Starting with Concept Server 4.0 a new client was introduced. Concept Client 4.0 JS is a pure JavaScript implementation of the concept protocol, on top of web sockets. Almost any native concept:// application could be run directly in browser, without the need for Concept native client.

The JS client was tested on Chrome, Firefox, Opera, Safari, WebKit engine (used by many browsers) and Internet Explorer 11 (partially supported).