Jenner is a Web page templating system with a twist: it runs completely within a Web browser. Templates are just normal Web pages with special syntax inside text nodes, attributes, or comments. Unlike other in-browser templating systems, Jenner does not require overloading of "class" attributes or invalid HTML; all Jenner templates are valid Web pages and the template expressions flow in a very natural way. Having the template engine in the Web browser instead of on the server takes a lot of load off of the server, and makes for a clean separation of presentation and content. Jenner is very powerful: it has the full power of the Esel expression language at its disposal. Templates can be rendered from JSON data, and can be re-rendered without a browser-to-server round trip.