7Z File Signature: 37 7A BC AF 27 1C (Magic Number)

A 7-Zip archive starts with the six-byte signature 37 7A BC AF 27 1C. The first two bytes are the ASCII letters 7z; the remaining four are a fixed binary marker unique to the format.

What this magic number means

A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 37 7A BC AF 27 1C (the text 7z¼¯'.), it is a 7Z file.

Formats that use the 37 7A BC AF signature

These file types in our database carry this signature:

How to check a file's signature

You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.

Linux & macOS

xxd -l 16 example.7z
hexdump -C -n 16 example.7z
file example.7z

Windows (PowerShell)

Format-Hex -Path example.7z -Count 16

Python

open("example.7z","rb").read(6).hex()

In your browser

Drop the file into the WhatFileType identifier, which reads the signature without uploading it.

Frequently asked questions

What is the 7Z file signature?

7Z files start with the hex bytes 37 7A BC AF 27 1C (7z¼¯'. in ASCII). This magic number identifies the format regardless of the file's name or extension.

How do I check a file's magic number?

Open the file in a hex editor, or run a command such as xxd -l 16 example.7z on Linux or macOS, or Format-Hex -Path example.7z -Count 16 in Windows PowerShell, and read the first bytes.

Can a file fake the 7Z signature?

Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine 7Z file has these exact bytes; a file with the wrong bytes is not really 7Z, whatever its name says.

7Z file signature