What is usability?

by | Dec 23, 2023 | Usability | 0 comments

What is Usability?

The English term “Usability” refers to the “ease of use” of a human-machine interface. Often, usability is also translated as user-friendliness. However, the terms user-friendliness or user-friendliness are not technically correct. Nevertheless, this translation has become common in practice and is acceptable. The term usability is ISO-standardized. According to ISO standard 9241-11, usability refers to “the extent to which a product, system, or service can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction.” In short: Usability ensures that digital applications are easy to use and is measured by how directly and quickly the user can achieve their goal during the use of the application.


Now that we know what usability is, have we covered the most important thing? Unfortunately, no. Because good usability is rarely noticed, while poor usability is. An application has a high degree of usability if the requirements of the guideline for the design of user interfaces according to DIN EN ISO 9241 are met. According to DIN EN ISO 9241, an application should be:

  • appropriate to the task,
  • self-descriptive,
  • controllable,
  • conform to user expectations,
  • error-tolerant,
  • customizable, and
  • promote learning

These 7 requirements are also considered the pillars of usability. At this point, you have a rough idea of what usability is. But now we get to the nitty-gritty. Now we will take a closer look at these 7 pillars of usability. But beware: The article has a total length of 1,886 words. If you don’t have enough time to read the article now, I recommend you bookmark it so you can finish reading it at a later time. The goal of the article is to illuminate the concept of usability in its facets.

Task Appropriateness:

A dialogue is task-appropriate if it supports the user in completing their task effectively and efficiently. This definition includes the 3 criteria for ensuring task appropriateness:

  1. Define the task It is necessary to first identify the tasks that the visitor of a website wants or should perform. These tasks should be documented in writing and revisited during development to check the degree of goal achievement.
  2. Effectiveness To ensure effectiveness, it must be defined when a task is considered successfully completed.
  3. Ensure efficiency Ensuring efficiency is the next logical step: The optimal path must be defined. Specifically, this means that the user must reach the goal with as little expenditure of time, patience, memory performance, and transfer effort as possible.



A dialogue is self-descriptive if each individual dialogue step is immediately understandable through feedback from the dialogue system or is explained to the user upon request. The user must be able to answer the following three questions at any time:

  1. Where do I come from?
  2. Where am I?
  3. Where can I go from here?

To enable the user to answer these questions, they must be supported in the following aspects:

Orientation At every page and in every step of a task to be completed, the visitor must be offered orientation points so that they immediately recognize where in the page hierarchy they are or how far they are from the goal. On websites, so-called “breadcrumbs” are often used, for example: Website -> Shop -> Category -> Product A -> Reviews

Anticipatability A page becomes controllable and manageable for a visitor only when they can navigate with certainty. However, this requires that the visitor can recognize where the navigation elements will lead them based on their design.

Feedback Feedback on the success of actions performed creates a feeling of security in the visitor, which is crucial for building trust.

Help Especially for inexperienced visitors, more complex tasks are often difficult to perform. They should be supported with special assistance or documentation of the system in completing their tasks.

Conformity to Expectations:

A dialogue is conforming to expectations if it is consistent and matches the characteristics of the user, e.g., the knowledge from the work area, the user’s education and experience, and generally accepted conventions. It is important to distinguish who the target audience is. An application for safety calculations for mechatronics engineers does not need to be understood by a hairdresser. On the other hand, a mechatronics engineer does not need to understand an online shop where hairdressers can buy their tools. Humans are creatures of habit. Their actions are shaped by behavioral patterns learned over the course of their lives. Thus, the behavior of visitors on websites is also influenced by various cognitive, behavioral, and learning psychological factors:
Consistency The human brain can grasp connections more quickly when familiar patterns are recognized. If many important features for recognizing, for example, navigation options vary from page to page, the user cannot store a pattern that would facilitate navigation on the next page. Thus, they are repeatedly occupied with recognizing and storing patterns on each page.

Experience Studies have shown that inexperienced users have no preferences regarding navigation, wording, and workflows in many respects. However, the longer visitors have been able to gather experiences with different websites, the greater their demands become regarding conformity with their expectations on newly visited websites. As an example, consider the so-called “burger menu” (the three lines stacked on top of each other): The symbol is anything but intuitive. Users who have never seen the symbol do not know what happens when they click on it. Only through their experiences do they learn this symbol and recognize it in different scenarios.

Error Tolerance

“Dialogue is error-tolerant if the intended work result can be achieved despite erroneous inputs either with no or minimal correction effort by the user.” Potential errors can be classified as follows:

Avoidable Errors “Avoidable errors” often occur due to a lack of engagement with user behavior and could have been avoided with careful target group research. Typical avoidable user errors in applications or on websites are navigation errors due to a lack of orientation options, or incorrect entries on forms due to ambiguous wording. Many software errors caused by programming errors, which produce incomprehensible error messages, are also avoidable. Most of these errors could be avoided through comprehensive testing before launching an application.

Known, Unavoidable Errors Unfortunately, not all known errors can be avoided. Accidentally submitting a form that has not been fully completed, or a typo on the keyboard are just two of countless examples of errors that must be expected. For this type of error, there is usually a simple and clearly recognizable correction possibility. Especially with forms, data validation can catch many errors and give the user the opportunity to make complete/correct entries.

Unanticipated Errors Unanticipated errors occur due to unexpected visitor behavior, or in special cases that trigger hardly identifiable programming errors in advance. Most often, such errors lead to debug messages in the browser, which are not understandable for the user. For example, web codes: 404 – Page Not Found is usually caught, but the status code 503 Internal Server Error is not. Users do not understand why the system is not working and leave the application/website again. These types of errors are so severe because the user loses trust in the application and thus in the company.

Error Prevention Through careful planning of the website structure and intuitive navigation, as well as data validation, many errors can already be avoided.

Error Correction Errors that are known but cannot be completely excluded should create clear and easily understandable ways to help the user independently correct these errors. As mentioned earlier, most “404 Page Not Found” errors are caught. Then a page is loaded that explains to the user that the link was wrong and offers a search function. This allows the user to continue their task without having to leave the site.




A dialogue is controllable if the user can initiate the dialogue process and influence its direction and speed until the goal is reached. Applications and websites are fundamentally unknown territory for users. In unfamiliar terrain, users behave insecurely, uncoordinated, and aimlessly. The more options shown to them, the more coordinated and purposeful they will act. If the dialogue is then controllable for the user, they lose the fear of making mistakes and handle the application more relaxed than otherwise. There are many ways to convey the feeling of controllability to the visitor and give them the opportunity to do so:

  • Options to use or turn off media. The auto-play function of videos has NO place on websites!
  • Alternative navigation options in the text, in a sidebar, or through swipe gestures.
  • Ensuring the correct functioning of the back button or browser function.
  • Always possible accessibility of the homepage
  • Options to cancel at various points

Users are inevitably restricted in their freedom of action, as the number of implemented functions and navigation options is determined by the developer. However, his task is to convey the greatest possible freedom and self-determination in the application to the user. This is achieved by ensuring that the offered options match the expectations of the target group so well that there is no need for more freedom of action.



A dialogue is customizable if the dialogue system allows adjustments to the requirements of the work task, individual preferences of the user, and user capabilities. Not every application must allow individual settings to be made. However, every application should be designed in such a way that at least the customization options provided in the browser/operating system work flawlessly. For example, the zoom functionality, changing the font size, swapping or turning off stylesheets, or deactivating multimedia elements without completely losing the content context. The more a user is required to engage in dialogue, the more customization options must be offered to them. In forums, communities, eCommerce accounts, and other systems that are geared towards regular and frequent dialogue, the offer of personal settings is mandatory and indispensable.

Promoting Learning

A dialogue is conducive to learning if it supports and guides the user in learning the dialogue system. The extent to which learning-promoting measures are necessary directly depends on the deviation of a dialogue from the cognitive patterns stored by the user. These are based on experience with other applications and websites and enable them to adapt their knowledge to new websites. Simply put: If the user can use the experience from other websites and applications to use your application, then you have done everything right. Of course, there are not tested pattern solutions for all content and application cases. Moreover, it is not desirable that all systems are designed the same just to fit into the stored cognitive patterns. However, there is a basic rule about the tolerable level of cognitive capacity strain: “The less often a visitor visits a website, the less they should have to learn how to use it.” No matter how complex the dialogue to be depicted may be, your target group always has a treasure trove of cognitive models that allow them to operate a system designed for these patterns with minimal transfer effort. In the rarest cases, the path leading to the achievement of typical application goals is so complex that the user must be expected to learn a new type of navigation or the processing of certain tasks. For inexperienced visitors, however, there are various aids such as:

  • logical structure of the page
  • logical processes
  • help pages
  • FAQ
  • guided tour
  • visual guiding

However, it should not be forgotten that these aids must also be usable to avoid the need for help with the help 😉


I will forego a long conclusion. The article is long enough as it is. All 7 basic pillars together result in a high degree of usability. Every designer and every web developer should consider these fundamentals in the development of systems. In addition to usability, there is also the term User Experience (UX) and UX Design.