What is web accessibility?

An accessible site allows several ways of using it. The same page has to work with a screen reader, with text enlarged to 200 %, without a mouse, with captions switched on or with modified system colours. The limitation is not always permanent either: a temporary injury, a screen in bright sunlight or a noisy environment create very similar barriers for a while.

The international guidelines organise all their technical criteria under four principles.

• Perceivable: information must arrive through more than one sensory channel, so that someone who cannot see an image receives its description and someone who cannot hear a video can read its captions.
• Operable: the interface must be usable by keyboard, by voice or with an assistive device, without demanding precise gestures or rigid time limits.
• Understandable: the wording, the order of the steps and the error messages must be predictable and explain what has happened.
• Robust: the code must be interpreted reliably by browsers and assistive technologies, both current and future ones.

Each principle becomes concrete in verifiable success criteria, and each criterion carries a level. That is the part that can be audited and documented.

The technical reference is the Web Content Accessibility Guidelines, known as WCAG. The version in force is WCAG 2.2, published as a W3C Recommendation in October 2023 and updated in December 2024. Its criteria are spread across three conformance levels: A as the minimum, AA in the middle and AAA as the strictest. Legal texts usually rely on level AA, because AAA is not achievable for every kind of content.

In Europe, the normative translation of those guidelines is the harmonised standard EN 301 549 on accessibility requirements for ICT products and services, whose current version points to WCAG 2.1 at level AA.

The European Accessibility Act, Directive (EU) 2019/882, applies from 28 June 2025. It covers certain consumer products and services: e-commerce, consumer banking services, e-books, electronic communications services, access to audiovisual media services and digital elements of air, rail, waterborne and bus passenger transport. Spain transposed it through Ley 11/2023, whose Title I entered into force on that same date. Microenterprises providing services are exempt from those accessibility requirements; the law defines a microenterprise as one employing fewer than ten people with an annual turnover or annual balance sheet total not exceeding two million euros.

An earlier rule governs the Spanish public sector, Real Decreto 1112/2018, which requires publishing an accessibility statement and offering a feedback mechanism for complaints and suggestions. Whether a specific case falls within one scope or the other depends on the type of service, the recipient and the size of the organisation, and that assessment belongs to an individual legal review.

Something very concrete depends on accessibility: whether a person can complete a purchase, open an account or book an appointment without anyone's help. A form whose fields carry no associated label cannot be filled in with a screen reader, and at that point the transaction stops completely.

It also weighs on procurement decisions. Public tender documents include accessibility requirements, and large private tenders frequently ask for evidence of the level reached. An audit against verifiable criteria answers those questions with proof rather than with a statement of intent.

The link with SEO does exist, though it needs careful wording. Accessibility is not a ranking factor. What is true is that several practices overlap: alternative text describes an image for the screen reader and for the search engine alike, a correct heading hierarchy helps both grasp the structure of the document, and semantic markup makes the role of each element explicit. That overlap is real, and it makes accessibility work that is compatible with SEO rather than a ranking lever.

• Alternative text based on function: describe what the image contributes in its context. If it is decorative, an empty alt attribute keeps the screen reader from announcing it; if it is a link or a button, the alternative text describes the destination or the action.
• Sufficient contrast: level AA asks for a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text, plus 3:1 for the boundaries of user interface components and graphical objects.
• Full keyboard operation: walk through the site with the tab key. The focus must always be visible, follow a logical order and never get trapped inside menus, carousels or modal windows.
• Associated form labels: every field with a visible label linked through label and for. Errors are described in text, naming the field at fault and how to correct it, without relying on the colour red alone.
• A real heading hierarchy: one h1 per page and consecutive levels below it with no skips. Headings structure the document, and text size is decided in the stylesheet.
• Resizable text and alternatives for time-based media: content must stay readable and usable when text is enlarged to 200 %, videos need captions and audio needs a transcript.

• Generic alt attribute: values such as 'image', 'photo' or the file name take the place of the real description and carry no information.
• Low contrast on secondary elements: help text, placeholders inside input fields and disabled states often fall below the required minimum.
• Components built from div and span: tabs, dropdowns or checkboxes built without accessible roles, names and states tell an assistive device nothing, even when they work with a mouse.
• Focus removed for looks: switching off the focus outline with outline: none leaves keyboard users without a visual reference.
• Relying on automated checks alone: a validator detects a portion of the criteria, such as contrast or missing attributes. The rest requires manual testing, and a high tool score is not conformance.