The following factors make a website user interface usable:

1. System Feedback:

   The basic idea behind system feedback is to intimate end users regarding what is going on in the system at any given point of time. A well designed system provides users with appropriate feedback, acknowledgements, follow ups and indication that an action request has been carried out.

2. Consistency:

   Look, feel and behaviour of message display methods, colour use, key definition etc must be constant throughout the application. Consistency reduces the amount of uncertainty that user faces when using the interface thereby reducing the erroneous interpretations or actions that user makes.

3. Error Prevention:

   The user interface should be designed in such a way that it should help users to avoid making errors. It will reduce the level of frustration the user is likely to experience with the user interface thereby bringing about greater acceptance of the user interface by the user. Various aspects that need to be taken into account in error prevention include:

4. Number of errors encountered during task.
5. Number of wrong key strokes
6. Number of time the same key is pressed without the desired response.

7. Number of extra key presses that are unnecessary.

8. Performance/Efficiency:

   Performance or efficiency is a quality of user interface that determines how effectively or efficiently the user can complete his tasks. Various components of Performance and efficiency include:

9. Number of goals/tasks not achieved.
10. Time taken for task completion.
11. Unproductive period.

12. Percentage of tasks not completed.

13. Like/Dislike:

    Like/Dislike factor measures user preference. It basically indicates the level of satisfaction that the user feels with the system and user interface.

14. Error Recovery:

    Error recovery is that quality of the system of the user interface which allows the user to exit from a situation that the user did not intend to be in. Users frequently choose the wrong option or enter the wrong data and they are likely to find themselves in a error state from which they need to recover. Recovery from error includes number of components including:

15. Number of times user has to redo the task.
16. Number of times user did not continue.
17. Number of actions taken that does not solve the problem.
18. Percentage of all time spent on error recovery.