Knowledge base
64 principles that validate every step
Every recommendation the AI gives in Rubik is anchored to one of these real principles, with a citable source and author. Nothing invented, nothing hallucinated.
64 principles
3 Design Processes for High Usability: Iterative Design, Parallel Design, and Competitive Testing
1 principleIterative design — Short evaluation cycles
Each short iteration cycle (evaluate, identify problems, new version) improves the design's measurable usability; iterating on real testing findings pays off more than betting everything on a single "perfect" design from the start.
10 Usability Heuristics for User Interface Design
10 principlesHeuristic #1 — Visibility of system status
The system should keep users informed about what is going on, through appropriate feedback within a reasonable time. Any process longer than 1 second requires visual feedback.
Heuristic #2 — Match between system and the real world
The system should speak the user's language — familiar words, phrases and concepts. Follow real-world conventions, presenting information in a natural and logical order.
Heuristic #3 — User control and freedom
Users make mistakes and need clearly marked emergency exits. Support undo and redo.
Heuristic #4 — Consistency and standards
Users shouldn't have to wonder whether different words, situations or actions mean the same thing. Follow platform conventions.
Heuristic #5 — Error prevention
Even better than good error messages is a careful design that prevents problems. Eliminate error-prone conditions or ask for confirmation before critical actions.
Heuristic #6 — Recognition rather than recall
Minimize the user's memory load by making objects, actions and options visible. The user shouldn't have to remember information from one part of the dialogue to another.
Heuristic #7 — Flexibility and efficiency of use
Accelerators let expert users operate faster. Allow users to tailor frequent actions.
Heuristic #8 — Aesthetic and minimalist design
Dialogues shouldn't contain irrelevant information. Every extra unit of information competes with the relevant ones and diminishes their visibility.
Heuristic #9 — Help users recognize, diagnose and recover from errors
Error messages should be expressed in plain language, precisely indicate the problem and constructively suggest a solution.
Heuristic #10 — Help and documentation
Although it's better if the system doesn't need additional explanation, it may be necessary to provide help oriented to the user's task.
Affinity Diagramming
1 principleAffinity Diagramming
Group individual observations into emerging themes bottom-up, don't impose predefined categories. One insight per note. Look for patterns, don't confirm hypotheses.
Atomic Design
1 principleAtomic Design
Components are built hierarchically: Atoms → Molecules → Organisms → Templates → Pages. Each component should document all its states: default, hover, active, disabled, error, focus.
Card Sorting: Uncover Users' Mental Models for Better Information Architecture
1 principleCard Sorting — Mental Models
Card sorting reveals how users naturally group and name content, not how the team thinks it should be organized. Open (no categories) to discover structure; closed (fixed categories) to validate one that's already proposed.
Content Inventory and Auditing 101
1 principleContent Inventory & Audit
Before redesigning content you have to catalog EVERYTHING that exists (inventory) and evaluate its quality, currency and relevance (audit) — they are two distinct steps. The inventory answers what is there; the audit answers what is useful, what gets updated and what gets removed.
Content Strategy 101
1 principleContent Strategy — Content matrix
A content matrix documents, for each piece, its business purpose, audience, format and owner responsible for maintenance — without that traceability content becomes orphaned and nobody knows why it exists or who updates it.
Contextual Design
1 principleContextual Inquiry
Observe the user in their real environment while they perform real tasks. Context reveals behaviors the user wouldn't report in an interview.
Design Critiques: Encourage a Positive Culture to Improve Products
1 principleDesign Critique — Culture of structured feedback
An effective design review has a clear goal, agenda and facilitation — without structure, it drifts into personal preferences instead of actionable feedback. The focus should be on the user and business problem, not individual tastes.
Design Thinking — HMW Method
1 principleHow Might We — Problem Framing
A good problem statement is user-centered, specific about the problem and broad enough to generate multiple solutions. HMW questions should open up possibilities without dictating a solution.
Design Thinking Bootleg
1 principleIdeation — Generative brainstorming
A good brainstorming session separates generation from evaluation: quantity first without judging, group and evaluate afterwards. Good facilitation opens the space; adding solution constraints generates more original ideas than a blank canvas.
Design Tokens Community Group W3C
1 principleDesign Tokens — Semantic naming
Tokens should be named by their semantic role, not by their value. Correct: color-action-primary. Incorrect: blue-500. Structure: primitives (raw values) → semantic (roles) → components (specific use).
Design Tokens Format Module
1 principleDesign Tokens — Interchange format
Handoff to development becomes reliable when design values (color, typography, spacing) travel as tokens in a standard format, not as screenshots or loose specs — the developer consumes the same data design defined, with no manual transcription.
Discovery: Definition
1 principleDiscovery Stakeholder Interview
Stakeholder interviews should cover: business goals, known constraints, definition of success and perceived risks. Avoid closed questions.
Foundations — Material Design 3
1 principleMaterial Design 3 — Visual foundations
A coherent system of color, typography, motion and shape is what makes a high-fidelity interface feel finished and not just "painted" — each foundation must be defined as a system, not screen by screen.
IA-Based View of Prototype Fidelity
1 principleInteractive prototype fidelity — Scope from an IA perspective
An interactive prototype doesn't need to implement 100% of the information architecture to be useful: it can be limited to a horizontal path (all screens, little depth) or a vertical/semi-complete one (one complete route, the rest not implemented) depending on what you want to validate.
Interaction Design Foundation — Competitive Analysis
1 principleCompetitive Analysis Framework
Analyze direct and indirect competitors across the dimensions of features, strengths and weaknesses to identify differentiation opportunities.
Jobs to Be Done Theory
1 principleJobs to Be Done
People don't buy products — they hire solutions to do a job. Format: "When [situation], I want [motivation], so that [expected outcome]". Distinguish functional, emotional and social jobs.
Journey Mapping 101
1 principleJourney Mapping
An effective journey map covers the whole experience from first contact to completed goal. It should include: phases, user actions, thoughts, emotions and pain points. Base it on real research, not on the team's assumptions.
Laws of UX
10 principlesAesthetic-usability effect
Interfaces perceived as attractive are also perceived as easier to use, and that impression survives even when use proves otherwise. A careless visual finish makes the user attribute problems to the product that it doesn't have, and leave before giving it a chance.
Doherty threshold
Productivity rises when the system responds in under 400 ms: below that threshold the interaction feels instant. Above it, the wait needs a visible signal — skeleton, bar or spinner — or the user assumes something broke and repeats the action or leaves.
Fitts's Law
The time to reach a target is a function of the distance to the target and its size. Small or distant targets increase interaction time and error rate. Minimum touch targets: 44x44px Apple / 48x48dp Google.
Hick's Law
The time to make a decision increases with the number and complexity of the options. Simplify options and use progressive onboarding to reduce cognitive load.
Jakob's Law
Users spend most of their time on other sites. They prefer your site to work the same way as the ones they already know. Following established conventions reduces the learning curve.
Law of Prägnanz
People perceive and interpret ambiguous images in the simplest way possible. Design should reduce visual complexity and communicate with as few elements as possible.
Law of Proximity
Elements close to each other are perceived as a group, even if they don't share color or shape. White space groups better than boxes and lines: a label closer to the next field than to its own reads as belonging to the one it doesn't.
Serial position effect
From a series, the first and last items are remembered; the ones in the middle are lost. What matters most goes at the ends: the primary action at the end of a row of buttons, the most used destination at the start of a menu. Burying what's important in the middle of a list is hiding it.
Tesler's Law — conservation of complexity
Every system has a minimum complexity that can't be eliminated: you only decide who carries it, the product or the person. Every field asked for unnecessarily, every decision delegated without context, is complexity the design saved itself and passed on to the user.
Von Restorff effect — Isolation
When there are several similar elements, the one that differs visually is the one that's remembered and the one that's tapped. A screen's primary action should stand out from the rest by color, size or space; if two or more actions compete with the same weight, none stands out.
Measuring the User Experience on a Large Scale
4 principlesHEART Framework — Adoption & Retention
Adoption: new users who adopt a feature. Retention: users who come back. Indicators: activation percentage, churn rate, DAU/MAU ratio.
HEART Framework — Engagement
Engagement: the user's level of involvement with the product. Indicators: sessions per user, actions per session, time on task.
HEART Framework — Happiness
Happiness: user satisfaction measured with surveys (CSAT, NPS). Indicator: average rating, percentage of satisfied users.
HEART Framework — Task Success
Task Success: efficiency, effectiveness and error rate on key tasks. Indicators: task completion rate, time on task, error rate.
Navigation Design Patterns
1 principlePersonas Make Users Memorable for Product Team Members
1 principleResearch-based Personas
Effective personas are based on real research patterns, not assumptions. They should include: demographics, observed behaviors, motivations, frustrations and main goal. A persona without real research is a proto-persona.
Prioritizing Web Usability
1 principlePrioritization of UX findings
Priority = (frequency × severity) / estimated effort to fix. Fix first: high frequency + high severity + low effort.
Quantitative User Research
1 principleQuantitative UX Research
Analytics data identifies WHAT is happening, not WHY. Combine it with qualitative research for a complete diagnosis. Key metrics: bounce rate, task completion, funnel drop-off.
Research in UX
1 principleSource Credibility in Research
Prioritize primary sources over secondary ones. Check the publication date — UX content older than 5 years may be outdated.
Research Methods in UX
1 principleSecondary Research — Reviews Analysis
Public reviews (App Store, G2, Reddit, Trustpilot) are valid secondary research. Group by theme and sentiment. It doesn't replace primary research — it complements it.
Severity Ratings for Usability Problems
1 principleSeverity Ratings — Nielsen Scale
Severity 1: cosmetic. Severity 2: minor, low priority. Severity 3: major, high priority. Severity 4: catastrophic, must be fixed before launch.
The Design of Everyday Things
1 principleSignifiers and affordances
A control has to look like what it does before it's touched. Signifiers — underline on a link, relief or border on a button, a cursor that changes — are the signals that communicate an element is actionable. A clickable element without signifiers exists but isn't discovered.
The Elements of Typographic Style
1 principleText legibility — measure and size
A line of running text reads well between 45 and 75 characters; longer, and the eye loses the line when returning, and shorter breaks the reading rhythm. Body text doesn't go below 16px on screen, and line spacing is around 1.5 times the font size.
The Magical Number Seven, Plus or Minus Two
1 principleMiller's Law — 7 plus or minus 2
Human working memory can hold 7 plus or minus 2 items at once. In navigation: no more than 7 items per level. Exceeding this limit increases cognitive load and choice errors.
Usability Testing Guide
1 principleUsability Test Planning
A usability testing plan should include: the test goal, 3 to 5 tasks based on real user flows, measurable success criteria per task, and a participant screener aligned with the personas.
User Flows in UX Design
1 principleUser Flow — Happy Path and Error Path
Every user flow should document the happy path (no errors) AND the error paths. Each flow needs: entry point, decision points, success states and error states.
User Research Methods
1 principleQualitative User Research
Qualitative interviews should explore behaviors, motivations and context of use, not opinions about solutions. Ask about past experiences, not hypothetical ones.
UX Metrics
1 principleUX Metrics Baseline Comparison
UX metrics only have comparative value. Always measure against an established baseline. Without a baseline, a 70% task completion rate says nothing.
UX Prototypes: Low Fidelity vs. High Fidelity
2 principlesLow-fidelity prototypes
Low-fidelity wireframes use minimal visuals, placeholder content and limited interactivity — they serve to iterate quickly and keep stakeholders focused on structure, not visual finish.
Mid-fidelity prototypes — Bridge to Hi-fi
A prototype's fidelity varies across several dimensions (visual, content, interactivity) independently — a mid-fidelity wireframe raises visual or content detail without yet reaching the full interactivity of a Hi-fi, and so validates hierarchy before investing in final polish.
Web Content Accessibility Guidelines 2.1 — Success Criterion 1.4.3
1 principleWCAG 2.1 — Color contrast 1.4.3
Normal text under 18pt: minimum ratio 4.5:1. Large text 18pt or above: minimum ratio 3:1. Level AA required.
Web Content Accessibility Guidelines 2.1 — Success Criterion 1.4.11
1 principleWCAG 2.1 — UI component contrast 1.4.11
User interface components and informative graphics must have a contrast ratio of at least 3:1 against adjacent colors.
Web Content Accessibility Guidelines 2.1 — Success Criterion 2.5.5
1 principleWCAG 2.1 — Touch target size 2.5.5
The minimum size of an interactive area is 44x44 CSS pixels. Apple HIG: 44pt. Material Design: 48dp. The touch area can be larger than the visual element.
What are the Principles of Design?
1 principleDesign principles — Definition and application
Design principles are the explicit, shared rules that guide design decisions on visibility, learning, perception and usability — without documented principles the team decides by individual taste instead of by consistent criteria.
Why You Only Need to Test with 5 Users
1 principleWhy 5 Users
With 5 users you discover roughly 85% of usability problems. It's better to run multiple small rounds of 5 users and iterate than one large round.