JA Tool

FileType Sniffer: Guide

Detect the real file format from its magic number (signature), not the extension.

What it does

Reads magic numbers / file signatures to guess the real format
Helps spot extension spoofing (e.g., “.jpg” that isn’t a JPEG)
Useful to identify unknown or partially broken files
Browser-only, no storage

Open the tool 日本語ガイド

Use this when

You suspect the extension doesn’t match the content
A file won’t open and you want to know what it is
You want a quick first-pass check on received files

Keywords: magic number, file signature, file type detector, extension spoofing

How to use

Open the tool
Select a file (or drag & drop)
Read the detected format and shown signature

Tip: if the detected type is different, renaming the extension may help (at your own risk).

Notes (limits)

Detection is best-effort; complex/encrypted/corrupted files can be misdetected.
This tool does not guarantee malware safety.
It may not inspect contents inside archives (depending on the tool’s scope).