Web Accessibility: Complete Definition and Guide

What is web accessibility?

Web accessibility (often abbreviated a11y, for the 11 letters between the "a" and "y" of "accessibility") refers to the practice of designing and developing websites and applications so they can be used by the widest possible range of people, regardless of their physical, sensory or cognitive abilities. This includes visually impaired users who rely on screen readers, deaf users who need captions, users with motor impairments who navigate by keyboard, and users with cognitive disabilities who benefit from simplified interfaces.

Web accessibility is not an add-on feature: it is a fundamental right recognised by the United Nations Convention on the Rights of Persons with Disabilities and governed by national and European legislation. In Belgium, the European directive on the accessibility of websites and mobile applications of public sector bodies (Directive 2016/2102) imposes strict standards.

At KERN-IT, the KERNWEB division integrates accessibility from the design phase of every project. Our Figma mockups include contrast checks, our TailwindCSS code follows WCAG standards, and Wagtail CMS enables editors to provide the alternative text and descriptions necessary for accessibility.

Why web accessibility matters

Beyond the ethical and legal obligation, web accessibility offers significant strategic benefits for businesses.

• Wider audience: approximately 15 % of the global population lives with some form of disability. Making a site accessible opens it to millions of additional users.
• SEO improvement: accessibility practices (semantic HTML, alternative text, logical heading structure) directly benefit search ranking. Google rewards accessible sites.
• Better experience for everyone: an accessible site is better designed for all users. Captions help people in noisy environments, keyboard navigation aids power users, and high contrast improves readability in sunlight.
• Legal compliance: European legislation (European Accessibility Act, applicable from 2025) extends accessibility obligations to the private sector. Non-compliant businesses face sanctions.
• Social responsibility: web accessibility demonstrates a concrete commitment to inclusion and diversity, values increasingly valued by clients and partners.

How it works

Web accessibility is structured by WCAG (Web Content Accessibility Guidelines), the international guidelines published by the W3C. WCAG defines four fundamental principles, summarised by the acronym POUR.

Perceivable: content must be presentable in ways that all users can perceive. This means providing alternative text for images, captions for videos, audio descriptions for multimedia content and sufficient colour contrast (minimum 4.5:1 ratio for normal text).

Operable: interface components and navigation must be operable by everyone. All functionality must be keyboard-accessible, users must have enough time to read and interact, and content must not cause seizures (no excessive flashing).

Understandable: content and interface operation must be comprehensible. Text must be readable and predictable, forms must provide clear instructions and explicit error messages.

Robust: content must be robust enough to be reliably interpreted by a wide range of assistive technologies (screen readers, magnifiers, voice controls). This requires valid, semantic HTML markup and correct use of ARIA roles.

Concrete example

The KERNWEB team at KERN-IT conducts an accessibility audit of a Belgian institutional website built on Wagtail CMS. The site must achieve WCAG 2.1 AA compliance to meet European legislation.

The audit reveals several issues: images without alternative text, forms without explicit labels, insufficient contrast on secondary buttons, impossible keyboard navigation in the mobile menu, and videos without captions. Each issue is documented with its location, severity and recommended fix.

Fixes are implemented progressively: adding a mandatory alt field in Wagtail StreamField image blocks, updating the TailwindCSS configuration to ensure compliant contrast ratios, refactoring the mobile menu with correct keyboard focus management and ARIA attributes, and integrating an accessible video player with captioning.

After corrections, the site achieves a Lighthouse accessibility score of 96 and passes a manual audit conducted with the NVDA screen reader.

Implementation steps

1. Audit the current state: conduct an accessibility audit combining automated tools (Lighthouse, axe DevTools) with manual testing (keyboard navigation, screen reader).
2. Train the team: educate designers, developers and content editors on WCAG principles and accessibility best practices.
3. Design for accessibility: integrate accessibility from the Figma design phase: check contrasts, plan focus states and structure the heading hierarchy.
4. Develop accessibly: use semantic HTML, implement ARIA roles correctly, ensure keyboard navigation and test with assistive technologies.
5. Configure the CMS: in Wagtail, make alt fields mandatory, provide guidelines for editors and configure StreamField blocks to encourage best practices.
6. Test continuously: integrate accessibility tests into the CI/CD pipeline and conduct regular manual audits.
7. Document and maintain: write an accessibility statement, set up a reporting channel and maintain compliance over time.

Related technologies and tools

• Lighthouse: a Google tool built into Chrome that provides an accessibility score and automatically identifies common issues.
• axe DevTools: a browser extension by Deque Systems that detects accessibility violations directly in the developer tools.
• Wagtail CMS: the Django CMS used by KERN-IT, offering built-in accessibility features (alt text, semantic structure) and an admin interface that is itself accessible.
• Tailwind CSS: a CSS framework that simplifies contrast management, font sizing and focus states via its utility classes.
• NVDA / VoiceOver: free screen readers (Windows / macOS) used to manually test a site's accessibility.

Conclusion

Web accessibility is not a technical constraint: it is a commitment to an inclusive web usable by all. The benefits go well beyond legal compliance: an accessible site is a better-designed, better-indexed site open to a wider audience. At KERN-IT, the KERNWEB division integrates accessibility at every phase of its projects, from Figma design to Tailwind CSS development to Wagtail CMS configuration, ensuring every delivered site meets WCAG standards.