design-usability-rules

Apply Nielsen's heuristics field by field: check for persistent labels above inputs, inline validation on blur, specific error messages with fix examples, and preserved user input after errors. The audit produces a checklist of violations with concrete remediation steps.

WCAG AA requires a minimum contrast ratio of 4.5:1 for body text and 3.0:1 for large text (18pt or larger, or 14pt bold). Contrast must be evaluated across all background surfaces, gradients, and interactive hover and focus states.

Interactive or data-bearing text such as buttons, labels, and table cells must be at least 11px. Body paragraphs should be at least 14px, with 16px preferred for sustained reading on high-DPI and mobile displays.

Validate on blur when the user leaves a field for format constraints, and on submit for cross-field logic. Never show errors while the user is mid-entry unless the input is unquestionably wrong, such as letters in a numeric-only field.

Touch targets must be at least 44x44px, with 48x48px ideal, to prevent fat-finger errors. Primary actions should sit in the thumb zone at the center and lower screen areas, avoiding top corners.

Do not use it as the primary guide for backend architecture, threat modeling, or release operations. It is scoped to UX architecture, visual hierarchy, responsiveness, and interface behavior evaluation.