TECHNICAL · SEO GLOSSARY
Web Accessibility (a11y)
The practice of building websites usable by people with disabilities — through semantic HTML, alt text, keyboard navigation, colour contrast, and ARIA — which overlaps significantly with SEO best practices.
Definition
Web accessibility (abbreviated a11y — "a" + 11 letters + "y") is the practice of ensuring websites are usable by people with visual, auditory, motor, or cognitive disabilities. The WCAG (Web Content Accessibility Guidelines) standard defines four principles: Perceivable (content is available to all senses), Operable (interface is navigable without a mouse), Understandable (content and controls are predictable), Robust (content works with assistive technologies). The accessibility–SEO overlap is substantial: alt text (accessibility) = image keyword signal (SEO); semantic heading hierarchy (accessibility screen readers) = content structure signal (SEO); descriptive link text like "read the full report" vs "click here" (accessibility) = internal link anchor text quality (SEO); keyboard-navigable focus management (accessibility) = Google's INP metric (SEO).
Why it matters for SEO
Accessibility compliance (WCAG AA) is increasingly a legal requirement in many jurisdictions (ADA in the US, EN 301 549 in the EU). Beyond compliance, accessibility improvements frequently produce direct SEO benefits: adding alt text to undescribed images is an accessibility fix and an on-page SEO win; improving heading hierarchy improves screen reader navigation and heading structure signals; fixing colour contrast issues has no SEO impact but pairs naturally with the same audit pass. Google also explicitly notes that accessible pages tend to perform better in Core Web Vitals — particularly INP and CLS — because accessibility improvements often require reducing DOM complexity and JavaScript event-handling overhead.
How DeepSEOAnalysis checks this
The audit checks the subset of accessibility issues that overlap with SEO: images missing alt text, images with empty alt text on non-decorative images, heading hierarchy violations (skipped heading levels, multiple H1s), links with non-descriptive text ("click here", "read more"), missing `lang` attribute on `<html>`, and `<meta name="viewport">` presence (required for mobile rendering and therefore Core Web Vitals). Full WCAG 2.1 AA compliance auditing is outside the scope of the SEO audit.
Useful tools and resources
GLOSSARY
Related terms
onpage
Alt Text (Image Alt Attribute)
A text description of an image, written in the HTML `alt` attribute — required for accessibility and used by search engines to understand image content.
Read definition →performance
Core Web Vitals
Three Google metrics — LCP, INP, and CLS — that measure real-user loading, interactivity, and visual stability.
Read definition →performance
INP (Interaction to Next Paint)
The Core Web Vital that measures a page's responsiveness to user interactions — replacing FID in March 2024 as a Google ranking signal. Good INP is under 200ms.
Read definition →technical
Mobile SEO
SEO considerations specific to mobile devices — covering mobile-first indexing, responsive design, tap target size, font legibility, Core Web Vitals on mobile, and ensuring no mobile-specific content is hidden from Googlebot.
Read definition →See how your site scores on Web Accessibility (a11y).
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