File with CERT filename extension are used by Netscape Navigator web browser. CERT files are used for storing security certificates that allow access to websites. CERT file syntax supports certification indexing.

Netscape web browser, which used CERT files extensively, is no longer developed and updated. Last stable version was released in 2008 and the product has been since discontinued by its developer, AOL. Mozilla Firefox, a popular web browser, is the spiritual successor to Netscape.