Web usability relates to usability on the internet. Websites are user friendly, if they enable users to reach their goals effectively, efficiently and satisfactorily. There are very specific guidelines for interactive user interfaces like web sites. The standard ISO 9241 states, that good usability is guaranteed, if the design is suitable for the task, self-descriptive, suitable for learning, controllable, conformable with user expectations, suitable for individualization and error tolerant.