How do I determine if a file is a GIF or webp?

Question

I have a file that's .gif extension but I suspect that it's a lie and it's actually a webp. What's the best way to know what format the file is?

Answer 1

By looking into file content and checking its magic number. For webp it's WEBP and for GIF file it is GIF87a/GIF89a.

Here you have list of all magic numbers and where it is located in file: https://en.wikipedia.org/wiki/List_of_file_signatures