What are magic bytes?

Magic bytes (or a file signature) are a short, fixed sequence of bytes at the very start of a file that identifies its format. For example, every PNG begins with the bytes 89 50 4E 47 and every PDF begins with 25 50 44 46 ('%PDF'). Tools read these bytes to determine the true file type regardless of the file's name.

Why does the extension not always match the content?

Anyone can rename a file. Attackers commonly disguise an executable or script as a harmless .jpg or .pdf. Because the operating system and many applications trust the extension, checking the magic bytes reveals the real format and exposes the deception.

Is my file uploaded anywhere?

No. Only the first bytes of the file are read locally in your browser using the FileReader API. The file never leaves your device.

Why is no type detected?

Plain text, CSV, source code and many proprietary formats have no fixed magic number. The tool will report that the header does not match a known signature and show the raw hex so you can inspect it.

File Signature / Magic Bytes Identifier

Drag & drop a file to read its magic bytes, identify the true file type and flag mismatched or spoofed extensions. Only the first bytes are read · the file never leaves your device.

File

Click to select or drag & drop a file

Detection

Drop a file to begin.

Related tools

How to use

Drop a file

Only the first 64 bytes are read · nothing is uploaded.

Read the verdict

The detected type is compared against the file's extension.

Inspect the header

View the raw hex and ASCII of the file's leading bytes.

Frequently Asked Questions

A short fixed byte sequence at the start of a file that identifies its format · e.g. PNG starts with 89 50 4E 47, PDF with %PDF. They reveal the true type regardless of file name.

Anyone can rename a file. Attackers disguise executables as .jpg or .pdf. Checking magic bytes exposes the real format.

No. Only the first bytes are read locally via the FileReader API. The file never leaves your device.

Plain text, CSV, code and many formats have no magic number. The tool reports no match and shows the raw hex.

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