WCAG 2.1 AA requirements explained in plain language

Key takeaways

• WCAG 2.1 Level AA contains 50 success criteria: 30 at Level A and 20 at Level AA, grouped under four principles. Content must be perceivable, operable and understandable, and it must work with assistive technology.
• It is the version courts, the Justice Department’s Title II rule and the HHS Section 504 rule point to, so it is the realistic target for most US organizations.
• WCAG 2.2, published by the W3C in 2023, keeps nearly all of 2.1 and adds nine new success criteria, six of them at Levels A and AA. Meeting 2.2 AA also meets 2.1 AA.
• Most failures come from a short list: the 2026 WebAIM Million report found low-contrast text on 83.9% of top home pages, followed by missing alt text and missing form labels.
• Automated scanners catch only part of the criteria, so keyboard and screen reader testing is required to confirm conformance.

The Web Content Accessibility Guidelines (WCAG) 2.1 AA standard is written for precision, not easy reading. This Emulent guide translates it into plain language: what each of the four principles asks for, the criteria that trip up most websites and how to check your own site. It is general guidance, not legal advice, and it summarizes the standard rather than replacing the official W3C specification.

What is WCAG 2.1 AA?

WCAG is the international technical standard for web accessibility, published by the World Wide Web Consortium (W3C). Version 2.1 came out in 2018 and added criteria for mobile devices, low vision and cognitive disabilities. Each success criterion has a level: A is the minimum, AA is the widely adopted target and AAA is the highest. “WCAG 2.1 AA” means meeting every Level A and Level AA criterion.

The standard is organized under four principles: perceivable, operable, understandable and a fourth covering compatibility with browsers and assistive technology. The sections below walk through each one in plain terms. The Justice Department’s 2024 Title II rule and the HHS Section 504 rule both adopt WCAG 2.1 AA, and both agencies pushed their compliance dates back by one year in 2026 without changing the standard.

What does “perceivable” mean in plain language?

People must be able to take in your content through at least one of their senses. If someone cannot see an image or hear a video, there needs to be another way to get the same information.

• Text alternatives: informative images need alt text that conveys their purpose; decorative images get empty alt text so screen readers skip them.
• Captions and transcripts: prerecorded video needs captions, prerecorded audio needs a transcript and live video needs live captions.
• Audio description: when a video shows important information that is not spoken, provide narration or a text alternative that describes it.
• Meaningful structure: headings, lists and tables must be coded as headings, lists and tables instead of only being styled to look that way.
• Color is not the only signal: a red border alone cannot be the only way to show a form error.
• Contrast: at least 4.5:1 for normal text, 3:1 for large text and 3:1 for icons, buttons and form borders.
• Resize and reflow: text can be enlarged to 200%, and content works at a 320-pixel width without scrolling sideways.
• Text spacing: content still works when users increase line height, letter spacing or word spacing.
• Hover content: tooltips and popups that appear on hover or focus can be dismissed, hovered over and stay visible until closed.

What does “operable” mean in plain language?

People must be able to use every part of your interface, whether they use a mouse, keyboard, switch device, voice control or touch screen.

• Keyboard access: everything works with a keyboard, and focus never gets trapped inside a widget.
• Visible focus: users can always see which element is selected.
• Logical focus order: tabbing moves through the page in an order that makes sense.
• Skip links: a way to bypass repeated navigation and jump to main content.
• Enough time: users can turn off, adjust or extend time limits, and can pause anything that moves, blinks or auto-updates.
• No seizure triggers: nothing flashes more than three times per second.
• Clear page titles and link text: each page has a descriptive title and each link’s purpose is clear from its text or context.
• Multiple ways to find pages: such as a menu plus search or a site map.
• Pointer gestures: anything that needs a swipe, pinch or drag also works with a single tap or click.
• Labels match names: the visible label on a button is included in its accessible name, so voice control users can say what they see.

What do “understandable” and “compatible” mean in plain language?

Understandable means people can read your content and predict how your interface behaves. The compatibility principle means your code works with browsers and assistive technologies, now and as they change.

To check your site against all four principles, run WAVE, axe DevTools or Google Lighthouse on your main templates, then test with only a keyboard and with a screen reader such as NVDA, VoiceOver or TalkBack. Scanners miss judgment calls like whether alt text is accurate or focus order makes sense. Skip overlay widgets as a shortcut; UsableNet counted more than 1,400 lawsuits in 2025 against companies that had them installed. Many of these fixes also support SEO, since alt text, headings and descriptive links help search engines and AI answer engines read your pages. On WordPress sites, most fixes happen at the template and element level.

How the Emulent team can help

Emulent audits websites against WCAG 2.1 AA and 2.2 AA, combining automated scans with manual keyboard and screen reader testing, and explains every finding in plain language your team can act on. Our website design team then fixes the issues in your templates and content and sets up checks so new pages stay compliant. To find out how your website measures up, contact the Emulent team.