About this tool
The detector checks signature bytes first, then considers text patterns, extensions, and browser-reported MIME types. Results include the detection method and confidence level so you can understand their limits.
How to use
- Select or drag in the local files you want to check.
- Review the detected format, MIME type, method, signature bytes, and confidence level.
- Check whether the extension matches. Open the Hex File Viewer if you need to inspect the raw bytes.
Features
- Recognizes JPEG, PNG, GIF, WebP, BMP, PDF, ZIP, GZIP, RAR, and 7Z.
- Recognizes ELF, WASM, SQLite, ICO, WOFF, WOFF2, OTF, TTF, MP3, and MP4/MOV.
- Provides limited content-based estimates for text, JSON, XML, and similar files, clearly labeled as heuristic results.
- Shows the extension, browser-reported MIME type, and detection result separately. The extension alone is not treated as proof of the format.
How file signature detection works
- Typically reads only the first 64 KiB of a file, rather than loading an entire large file.
- Signature bytes are fixed markers near the start of some file formats. PNG and JPEG, for example, have different byte sequences that do not change when you rename an extension.
- Text formats without fixed signatures can only be estimated. A sample from a large file may not represent its entire contents.
- A ZIP signature is reported as ZIP or a ZIP-based format. It is not automatically classified as DOCX, XLSX, or PPTX.
- This tool identifies formats. It does not scan for viruses or determine whether a file is safe.
Limits
- Detection is limited to supported signatures and the sampled file header. Unknown, truncated, encrypted, or unusual formats may not be identified.
- An extension mismatch is a format-checking hint. It does not necessarily mean the file is damaged or unsafe.
Privacy
All files are processed only in your browser and are never uploaded to a server.
File names, entered text, and results are processed only in your current browser. Your input is not saved automatically. Download any results you want to keep before clearing the tool or leaving the page.
FAQ
How is the file type detected?
The tool checks signature bytes in the file header first. If no clear signature is found, it uses limited text and filename information and explains the basis for the result.
Can the extension differ from the actual format?
Yes. A JPEG renamed with a .png extension still contains JPEG data. The tool compares the detected format with the extension.
Is the MIME type always reliable?
No. Your browser may leave it blank or infer it from the extension. It is shown separately as reference information.
What are magic bytes?
They are fixed byte patterns used to identify certain file formats. Not every format has a reliable signature.
Can this tool detect viruses?
No. Format detection is not a security scan. This tool does not scan for viruses or declare files safe.