StuffIt file signature
Magic number at the start of the file · SIT!.
Classic StuffIt archives from the Mac OS 8/9 era begin with the ASCII bytes SIT! followed by a NUL. The later StuffIt X (.sitx) format replaced this with its own header, so the two generations are easy to tell apart.
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 53 49 54 21 00 (the text SIT!.), it is a StuffIt file.
Formats that use the 53 49 54 21 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.sit
- hexdump -C -n 16 example.sit
- file example.sit
Windows (PowerShell)
- Format-Hex -Path example.sit -Count 16
Python
- open("example.sit","rb").read(5).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the StuffIt file signature?
StuffIt files start with the hex bytes 53 49 54 21 00 (SIT!. 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.sit on Linux or macOS, or Format-Hex -Path example.sit -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the StuffIt signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine StuffIt file has these exact bytes; a file with the wrong bytes is not really StuffIt, whatever its name says.