The Cognitive Bias Codex

The Cognitive Bias Codex is a handy tool that organizes biases in a meaningful way; however, it is worth pointing out that the codex lists heuristics and biases both as biases. If you decide to rely on this codex, then keep in mind the distinction between heuristics and biases, which described below.

Wikipedia’s list of cognitive biases, grouped into categories. Category model by
Wikipedia’s list of cognitive biases, grouped into categories. Category model by Buster Benson.

We are often presented with situations in life when we need to make a decision with imperfect information, and we unknowingly rely on prejudices or biases.

For example, we might:

  • Trust someone more if they’re an authority figure than if they’re not
  • Assume someone’s gender based on their profession
  • Make poor decisions based on the information that we’re given

The reasons for our poor decision making can be a consequence of heuristics and biases.

A bias is a tendency, inclination, or prejudice toward or against something or someone. Some biases are positive and helpful—like choosing to only eat foods that are considered healthy or staying away from someone who has knowingly caused harm. But biases are often based on stereotypes, rather than actual knowledge of an individual or circumstance. Whether positive or negative, such cognitive shortcuts can result in prejudgments that lead to rash decisions or discriminatory practices.

A heuristic is a mental shortcut that allows an individual to make a decision, pass judgment, or solve a problem quickly and with minimal mental effort. While heuristics can reduce the burden of decision-making and free up limited cognitive resources, they can also be costly when they lead individuals to miss critical information or act on unjust biases.

In general, heuristics and biases describe a set of decision-making strategies and the way that we weigh certain types of information.

The existing literature on cognitive biases and heuristics is extensive, but this section contains user-friendly summaries with sources. Central to this section is how cognitive heuristics and biases influence our decision making and you will also learn more about how to overcome them.

So to improve your user experience, you need to understand the biases & heuristics affecting those four decision-cycle steps. Below is a list of cognitive biases and design principles (with tips and resources) for each category. Let’s dive right in.

The 3 conundrums we must face.


There's too much information to process, and we have limited attention to give, so we filter lots of things out.

Noise becomes signal.

The downside: we don’t see everything. Some of the information we filter out is actually useful and important..


Lack of meaning is confusing, and we have limited capacity to understand how things fit together, so we create stories to make sense of everything.

Signal becomes a story.

The downside: our search for meaning can conjure illusions. We sometimes imagine details that were filled in by our assumptions, and construct meaning and stories that aren’t really there.


We never have enough time, resources, or attention at our disposal to get everything that needs doing done, so we jump to conclusions with what we have and move ahead.

Stories become decisions.

The downside: quick decisions can be seriously flawed. Some of the quick reactions and decisions we jump to are unfair, self-serving, and counter-productive.

The 13 strategic shortcuts we've picked up to compensate.

Filter information

1. Depend on the context.

2. Accept what comes to mind.

3. Amplify the bizarre.

4. Notice the new and different.

5. Seek take-aways.

Confabulate stories

6. Fill in gaps.

7. Favor the familiar.

8. Treat experience as reality.

9. Simplify mental math.

10. Be overconfident.

Jump to conclusions

11. Stick with it.

12. Protect existing beliefs.

13. Do the safe thing.



  • Cognitive bias cheat sheet An organized list of cognitive biases because thinking is hard.
  • The Psychology of Design 106 Cognitive Biases & Principles That Affect Your UX
  • Cognitive biases, Ness Labs The human mind is powerful, but it has limitations. Cognitive biases are systematic errors in thinking that occur when people are processing information. They affect our judgements and the decisions that we make. Being aware of our cognitive biases is the first step in managing them, so we can think and work better.
  • Psychology for UX: Study Guide Unsure where to start? Use this collection of links to our articles and videos to learn about some principles of human psychology and how they relate to UX design.
  • Thinking Tools A collection of 100 mental models, cognitive biases and metacognitive frameworks.