics.

Is the selected file uploaded?

No. Signature reading and archive inspection happen locally in your browser.

Related tools