The Robustness Principle: How Postel’s Law Applies to UX/UI Design and Development

Postel’s Law, also known as the Robustness Principle, is a guideline for software design and development that was formulated by Jon Postel, an early pioneer of the Internet, in 1980. He stated it as follows: “Be conservative in what you do, be liberal in what you accept from others”. Postel was referring to the design of software protocols that enable communication between different computers on the Internet. He suggested that protocols should be strict and consistent in what they send to other machines, but flexible and tolerant in what they receive from them.

Postel’s Law has been widely adopted and applied in various fields of computer science and engineering, and it is also a useful principle for user experience (UX) and user interface (UI) design and development.

How does Postel’s Law apply to UX/UI?

It implies that web designers and developers should be conservative in what they send to users, and liberal in what they accept from users.

Being conservative in what they send means that web designers and developers should follow established standards and best practices when creating UX/UI elements. They should provide clear and consistent information, feedback, and navigation to users, and optimize the performance, accessibility, and usability of their website across different devices, browsers, and platforms.

Being liberal in what they accept means that web designers and developers should anticipate and accommodate a wide range of user inputs, behaviors, and preferences. They should validate and format user inputs to prevent errors and confusion, provide options and alternatives, and design for inclusivity and diversity.

What are the benefits of Postel’s Law for UX/UI?

• Improved compatibility: ensure that your website works well on different devices, browsers, and platforms.
• Enhanced usability: make your website more user-friendly and intuitive.
• Reduced errors: minimize the chances of errors occurring on your website.
• Increased adaptability: make your website more resilient and adaptable to changes.

Examples of Postel’s Law in UX/UI

• Google: conservative in what it sends (a simple, consistent interface optimized across devices), and liberal in what it accepts (any query, with spelling correction, autocomplete, filters, and support for many languages and regions).
• Amazon: conservative in what it sends (a clear and consistent interface), and liberal in what it accepts (any query or browsing path, with spelling correction, autocomplete, comparisons, reviews, and multiple delivery and payment options).

Conclusions

Postel’s Law is a useful principle for web design and development. It suggests that web designers and developers should be conservative in what they send to users, and liberal in what they accept from users. By following this principle, they can create websites that are compatible, usable, reliable, and adaptable.

Bibliography

[1] J. Postel, “Transmission Control Protocol - DARPA Internet Program Protocol Specification,” RFC 793, Sep. 1981.

[2] J. Yablonski, Laws of UX: Using Psychology to Design Better Products & Services. Sebastopol, CA, USA: O’Reilly Media, 2020.