Web accessibility: WCAG guide for SEO

What is WCAG?

WCAG (Web Content Accessibility Guidelines) are the international web accessibility standards published by the W3C (World Wide Web Consortium). The current version is WCAG 2.2, published in October 2023. WCAG defines four fundamental principles: web content must be Perceivable, Operable, Understandable, and Robust (POUR).

WCAG defines three conformance levels: A (minimum), AA (recommended standard), and AAA (optimal). Level AA is the standard generally required by accessibility legislation worldwide, including the ADA (Americans with Disabilities Act) in the United States and the European Web Accessibility Directive. Most SEO-relevant criteria are covered by level AA.

In France and Canada, digital accessibility legislation requires WCAG AA compliance for public and many private sites. Non-compliance can result in legal sanctions and lawsuits. Beyond legal compliance, accessibility broadens your audience: approximately 15% of the world's population lives with a disability.

TeckBlaze integrates axe-core, the world's most widely used accessibility engine, to automatically check WCAG criteria on every audited page. Axe-core detects approximately 57% of accessibility issues automatically. Violations are classified by impact: critical, serious, moderate, and minor.

Color contrast

Color contrast is the most commonly failed accessibility check. WCAG AA requires a minimum contrast ratio of 4.5:1 between text and its background for normal text, and 3:1 for large text (18px bold or 24px regular). Level AAA requires 7:1 and 4.5:1 respectively.

Insufficient contrast makes text difficult or impossible to read for people with visual impairments, low vision, or in unfavorable lighting conditions (screen in sunlight). This affects millions of users, many of whom are not officially diagnosed.

TeckBlaze automatically detects contrast issues via the axe-core color-contrast rule. The report identifies each element with insufficient contrast, the current ratio, and the minimum required ratio. To fix, adjust either the text color or background color to reach the 4.5:1 ratio. Tools like WebAIM Contrast Checker allow quick ratio verification.

Contrast also indirectly affects SEO: hard-to-read text increases bounce rate and reduces time on page. Google measures these engagement signals in its ranking factors. Good contrast improves readability for all users, not just those with disabilities.

Alternative text (alt text)

The alt attribute on images is essential for both accessibility and SEO. Screen readers read alternative text aloud to describe images to blind or visually impaired users. Google also uses alt text to understand image content and display them in Google Images.

Every informative image must have a descriptive alt attribute that describes the image's content and function. Decorative images (that don't add information) should have an empty alt (alt="") so screen readers ignore them. Images that are also links should have alt text that describes the link destination.

TeckBlaze detects images without alt attributes and classifies them as medium severity. The detailed audit report lists each affected image with its source URL, dimensions, and context. Our engine also detects broken image sources (empty src, #, or about:blank).

For SEO-friendly alt text: describe the image in 5 to 15 words, include your primary keyword if natural, be specific ("TeckBlaze dashboard showing SEO score" rather than "image"), and avoid keyword stuffing. Don't start with "image of" or "photo of" — screen readers already announce it's an image.

ARIA and semantic structure

ARIA (Accessible Rich Internet Applications) is a set of HTML attributes that improve accessibility of dynamic web content and complex interface components. The most common ARIA attributes are role (defines an element's function), aria-label (provides an accessible label), aria-expanded (indicates if an element is expanded/collapsed), and aria-hidden (hides an element from screen readers).

The fundamental ARIA rule is: use native semantic HTML first before resorting to ARIA. A native <button> is always preferable to a <div role="button">. A <nav> is preferable to a <div role="navigation">. Semantic HTML is better supported, more robust, and requires less additional JavaScript for accessibility.

TeckBlaze detects invalid or contradictory ARIA attributes via axe-core. Common ARIA violations include: aria-hidden="true" on a focusable element, invalid or unrecognized role, aria-label on an element that doesn't support it, and aria-required without the corresponding HTML required attribute.

Semantic structure (correct use of <main>, <nav>, <header>, <footer>, <aside>, <section>) is also important for accessibility. Screen readers use these landmarks to allow users to quickly navigate between page sections. TeckBlaze checks that all content is within appropriate ARIA regions (landmarks).

Keyboard navigation

All interactive elements (links, buttons, form fields, menus) must be accessible and usable with keyboard alone, without a mouse. This is essential for screen reader users, users with motor impairments, and advanced users who prefer keyboard navigation.

Native HTML interactive elements (<a>, <button>, <input>, <select>) are naturally keyboard accessible. Problems arise when developers use <div> or <span> with onClick event handlers without adding corresponding keyboard accessibility (tabindex, onKeyDown, role).

The focus indicator (visible outline when an element is keyboard-selected) is crucial and must never be removed with CSS outline: none without providing a visible alternative. Many sites remove the outline for aesthetic reasons, making keyboard navigation impossible.

TeckBlaze detects non-keyboard-accessible interactive elements via corresponding axe-core rules. The report identifies elements needing tabindex, focusable but invisible elements, and links or buttons without accessible text.

Form labels and link text

Every form field (input, textarea, select) must have an associated HTML label via the for/id attribute or nesting. Screen readers read the label to inform users of the field's function. A field without a label is a mystery to blind users.

Links must have descriptive text that clearly indicates the destination. "Click here" or "Learn more" provides no information out of context. Screen readers often present a list of all page links — if 10 links all say "Learn more," users can't distinguish them.

For icon links (button with only an icon), add a descriptive aria-label: <button aria-label="Close menu"><CloseIcon /></button>. Without aria-label, the screen reader cannot announce the button's function.

TeckBlaze checks for form labels and link text quality via axe-core rules label, link-name, and button-name. Violations are classified as serious because they prevent effective use of forms and navigation.

Accessibility impact on SEO

Accessibility and SEO share many common objectives. Image alt text helps both screen readers and Google Images. Heading hierarchy (H1-H6) helps screen readers navigate and Google understand content structure. Semantic HTML benefits assistive technologies and Google crawlers.

The Lighthouse accessibility score is integrated into TeckBlaze's UX score, which represents 15% of the overall SEO score. The UX score is calculated as the average of Lighthouse accessibility and best practices. A site with an accessibility score of 50 significantly penalizes its overall SEO score.

Google has confirmed that accessibility is not a direct ranking factor, but accessibility practices improve many indirect ranking signals: time on site (readable content), bounce rate (clear navigation), mobile compatibility (responsive design), and content structure (semantic HTML).

Moreover, with the emergence of GEO (Generative Engine Optimization), semantic structure and accessibility become even more important. AI models use semantic HTML and ARIA attributes to understand content context and structure. An accessible site is better understood by humans, search engines, and AI models.

WCAG contrast levels

FAQ