The idea of escaping things for HTML isn't specific to JSON, but this particular mechanism of escaping is.

Firstly, in typical HTML, a slash is a safe character which won't need escaping. You'd normally need to escape "<" and "&" characters (and quotes if you're outputting data within an attribute), though often ">" is escaped for symmetry. However, as you're outputting the JSON within a <script> element, the usual escaping isn't necessary and (unless you're serving your HTML as XHTML with an XML media type) will not work. HTML::Entities will not work for this purpose. However, the combination of "</" is still dangerous so needs escaping. Escaping "/" as "\/" is specific to Javascript/JSON strings, not a general HTML thing.