The new version of HTML5 introduced in 2014 includes ten new structural elements. The aim of this research project is to discover whether CAT tools are prepared to localise HTML5 or not, and to determine which of the two tools studied, MemoQ 2013 and SDL Trados Studio 2014, is the most suitable when localising a HTML5 website with HTML5 new structural elements. With this purpose, an experiment was designed and implemented at the University of Geneva (UNIGE). Fourteen students of the Faculty of Translation and Interpreting at the UNIGE participated. The experiment lasted approximately 1.5 hours and included an introductory activity with MemoQ 2013 (due the participants' lesser familiarity with this tool), a background questionnaire, a website localisation task, and a task questionnaire. The results obtained show that both tools are able to process HTML5 and the according to the characteristics evaluated, effectiveness, satisfaction, and context coverage, they are both appropriate for localising a HTML5 website.