How to use hexdecoder.com to decode hexadecimal codes. Hexadecimal is a very confusing and hard-to-read system of numbers that is used to identify colors, alphanumerics, and other symbols and letters. There are many places where this method is used and many of them will not be familiar to people. The website hexdecoder.com makes it very simple to convert any code into plain text so that it is easy to understand.