logohsb.horse

File Extension, MIME, and Signature Mismatch Checker

Compare a filename extension, the browser-declared MIME type, and leading file signatures locally to find format mismatches.

When an image or attachment opens only in some environments, this checker shows whether its name and contents agree. It reads at most the first 64 KiB rather than the whole file.

The selected file is not uploaded. Detection runs only in this browser.

File to inspect

Supports JPEG, PNG, GIF, WebP, AVIF, PDF, ZIP, GZIP, MP3, WAV, MP4, and WebM.

Diagnostic result

Choose a file to inspect.

    How to use it

    1. 1

      Choose a file

      Select one file whose name or MIME type may be incorrect.

    2. 2

      Compare three clues

      Review the extension, declared MIME, and format detected from the signature.

    3. 3

      Investigate a mismatch

      Check the original source or generation process instead of blindly renaming the file.

    Detection scope

    Polyglot files, damaged containers, formats inside ZIP files, and unsupported signatures cannot be fully identified. The result is an investigative clue, not proof of file identity.

    Frequently asked questions

    Will changing the extension fix every mismatch?
    No. The Content-Type or file generation process may also be wrong. Use the result as evidence while checking the source.
    Does unknown mean safe?
    No. It means no supported signature was identified and says nothing about safety or validity.
    Can this detect malware?
    No. This tool only checks format mismatches and is not a security scanner.