GIF file signature
Magic number at the start of the file · GIF8
A GIF opens with the ASCII text GIF8 and then the version, either 37 61 (GIF87a) or 39 61 (GIF89a). GIF89a added transparency and animation, so a file starting GIF89a can be animated.
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 47 49 46 38 (the text GIF8), it is a GIF file.
Signature variants
GIF appears with more than one byte pattern. These all identify the same family:
| Hex signature | Offset | Note |
|---|---|---|
| 47 49 46 38 37 61 | 0 | GIF87a |
| 47 49 46 38 39 61 | 0 | GIF89a |
Formats that use the 47 49 46 38 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.gif
- hexdump -C -n 16 example.gif
- file example.gif
Windows (PowerShell)
- Format-Hex -Path example.gif -Count 16
Python
- open("example.gif","rb").read(4).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the GIF file signature?
GIF files start with the hex bytes 47 49 46 38 (GIF8 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.gif on Linux or macOS, or Format-Hex -Path example.gif -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the GIF signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine GIF file has these exact bytes; a file with the wrong bytes is not really GIF, whatever its name says.