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Postel’s Law in UX Design: Striving for Robust and User-Friendly Experiences

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In the world of UX (User Experience) design, the ability to create intuitive and user-friendly digital experiences is paramount. To achieve this, we can draw inspiration from various principles and guidelines. In this article at OpenGenus, we are going to talk about one such principle that holds great significance in UX design which is Postel's Law.

Table of contents:

  1. What is Postel’s Law?
  2. Examples
  3. Conclusion

What is Postel’s Law?

Postel's Law states, "Be conservative in what you do, be liberal in what you accept." Let's break down this statement to grasp its implications. "Be conservative in what you do" suggests that designers should establish strict guidelines and adhere to established standards when creating UX systems. It promotes consistency, predictability, and a strong foundation for users to rely on. By setting clear boundaries, designers can create intuitive interfaces that are easy to understand and navigate.

On the other hand, "be liberal in what you accept" implies that designers should be more forgiving when it comes to interpreting and handling user inputs. It acknowledges the fact that users can exhibit a wide range of behaviors and may not always adhere to the expected patterns. Embracing this principle ensures that UX systems can handle diverse inputs gracefully, reducing friction and frustration for users.


At its core, Postel's Law encourages designers to prioritize compatibility and resilience in their designs. Let's explore how this principle can be applied in various aspects of UX design, with relevant examples to illustrate its effectiveness.

1. Input Validation and Error Handling:

Postel's Law suggests that we should be liberal in what we accept, meaning we should strive to be lenient when users input information. By anticipating and accommodating a wide range of user inputs, we can enhance the overall usability of our designs. For instance, if a user mistakenly inputs a phone number without including dashes or spaces, a well-designed form could automatically format it correctly or provide clear instructions on how to enter the information.

2. Data Formatting and Transformation:

When dealing with data, Postel's Law encourages designers to be conservative in what they send. It emphasizes the importance of providing output in a format that is familiar and compatible with the users' expectations. Consider an e-commerce platform that allows users to enter their payment information. If the platform automatically reformats the credit card number by inserting spaces after every four digits, it can help users easily verify and validate their input.

3. Content Presentation and Readability:

In the realm of content presentation, Postel's Law suggests being conservative in what we send. Designers should prioritize clear and concise communication, ensuring that information is presented in a manner that is easily digestible for users. For example, a news website that presents articles with long paragraphs and dense blocks of text may overwhelm readers. By breaking down the content into smaller sections, incorporating subheadings, and utilizing bullet points, the design can enhance readability and improve the overall user experience.

4. Error Messages and Feedback:

Error handling is an essential aspect of UX design, and Postel's Law can guide us in this area as well. When an error occurs, designers should be liberal in what they accept, providing meaningful and helpful feedback to users. Instead of displaying cryptic error messages, UX designers can strive to offer clear and actionable guidance. For instance, if a user submits a form without completing required fields, the error message can specify which fields need to be filled out, allowing the user to rectify the issue easily.

5. Cross-Browser and Cross-Device Compatibility:

In today's multi-device and multi-browser landscape, ensuring compatibility across various platforms is crucial. Postel's Law reminds designers to be conservative in what they send, considering the limitations and differences of different devices and browsers. By adopting responsive design techniques, such as fluid layouts and flexible media, we can create designs that adapt to different screen sizes and resolutions, providing a consistent and optimized experience for users regardless of their device or browser choice.

6. Human-Computer Interaction:

Postel's Law can also be applied to the interaction between users and digital interfaces. Designers should strive to be conservative in what they request from users, minimizing cognitive load and streamlining interactions. For instance, when designing a checkout process, unnecessary steps and form fields should be eliminated to reduce friction and improve conversion rates. By requesting only essential information and leveraging autofill features, we can make the experience more efficient and user-friendly.

7. Accessibility and Inclusivity:

Postel's Law can significantly contribute to creating accessible and inclusive user experiences. Being conservative in what we send means designing interfaces that are compatible with a wide range of assistive technologies and accommodating to users with diverse abilities. For example, providing alternative text for images, ensuring proper color contrast for text and background, and implementing keyboard navigation options are all practices that align with Postel's Law and promote a more inclusive design approach. By accepting a variety of inputs, such as different interaction methods like touch, mouse, or keyboard, designers can cater to users' individual needs and preferences.

8. Internationalization and Localization:

When designing digital experiences for a global audience, Postel's Law encourages designers to be conservative in what they send and liberal in what they accept in terms of cultural and linguistic differences. Designers should aim for designs that can be easily localized and adapted to different languages, writing systems, and cultural norms. By considering variations in content length, text direction, date and time formats, and other localization aspects, designers can create experiences that feel native and resonate with users from different regions.

9. Iterative Design and User Feedback:

Postel's Law aligns with the iterative design process and the importance of user feedback. By being liberal in what we accept, designers welcome user insights and suggestions, fostering a collaborative approach to improving the user experience. Actively seeking user feedback, conducting usability tests, and analyzing user behavior allows designers to understand user expectations and preferences better. This iterative feedback loop empowers designers to refine and enhance their designs continuously, resulting in more user-centric experiences.

10. Continuous Improvement and Future-Proofing:

Postel's Law emphasizes resilience and adaptability in UX design. By being conservative in what we do and considering potential future changes and advancements, designers can future-proof their designs to some extent. Anticipating technological advancements, evolving user needs, and emerging trends allows designers to build scalable and adaptable designs that can withstand the test of time. Applying flexible design patterns and modular approaches enables seamless integration of new features and functionalities, ensuring a positive user experience even as the digital landscape evolves.


In conclusion, Postel's Law offers valuable insights for UX designers aiming to create effective and user-friendly digital experiences. By being conservative in what we send and liberal in what we accept, we can design interfaces that accommodate user preferences and behaviors while maintaining compatibility and resilience. From input validation to content presentation and error handling, incorporating Postel's Law into our design process can lead to more intuitive and satisfying user experiences.

Postel’s Law in UX Design: Striving for Robust and User-Friendly Experiences
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