Web Content Accessibility Guidelines (WCAG) 2 

Web Content Accessibility Guidelines (WCAG) 2, built on WCAG 1 and published on 11 December 2008, are international standards created by the World Wide Web Consortium (W3C).

It is primarily designed for web content developers, web accessibility evaluation tool developers, web authoring tool developers, and anyone who wants to ensure their web content meets accessibility standards, including mobile devices. 

This ISO-standard-approved version provides guidelines that make websites and web applications usable and inclusive for all users, regardless of their abilities, including people with disabilities.

WCAG 2 covers a wide range of guidelines organized under four principles: perceivable, operable, understandable, and robust. These principles are further divided into 12 guidelines and testable success criteria at three levels: A, AA, and AAA. The success criteria determine whether a website or web application conforms to WCAG standards.

Principles of Accessibility

WCAG 2 is built around four key principles that ensure web content is accessible to everyone: Perceivable, Operable, Understandable, and Robust.

Perceivable

The “Perceivable” principle of WCAG 2 ensures that web content is presented in a way that can be perceived by all users, regardless of their abilities. It means that the information on a website or app must be available to users through at least one of their senses, such as sight, hearing, or touch.

Examples of perceivable design include providing text alternatives for non-text content like images, video captions, and audio transcripts. Additionally, the text and background colors should have sufficient contrast to be easily readable.

Operable

Another key principle of WCAG 2 is operability. It’s like a website’s smooth navigation system, which allows users to interact with it easily. When we say operable, we mean that users must be able to operate and navigate the interface without any barriers.

For example, operable content ensures that everyone can access and utilize it, no matter how they choose to do so. This includes making sure that keyboard-only users can navigate through web features smoothly.

It also means using descriptive links that clearly indicate where they lead and what content they contain.

Understandable

The “Understandable” principle focuses on making web content and user interfaces accessible and easy to comprehend. It ensures users understand the information presented and how to operate the website or app. Key examples are:

• Writing content in clear language

• Marking any language changes

• Keeping features consistent and intuitive

• Labeling form fields clearly

Robust

Robust is like creating content that can withstand any challenge and can be reliably interpreted by users, regardless of how they access it.

For example, robust involves ensuring that your code is compatible and readable by assistive technologies. It also means that your content uses HTML to ensure that user agents and assistive technologies can accurately interpret the digital content.

Moreover, essential status messages or dialogues should be marked to inform users of their presence and purpose, allowing seamless interaction with assistive technologies.

Guidelines and Success Criteria

Under the four main principles of WCAG 2, 12 specific guidelines provide goals for authors to achieve. These guidelines explain how to make content more usable for users with different disabilities. The guidelines themselves cannot be tested directly.

However, each guideline has a testable success criterion. These criteria define the requirements for websites and apps to conform to WCAG 2 standards. They are classified into three levels of conformance: A (lowest), AA, and AAA (highest).

The success criteria allow WCAG 2 to be used for testing, purchasing, regulations, and legal requirements. Different conformance levels address varied user needs and situations. Following the guidelines and meeting success criteria ensures an accessible online experience for all.

Perceivable

The “Perceivable” principle in WCAG 2 provides four specific guidelines for making web content perceivable by all users. These guidelines focus on text alternatives, time-based media, adaptable content, and distinguishable content. Each guideline has a success criterion that should or must be met.

Text Alternatives

All non-text content that is presented to the user has a text alternative that serves the equivalent purpose, except for the situations listed below:

Controls, Input

If non-text content is a control or accepts user input, it must have a name describing its purpose.

Test

If non-text content is crucial for an exercise or test and cannot be accurately represented in text, text alternatives should describe the content. It ensures accessibility without compromising the validity of the exercise or test.

Non-Text Time-Based Media

If the content isn’t text but is time-based media, then the text alternatives should describe what the non-text content is.

CAPTCHA

When non-text content aims to confirm human access, provide text alternatives that identify its purpose and offer alternative CAPTCHA forms using various sensory modes to accommodate disabilities.

Sensory

If non-text content is to convey a particular sensory experience, it should have text alternatives that describe the content in detail.

Decoration, Formatting, Invisible

If non-text content is pure decoration, used only for visual formatting, or not presented to users, it must be implemented in a way that assistive technology can ignore.

In summary, all non-text content needs a text alternative unless it falls under one of those exceptions, in which case it still needs at least a basic text identification. This is a Level A (minimum) requirement.

Time-Based Media

Time-based media refers to audio and video content presented over a specific duration. It is important to provide alternatives for time-based media to ensure everyone, including individuals with disabilities, can perceive and understand the information being conveyed.

When it comes to prerecorded audio-only and video-only media, there are specific rules to follow based on the level of success criteria:

Level A 

• Prerecorded Video-only: Offer an alternative for time-based media or an audio track that conveys the same information as pre-recorded video-only content.

• Prerecorded Audio-only: Provide an alternative that presents equivalent information for prerecorded audio-only content.

• Captions (Prerecorded): Ensure that all prerecorded audio content in synchronized media has captions unless the media serves as an alternative for text and is identified as such.

Level AA 

• Audio Description (Prerecorded): Provide audio description for all prerecorded video content in synchronized media.

• Captions (Live): Provide captions for all live audio content in synchronized media.

Level AAA 

• Sign Language (Prerecorded): Provide sign language interpretation for all prerecorded audio content in synchronized media.

• Extended Audio Description (Prerecorded): Provide extended audio description for prerecorded video content in synchronized media when pauses in foreground audio are insufficient.

• Media Alternative (Prerecorded): Provide an alternative for time-based media for all prerecorded synchronized media and video-only media.

• Audio-only (Live): Provide an alternative that presents equivalent information for live audio-only content.

Adaptable Content

The Adaptable guideline focuses on creating content that can be presented differently without losing its information or structure. This ensures that individuals with diverse needs and preferences can access and understand the content in a way that best suits them.

To meet the Level A success criteria under the Adaptable guideline, the following should be considered:

Info and Relationships

Ensure that information, structure, and relationships conveyed through content presentation can be programmatically determined or available in text. This allows assistive technologies to access and present the content accurately.

Sensory Characteristics

Understanding and operating content instructions should not depend solely on sensory characteristics such as shape, visual location, orientation, size, or sound. It ensures that individuals with sensory disabilities or limitations can still comprehend and interact with the content effectively.

Meaningful Sequence

When the sequence in which content is presented affects its meaning, ensure that a correct reading sequence can be programmatically determined. This helps individuals who rely on assistive technologies to understand the content in the intended order.

Distinguishable Content

The last guideline under the principle of being perceivable is having distinguishable content. This guideline focuses on making web content easier for all users to see and hear.

To meet the Level A success criteria under the Distinguishable guideline, consider the following:

Use of Color

Color should not be the sole means of conveying information, indicating actions, prompting responses, or distinguishing visual elements. It ensures that individuals with difficulty perceiving color can still understand and interact with the content effectively.

Audio Control

Suppose any audio on a web page plays automatically for more than three seconds. In that case, mechanisms should be available to pause or stop the audio or control the audio volume independently from the overall system volume level. It allows users to control audio playback and adjust it according to their preferences.

To achieve Level AA success criteria, consider the following additional factors:

Resize Text

Except for captions and images of text, text should be resizable up to 200% without loss of content or functionality without assistive technology. It ensures that users can adjust the text size according to their needs.

Images of Text

Whenever possible, convey information using text instead of images. However, there are exceptions where using images instead of text is allowed. For example, in some design contexts, using specific fonts or graphical treatments may be essential to convey a particular message or maintain branding consistency.

Contrast (Minimum)

The visual presentation of text and images of text should have a contrast ratio of at least 4.5:1, except for specific cases such as large-scale text or incidental text that doesn’t require a contrast requirement.

To attain Level AAA success criteria, you should consider the following additional factors:

Contrast (Enhanced)

The visual presentation of text and images of text should have a contrast ratio of at least 7:1, except for specific cases such as large-scale text or incidental text.

Visual Presentation

For blocks of text, users should be able to:

• Select foreground and background colors

• Limit the width  

• Justify the text 

• Provide appropriate line and paragraph spacing 

Low or No Background Audio

For prerecorded audio-only content, speech in the foreground should primarily be without background sounds, or users should have the option to turn off background sounds, or background sounds should be at least 20 decibels lower than the foreground speech content.

Images of Text (No Exception)

Text images should only be used for pure decoration or when a particular text presentation is essential to convey information. Logotypes are considered crucial.

Following these criteria or requirements helps users with vision impairments, like color blindness, perceive visual information beyond color distinctions. For hearing impairments, audio controls prevent disruptive automatic sounds.

Operable

The “Operable” principle in WCAG 2 outlines four guidelines for ensuring web content is operable by all users. These guidelines cover keyboard access, timing, avoidance of seizures and physical reactions, and navigability. Each guideline includes a success criterion that must be met for accessibility compliance.

Keyboard Access

The Keyboard Access guideline in the “Operable” principle of WCAG 2 ensures that people can easily navigate and interact with websites using only a keyboard. This is important because some individuals may have difficulty using a mouse or other pointing devices.

At Level A, the guideline requires that all website functionality be accessible through the keyboard without specific timing requirements for keystrokes. However, there are exceptions when the underlying function relies on the user’s movement path rather than endpoints.

For example, if you’re using handwriting to enter text, the handwriting requires a specific path, but the underlying function of text input does not. Additional input methods like a mouse are encouraged alongside keyboard access.

Another Level A success criterion is the “No Keyboard Trap” rule. It ensures that if users can move keyboard focus to a component (like a button or form field), they can also navigate away from it using only the keyboard.

Users must be informed of the alternative method if it requires more than standard methods like arrow keys or tab keys. This prevents users from getting stuck and unable to move around the website.

At Level AAA, the guideline requires that all website functionality be operable through the keyboard without specific timing requirements for keystrokes. This means every interactive element and action on the website should be accessible using the keyboard alone.

Enough Time

The Enough Time guideline in the “Operable” principle of WCAG 2 ensures that users have sufficient time to read and use a website’s content. 

At Level A, the Timing Adjustable criterion requires that if the content sets time limits, at least one of the following conditions must be met:

• Users can turn off the time limit before encountering it

• Users can adjust the time limit over a wide range

• Users are warned before time expires and allowed to extend the time limit

• There are specific exceptions where the time limit is essential or longer than 20 hours

The Pause, Stop, Hide criterion, also at Level A, focuses on moving, blinking, scrolling, or auto-updating information. It requires that if such content automatically starts, lasts over five seconds, and appears with other content, users must have a way to pause, stop, or hide it unless the movement or updates are vital to the activity.

At Level AAA, the No Timing criterion states that timing should not be an essential part of the event or activity presented by the content, except for non-interactive synchronized media and real-time events.

Additionally, interruptions should be postponable or suppressible by the user, except for emergencies. Finally, users should resume their activity without data loss after re-authenticating when an authenticated session expires.

Seizures and Physical Reactions

The “Operable” principle of WCAG 2 includes the Seizures and Physical Reactions guideline, which ensures that website content doesn’t trigger seizures or physical reactions. It is crucial for people prone to seizures or with photosensitive epilepsy.

Level A includes the “Three Flashes or Below Threshold” criterion, which limits flashing on web pages to three times per second or below specific thresholds for general and red flashes. It helps prevent the occurrence of seizures caused by flashing content.

At Level AAA, the Three Flashes criterion requires that web pages not contain anything that flashes more than three times in any second. This stricter criterion further reduces the risk of triggering seizures or physical reactions.

Navigability

Navigability is crucial to making websites accessible and easy to use for everyone. By the “Operable” principle of WCAG 2, the Navigability guideline provides tools and features that help users move around, find what they need, and understand where they are on a website.

Here are the success criteria for each level:

Level A

• Page Titled: Web pages must have descriptive titles, aiding users in understanding each page’s topic or purpose, especially with assistive technologies.

• Bypass Blocks: Users can skip repeated content blocks on multiple pages, saving time and avoiding redundancy.

• Focus Order: Focusable components are logically ordered for efficient navigation and meaningful interaction with content.

• Link Purpose (In Context): Link purposes are clear from the link text alone or with its context, reducing user ambiguity.

Level AA

• Multiple Ways: More than one navigation method should be available, except for specific processes, which enhance accessibility and user experience.

• Headings and Labels: Clear headings and labels describe the content, which improves understanding of its structure and organization.

• Focus Visible: Keyboard-operable interfaces show a visible focus indicator, which aids navigation for keyboard users.

Level AAA

• Location: Provide information about the user’s location within the website, aiding navigation efficiency.

• Link Purpose (Link Only): Links should have clear purposes discernible from the link text alone, reducing ambiguity.

• Section Headings: Organize content with headings for more straightforward navigation and comprehension.

Understandable

The “Understandable” principle in WCAG 2 includes three guidelines for making web content understandable for all users. The guidelines cover content readability, predictability, and input assistance.

Readability

This guideline aims to ensure that text content is readable and comprehensible. 

At Level A, websites must clearly show the main language used on each page. This helps computers understand the language automatically.

Moving to Level AA, websites must also identify the language of different sections or phrases. However, proper names and technical terms don’t need to be specified in a language.

Websites advancing to Level AAA should explain unusual words, phrases, idioms, and jargon. This helps users understand uncommon terms.

They should also explain abbreviations and acronyms. This allows for clarity when reading shortened forms.

Furthermore, websites must provide simpler content for text above a middle school reading level to ensure it is accessible to more users.

Finally, they should indicate how to pronounce words with multiple pronunciations. This clarifies ambiguous words based on their pronunciation.

Predictability

Predictability ensures that web pages behave consistently and as expected. This enhances usability and prevents user confusion.

At Level A, the “On Input” criterion states that a setting should not automatically trigger a context change unless the user is informed beforehand about this behavior.

Also, at Level A, the “On Focus” criterion requires that when a component receives focus, it does not unexpectedly change the context. This avoids disorienting the user.

Moving at Level AA, the “Consistent Identification” criterion requires that components with the same functionality are identified consistently throughout the website.

At Level AA, the “Consistent Navigation” criterion requires repeated navigation elements to maintain the same order across multiple pages unless the user makes a change.

Finally, at Level AAA, the “Change on Request” criterion ensures that context changes occur only upon user request or can be disabled if unwanted.

Input Assistance

The Input Assistance guideline in the “Understandable” principle of WCAG 2 focuses on helping users avoid and correct mistakes while interacting with web content.

At Level A, if a website detects an error in user input, it must identify the error and explain it in text. This helps users understand and fix their mistakes. At this level, websites must provide clear instructions or labels when asking users for input.

At Level AA, if a website can suggest corrections for an error, it should provide those suggestions to the user. However, it cannot compromise security or the purpose of the content.

At this level, websites must enable users to undo submissions, review information before submission, or check for errors before submitting, especially for tasks like: 

• Financial transactions

• Legal agreements

• Data modification

At Level AAA, websites should offer context-sensitive help when users need extra guidance. At this top level, websites must meet at least one of the conditions mentioned earlier regarding undoing, error checking, or reviewing information for any user input submission.

Robust

The “Robust” principle in WCAG 2 focuses solely on compatibility. It aims to ensure that web content works well with different devices and assistive technologies.

At Level A, websites using coding languages like HTML must follow the rules below to allow browsers to understand the code:

• Start and end tags must match

• Tags must be nested correctly

• IDs must be unique

• Attributes cannot be duplicated

At this exact level, all interactive components on a website must have names and roles that a computer can identify. This includes buttons, links, and form fields. 

Users must also be able to set properties like values or states. Note that assistive technologies need to be notified of any changes.

Levels of Conformance

WCAG 2.0 categorizes conformance into three levels, each showing how accessible a web page is.

Level A Conformance

This is the minimum level for a website to follow WCAG guidelines. At Level A, the website must meet all Level A Success Criteria. Or, it can provide an alternate version that meets Level A.

Level AA Conformance

The website needs to meet all Level A and Level AA Success Criteria at Level AA. It can also provide an alternate AA version instead.

Level AAA Conformance

Level AAA is the highest conformance level. Websites at this level must satisfy all Level A, AA, and AAA Success Criteria. Or offer an alternate AAA version.

While websites should aim high, some content may not be able to fully conform to Level AAA. So, Level AAA conformance for an entire site is only sometimes recommended as a broad requirement.

Websites are encouraged to work toward and report progress toward meeting higher-level criteria, even if full conformance has yet to be achieved.

Conformance only applies to complete web pages. If part of a page is excluded, it cannot conform. However, alternate content directly linked from the page counts as part of the page.

Suppose a website can’t conform due to reasons outside the author’s control, like language limitations. In that case, they can provide a “Partial Conformance Statement” explaining which levels they’d meet if those issues were resolved.

Claims of Conformance

Conformance to WCAG guidelines applies only to web pages. However, a claim can cover a single page, a group of related pages, or an entire website.

Making a conformance claim is optional. Websites can follow WCAG 2.0 without officially claiming it. But if a claim is made, it must include specific information:

• The claim date

• The conformance level met

• The specific guidelines version “Web Content Accessibility Guidelines 2.0“)

• The web technologies used on those pages

• A clear description of the pages included (list of URLs or other way to identify them)

For websites without URLs before installation, the claim can state it will conform once installed on the customer’s system.

If you use an official WCAG conformance logo, you are making a claim. So, the logo usage must include all the required information listed above.

Conformance claims help clarify which accessibility guidelines a website follows and for what pages. This transparency makes it easier for users to understand the site’s level of accessibility.

Additional Components of a Conformance Claim

When making a conformance claim for web accessibility, providing extra information to assist users is helpful. Here are some recommended additional components:

List of Met Success Criteria

Include a list of success criteria that have been met beyond the level of conformance claimed. This list should be in a format that users can easily understand, preferably in machine-readable metadata.

User-Agents and Assistive Technologies

Provide a list of user agents and assistive technologies used to test the content’s accessibility. This information helps users understand the content’s compatibility with different tools.

“Used but Not Relied Upon” Technologies

List the specific technologies used in creating the web content that are not essential for accessibility.

Machine-Readable Metadata

Create a machine-readable metadata version of the list of relied-upon technologies and the conformance claim itself. This allows automated tools to process and analyze the information more effectively.

Extra Steps for Accessibility

Share any additional measures taken to enhance the accessibility of the content beyond the required success criteria. This demonstrates a commitment to going above and beyond for accessibility.

For more details and examples of conformance claims, refer to the resource “Understanding Conformance Claims.” To learn more about the use of metadata in conformance claims, consult the resource “Understanding Metadata.”

Techniques for Meeting Each Success Criterion

Within WCAG 2, there are 61 success criteria spread across the 12 guidelines that focus on accessibility principles. To ensure compliance with these criteria, various techniques can be employed.

For example, sufficient techniques can be employed for non-text content at Level A, such as using aria-label to provide labels for objects and combining adjacent image and text links for the same resource.

Using an aria-label provides a label for objects that assistive technologies can read. Adding the aria-label attribute to an object, like a button, makes the text label available for screen readers to announce, which ensures that users understand the object’s purpose.

Another technique is to combine adjacent image and text links for the same resource. By providing both text and iconic representations of links, the web page becomes more accessible to keyboard users and assistive technology users. 

This approach caters to different user preferences. Some find text more usable, while others prefer icons, enhancing the link’s overall accessibility.

Regarding color usage at Level A, an advisory technique is to use CSS to modify the appearance of a user interface component when it receives focus. This technique highlights the element that has focus or is being hovered over, which provides valuable information such as interactivity or the element’s scope.

Meanwhile, a helpful technique at Level A for page titles is to show how the current page relates to others in the collection or site. You can do this programmatically with the rel attribute in HTML links or by including relevant info in the page’s title.

To explore an extensive list of techniques for meeting each criterion within the 12 guidelines of WCAG 2, you can refer to the “How to Meet WCAG (Quick Reference)” page, which provides comprehensive information.

Understanding Technology-Specific Techniques

The specific techniques for meeting criteria can depend on the website’s technologies, such as HTML, PDF, Flash, etc.

To learn more about technology-specific techniques related to WCAG 2, explore the “Understanding WCAG 2.0” page. It explains accessibility guidelines and how to comply with them using different technologies.

By exploring the provided techniques and understanding technology-specific strategies, you can improve web accessibility for all users.