Design Principles
Design principles are shared guidelines a team uses to make and defend design decisions, especially when two options both look reasonable.
Some are broadly true, like the way people group things that sit close together. Others are choices a specific team makes about what its product should favour. Both work best written down, because a principle nobody can point to cannot settle an argument.
Types
Visual principles govern how a layout reads before anyone starts reading.
- Contrast. Difference in size, weight or colour. Creates emphasis and directs the eye.
- Alignment. Elements sharing an edge look deliberate. Being a few pixels out looks careless.
- Proximity. Things placed close together are read as related, with no label needed.
- Hierarchy. Establishes what to notice first, built from size, weight and position together.
Interaction principles govern what happens once someone acts.
- Feedback. Every action needs an acknowledgement, or people press the button again.
- Consistency. The same action behaving the same way lets people reuse what they learned.
- Forgiveness. Undo and confirmation make mistakes cheap.
How it works
Principles are directional. "Prefer clarity over cleverness" does not tell you what to build, but it tells you which of two options this product favours.
Guidelines are the specific rules underneath them: body text meets a 4.5:1 contrast ratio, touch targets are at least 44 by 44 pixels.
You need both. Principles without guidelines get applied inconsistently across a team. Guidelines without principles become rules people follow without understanding, which makes them brittle the moment an unusual case arrives.
Common mistakes
- Writing principles nobody could disagree with. "Be user friendly" cannot decide anything. A useful principle names a trade-off, so it can pick a side when two options both look defensible.
- Reinventing the well established. Adopt known usability heuristics rather than deriving your own version of "provide feedback". Save the authoring effort for choices genuinely specific to your product.
- Leaving them in a slide deck. A principle that lives where nobody works is not a principle.
Key takeaways
- Write principles down so decisions can be argued from something shared.
- A principle that names no trade-off cannot settle anything.
- Guidelines make principles checkable. You need both.
- Prefer principles grounded in perception over principles grounded in taste.
Learn this
Lessons and exercises mapped to this concept.
Common questions
- What is the difference between a design principle and a design guideline?
- A principle is directional and needs judgement, such as preferring clarity over cleverness. A guideline is specific and checkable, such as requiring body text to meet a 4.5:1 contrast ratio. Principles help a team reason about situations nobody wrote a rule for. Guidelines stop the common cases being re-argued every time.
- Should a team write its own principles or adopt existing ones?
- Both, at different levels. Adopt established usability heuristics, because they are well evidenced and rewriting them wastes effort. Author your own for the choices genuinely specific to your product, such as what to favour when speed and richness pull in opposite directions.
- How do I know a principle is working?
- It gets cited in real disagreements and it changes outcomes. If a team debates two options and nobody reaches for the principles, they are either not known, not specific enough, or not actually the ones the team believes.