UX Design Principles

Psychology-backed decision framework for agents building user interfaces.

Reference: Laws of UX, 2nd Ed. (Yablonski, O'Reilly), Don't Make Me Think, Revisited (Krug, New Riders), The User Experience Team of One (Buley, Rosenfeld Media)

These principles derive from human cognition, not trends. They apply regardless of framework, platform, or era.

When to Use

• Building UI components (buttons, forms, navigation, modals, menus, lists)
• Reviewing existing interfaces for usability problems
• Choosing between interaction patterns (dropdown vs. radio, modal vs. inline)
• Designing navigation structure or information architecture
• Reducing cognitive load in complex interfaces
• Auditing for dark patterns or manipulative design
• Handling errors, empty states, and loading states

Don't use for: typography decisions, color/palette generation, responsive CSS layout, or design token creation.

The Five UX Decisions

Apply these to every UI element you build:

Quick Principle Index

Laws of UX — see references/laws-of-ux.md:

• Fitts's Law — larger, closer targets are faster to reach
• Hick's Law — fewer choices = faster decisions
• Jakob's Law — match existing mental models and conventions
• Miller's Law — chunk information into groups of 3-7
• Peak-End Rule — users judge by the peak moment and the ending
• Aesthetic-Usability Effect — polished UI is perceived as more usable
• Von Restorff Effect — the visually different item is the one remembered
• Tesler's Law — absorb complexity in the system, not the user
• Doherty Threshold — respond within 400ms or show progress
• Postel's Law — accept liberal input, produce strict output

Usability Heuristics — see references/usability-heuristics.md:

• Self-evidence — pages should be obvious, not require thought
• Scanning over reading — users scan in F-pattern; design for it
• Satisficing — users pick the first reasonable option, not the best
• Omit needless words — halve word count, then halve again
• Navigation conventions — persistent nav, "you are here", Trunk Test

UX Process — see references/ux-process.md:

• Fresh Eyes Heuristic Walk — 7-step agent self-review procedure
• Proto-Personas — lightweight user models for design decisions
• Nielsen's 10 Heuristics — mapped to code-level checks

Component-Level Quick Reference

Buttons and CTAs:

• Primary action visually dominant (Von Restorff) and largest target (Fitts's)
• Max 1 primary + 1-2 secondary actions per view (Hick's)
• Labels: verb+noun — "Save Draft", "Delete Account", not "Submit" or "OK" (self-evidence)

Forms:

• Group related fields; max 5-7 per group (Miller's)
• Accept liberal input: phone, date, address in any format (Postel's)
• Inline validation within 400ms (Doherty); errors on the field, not in a banner
• Mark the worst errors first (Peak-End)

Navigation:

• Match industry conventions for position and structure (Jakob's)
• Max 7 top-level items; group beyond that (Miller's + Hick's)
• Persistent nav on every page with "you are here" indicator (Krug)

Modals and Dialogs:

• One decision per modal (Hick's)
• Destructive actions: specific label — "Delete 3 files", not "Are you sure?" (self-evidence)
• Close button top-right on desktop (Jakob's)

Lists and Menus:

• Highlight the important/different item (Von Restorff)
• Chunk into groups of 3-5 with visual separators (Miller's)
• Most-used items at top (satisficing)

Loading and Feedback:

• 400ms: loading indicator (Doherty)

• 1s: progress bar

• 10s: progress percentage or step count

• Non-destructive actions: consider optimistic UI

Dark Pattern Avoidance

• MUST NOT use confirm-shaming ("No thanks, I don't want to save money")
• MUST NOT make unsubscribe/cancel harder than subscribe
• MUST NOT pre-check consent or opt-in boxes
• MUST NOT make the undesired choice more prominent (misdirection)
• MUST NOT create artificial urgency or false scarcity
• MUST NOT use roach-motel patterns (easy in, hard out)
• Asymmetry test: if the effort to undo exceeds the effort to do, it is likely a dark pattern

References

Load these on demand for detailed guidance:

• references/laws-of-ux.md — Full treatment of all 10 laws with code checks and violation/fix examples
• references/usability-heuristics.md — Krug's principles with navigation rules and the Trunk Test
• references/ux-process.md — Lightweight UX methods: guerrilla testing, proto-personas, heuristic walkthroughs
• references/ux-review-checklist.md — 36-item checklist to run against any interface

Related Skills

No related skills are listed yet. Add entries here only when corresponding skill directories exist in the repo.