Files with the .CGI extension contain executable network script code usually written in Perl or C. CGI files are usually used to execute simple web scripts - to send emails using the formmail web form or to swap ads on a website.

CGI files are usually stored in the cgi-bin directory of the website’s server. They can be edited provided they are not pre-compiled beforehand, i.e. if they are saved in text form and not in binary form.