UX Foundations

This skill provides the core UX knowledge base that underpins all interface design work. It covers four pillars:

1. Usability Heuristics -- Nielsen's 10 principles for evaluating any interface
2. UX Psychology -- Cognitive laws governing how users perceive, decide, and act
3. Accessibility (WCAG 2.2 AA) -- Requirements for inclusive, standards-compliant interfaces
4. Design System Fundamentals -- Spacing, typography, color, and layout specifications

Apply these foundations universally -- they hold true for SaaS dashboards, landing pages, admin portals, mobile apps, and any web-based interface.

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Nielsen's 10 Usability Heuristics (Quick Reference)

#	Heuristic	Core Rule
1	Visibility of system status	Always inform users about what is happening through timely, appropriate feedback.
2	Match between system and real world	Use language, concepts, and conventions familiar to the user, not internal jargon.
3	User control and freedom	Provide undo, redo, cancel, and clear exit paths -- users will make mistakes.
4	Consistency and standards	Follow platform conventions; identical actions must produce identical results everywhere.
5	Error prevention	Design constraints and confirmations that prevent errors before they occur.
6	Recognition rather than recall	Make elements, actions, and options visible so users never need to memorize.
7	Flexibility and efficiency of use	Offer shortcuts and customization for experts without confusing novices.
8	Aesthetic and minimalist design	Remove every element that does not serve a clear purpose; information competes for attention.
9	Help users recognize, diagnose, and recover from errors	Write error messages in plain language, identify the problem specifically, and suggest a fix.
10	Help and documentation	Provide searchable, task-focused help that is easy to find and contextually relevant.

Full details with violation examples, good implementation examples, and checkable audit items: see references/nielsen-heuristics.md

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Key UX Psychology Laws (Quick Reference)

Law	Core Rule
Fitts's Law	Make targets large and close to the user's focus area -- time to reach a target depends on its size and distance. Min touch target: 44x44px (WCAG), 48x48px (Material).
Hick's Law	Limit choices to reduce decision time -- keep primary navigation to 5-7 items, use progressive disclosure, and break complex decisions into sequential steps.
Miller's Law	Working memory holds 7 +/- 2 items -- chunk information into groups of 3-4, limit steps in wizards, and use external memory aids.
Cognitive Load Theory	Minimize extraneous load (visual clutter, inconsistency), simplify intrinsic load (break tasks into steps), and maximize germane load (use familiar patterns to aid learning).
Gestalt Principles	Users perceive visual groups based on proximity, similarity, closure, continuity, figure-ground, common region, and symmetry -- use these to structure layouts.
Von Restorff Effect	An item that stands out from its group is more likely to be remembered -- use visual distinction for primary CTAs and critical information.
Jakob's Law	Users spend most of their time on other sites and expect similar patterns -- follow established conventions rather than reinventing interactions.

Full details with specific measurements, UI applications, and examples: see references/psychology-laws.md

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UX Scoring Rubric (Quick Reference)

Score each dimension from 1 (poor) to 10 (excellent). Global score = sum of 10 dimensions (max 100).

Dimension	1-3 (Poor)	4-6 (Adequate)	7-10 (Excellent)
Navigation	Users cannot find core features	Users find features with some searching	Users find everything instantly
Clarity	Users do not understand what to do	Users figure it out with effort	Intent is immediately clear
Feedback	No response to user actions	Basic loading/success states	Rich, contextual feedback for every action
Error Handling	Errors cause data loss or dead ends	Errors caught with generic messages	Errors prevented, with specific recovery guidance
Consistency	Every page feels like a different app	Most patterns are consistent	Complete pattern consistency throughout
Accessibility	Keyboard unusable, no alt text	Partial WCAG compliance	Full WCAG 2.2 AA compliance
Performance	LCP > 5s, significant CLS	LCP 2.5-4s, some layout shift	LCP < 2.5s, CLS < 0.1, FID < 100ms
Mobile	Broken on mobile	Functional but awkward on mobile	Native-quality mobile experience
Visual Design	Cluttered, no hierarchy	Clean with some hierarchy issues	Clear hierarchy, purposeful whitespace, polished
Content	Jargon-heavy, unclear	Mostly clear, some jargon	Scannable, user-centered, helpful

• Below 60/100 = Critical attention needed
• 60-80/100 = Solid foundation with room for improvement
• Above 80/100 = Strong UX

When auditing, score each dimension independently and include a 1-sentence justification per score.

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Core Accessibility Requirements (WCAG 2.2 AA)

Apply these four requirements to every interface without exception:

1. Color Contrast

• Normal text (under 18px bold or 24px regular): minimum 4.5:1 contrast ratio
• Large text (18px+ bold or 24px+ regular): minimum 3:1 contrast ratio
• Non-text UI elements (icons, borders, form controls): minimum 3:1 contrast ratio
• Never use color as the sole means of conveying information -- always pair with text, icons, or patterns

2. Touch and Click Targets

• Minimum target size: 44x44 CSS pixels (WCAG 2.2), 48x48px recommended (Material Design)
• Minimum spacing between adjacent targets: 8px
• Place primary actions in the thumb zone (lower third of mobile screens)

3. Keyboard Navigation

• All functionality must be operable via keyboard alone
• Focus indicator must be visible: minimum 2px outline with 3:1 contrast against adjacent colors
• Focus order must follow logical visual reading order
• No keyboard traps -- users must be able to Tab away from every element
• Provide a skip-navigation link as the first focusable element

4. Screen Reader Support

• All images require alt text (decorative images use alt="")
• Form inputs must have associated <label> elements or aria-labelledby
• Dynamic content updates require aria-live regions
• Use semantic HTML (<nav>, <main>, <section>, <header>, <footer>) as the foundation
• Custom interactive components require appropriate ARIA roles, states, and properties

Complete WCAG 2.2 AA checklist with POUR principles, ARIA patterns, and screen reader considerations: see references/accessibility-wcag.md

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Design System Essentials

Spacing Grid (4pt base)

Use multiples of 4px for all spacing, padding, and margin values: 4, 8, 12, 16, 20, 24, 32, 40, 48, 64, 80, 96

• Tight (4-8px): icon-to-label gaps, inline element spacing
• Default (12-16px): form label to input, component internal padding
• Loose (24-32px): between components within a section
• Section (48-96px): between major page sections

Typography Scale

Base size: 16px body text. Apply a modular scale ratio:

Ratio Name	Value	Best For
Major Second	1.125	Dense data UIs
Minor Third	1.200	Text-heavy SaaS interfaces
Major Third	1.250	General purpose, versatile
Perfect Fourth	1.333	Marketing and content sites
Augmented Fourth	1.414	Editorial, blog layouts
Perfect Fifth	1.500	Presentation-style layouts
Golden Ratio	1.618	Landing pages, high drama

Recommended type ramp (px): 12, 14, 16, 18, 20, 24, 30, 36, 48, 60, 72

Limit distinct sizes to 6-8 across the product. Use font weight (regular, medium, semibold, bold) as a secondary hierarchy tool.

Breakpoints

Token	Width	Target
mobile	320px	Small phones
mobile-lg	480px	Large phones
tablet	768px	Tablets (portrait)
laptop	1024px	Small desktops, landscape tablets
desktop	1280px	Standard desktops
desktop-lg	1440px	Large desktops
wide	1920px	Full HD monitors

Complete design system reference with color systems, border radius, shadows, elevation, and z-index scale: see references/design-systems.md

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Reference Files

For detailed, audit-ready content on each pillar, consult:

File	Contents
references/nielsen-heuristics.md	Full Nielsen's 10 heuristics with violation examples, good examples, and checkable audit items
references/psychology-laws.md	Complete UX psychology laws with specific measurements, UI applications, and cognitive load theory
references/accessibility-wcag.md	Full WCAG 2.2 AA reference with POUR checklists, ARIA patterns, and screen reader guidance
references/design-systems.md	Complete design system specifications with spacing, typography, color, shadows, z-index, and breakpoints