Template escaping is the practice of replacing special characters in user-controlled data so a template engine renders it as plain text instead of interpreting it as code or markup. For example, characters such as <, >, ", and ' are encoded before output, which prevents the browser or renderer from treating the input as HTML, JavaScript, or another executable format.
It matters because many web apps mix trusted page structure with untrusted content like posts, usernames, comments, or profile fields. If escaping is missing or applied in the wrong context, attackers can inject cross-site scripting payloads, alter page behavior, steal sessions, or trigger actions in a victim’s browser. Defenders use context-aware escaping, output encoding, and safe template helpers, plus tests that verify untrusted input is always rendered inert.