Category: Visual and Media Accessibility

Alternative Text

Also known as: Alt Text, Alt Text, Alt Attribute, Text Alternative

Simply put

Alternative text, commonly called alt text, is descriptive text that conveys the meaning and context of an image or other visual content in a digital setting, such as a web page or app. It allows people who cannot see the image, such as those using screen readers, to understand the information the visual is meant to communicate. Providing alt text is generally considered an essential part of making digital content accessible.

Formal definition

Alternative text is a textual substitute for non-text content, most commonly images, in digital content. Its purpose is to convey the meaning, function, or context of the visual item rather than merely to label its presence, so that assistive technologies such as screen readers can present an equivalent experience to users who cannot perceive the image. Effective alt text is concise and context-dependent: the appropriate description varies with how the image is used, and purely decorative images are generally handled differently (for example, marked so assistive technology can skip them). Text alternatives are a core concept underlying WCAG Success Criterion 1.1.1 Non-text Content (Level A), though this entry does not restate the criterion's full requirements.

Why it matters

Alternative text is one of the foundational elements of digital accessibility because so much online information is communicated visually. When an image conveys meaning, function, or context, people who cannot perceive that image, such as those using screen readers, depend on a text alternative to receive an equivalent understanding. Without alt text, a photo, chart, icon, or button image may be announced only as an unlabeled graphic or skipped entirely, leaving the user with an incomplete or confusing experience.

Alt text also supports the core goal of providing an equivalent experience rather than simply flagging that an image exists. Recognized authorities, including Section508.gov, WebAIM, and Harvard's accessibility guidance, describe text alternatives as an essential part of making digital content accessible. Because the concept underlies WCAG Success Criterion 1.1.1 Non-text Content (Level A), it is commonly among the first things evaluated in accessibility reviews, and missing or poor alt text is a frequently cited barrier.

Who it's relevant to

Content authors and editors

Anyone who adds images to web pages, documents, or apps is generally responsible for supplying appropriate alt text. Because the right description depends on how an image is used, authors are usually best positioned to judge whether an image is informative, functional, or decorative and to describe it accordingly.

UX designers and developers

Designers and developers shape how images are implemented and how alt text is captured and rendered. They help ensure that content management systems and interfaces prompt for text alternatives, that decorative images can be marked so assistive technology skips them, and that alt text is correctly exposed to screen readers.

Accessibility and compliance teams

Those evaluating conformance often review alt text early, since text alternatives underlie WCAG Success Criterion 1.1.1 Non-text Content (Level A). Because automated tools can detect a missing alt attribute but generally cannot judge whether the text is meaningful or appropriate, manual review and assistive technology testing are typically required.

Users of assistive technology

People who use screen readers or otherwise cannot perceive images rely directly on alt text to understand visual content. Well-written text alternatives give these users an experience equivalent to that of sighted users, while missing or poor alt text can leave them without key information.

Inside Alt Text

Text Alternative

A concise textual description of a non-text element, most commonly provided via the alt attribute on HTML img elements, that conveys the meaning or function the image serves in its context.

Function versus Decoration

A distinction between images that carry meaning or serve a function (which require descriptive alternative text) and purely decorative images (which are generally given an empty alt attribute so assistive technologies can skip them).

Contextual Relevance

The requirement that the description reflect the image's purpose within the surrounding content, since the same image may warrant different alternative text depending on how it is used.

Functional Text for Actionable Images

For images used as links or controls, alternative text that describes the destination or action rather than the image's appearance.

Relationship to WCAG

Alternative text is the primary technique associated with WCAG Success Criterion 1.1.1 Non-text Content, a Level A criterion present since WCAG 2.0, which calls for text alternatives that serve an equivalent purpose.

Common questions

Answers to the questions practitioners most commonly ask about Alt Text.

Does every image on a page need alternative text?

No. Images that are purely decorative and convey no meaningful information should be given an empty alt attribute (alt="") so that assistive technologies can skip them. Adding descriptive text to decorative images can create unnecessary noise for screen reader users. The goal is to convey the information or function an image provides, not to describe every image regardless of purpose.

Is adding alternative text enough to make a page accessible or WCAG-conformant?

No. Alt text addresses text alternatives for non-text content, which relates to specific WCAG success criteria, but accessibility depends on many other factors such as keyboard operability, color contrast, structure, and more. Providing alt text is one necessary practice among many. Meeting a single requirement does not guarantee overall conformance, an accessible experience for all users, or immunity from legal claims. Manual and assistive technology testing are generally required in addition to automated checks, which detect only a portion of issues.

How long should alternative text be?

Alt text should be concise while conveying the meaning or function the image provides in its context. There is no fixed character limit in the standards, but overly long descriptions are commonly discouraged for the alt attribute itself. When an image requires a longer explanation, such as a complex chart, the detailed description is often placed in adjacent text or another accessible mechanism, with the alt attribute providing a brief summary.

What alt text should be used for images that are also links or buttons?

When an image functions as a link or a control, the text alternative should generally describe the destination or action rather than the image's appearance. For example, an image acting as a link to a home page is often better described by its function than by a literal description of the graphic, so that users understand what activating it will do.

How should alternative text be handled for images that contain text?

When an image contains text that conveys information, the alt text should generally include that text so it is available to assistive technology users. Keep in mind that WCAG also addresses images of text separately, and using actual text instead of images of text is commonly recommended where feasible.

What is the difference between an empty alt attribute and a missing alt attribute?

An empty alt attribute (alt="") explicitly marks an image as decorative, signaling assistive technologies to ignore it. A missing alt attribute is different: many screen readers may fall back to announcing the file name or other unhelpful information. For this reason, decorative images should use an intentional empty alt attribute rather than omitting the attribute entirely.

Common misconceptions

Every image on a page must have descriptive alternative text.

Purely decorative images generally should have an empty alt attribute so that assistive technologies ignore them; forcing descriptions onto decorative images can add noise for screen reader users. Whether an image is decorative depends on its role in context.

Providing alternative text guarantees WCAG conformance and legal compliance.

Alternative text addresses one Level A success criterion and does not by itself ensure full accessibility or immunity from legal claims. Conformance requires meeting many other criteria, and manual and assistive technology testing are needed beyond automated checks. This is not legal advice.

Automated tools can fully verify that alternative text is correct.

Automated testing can detect whether an alt attribute is present or missing, but it cannot reliably judge whether the text is meaningful, accurate, or appropriate for the context. Human review is generally required to confirm quality.

Best practices

Write alternative text that conveys the image's meaning or function in its specific context rather than simply describing its visual appearance.

Use an empty alt attribute for purely decorative images so that assistive technologies can skip them.

For images that act as links or controls, describe the destination or action rather than the graphic itself.

Keep descriptions concise while including the information a user would otherwise miss, and consider a longer description elsewhere on the page when an image conveys complex information.

Review alternative text manually and test with assistive technologies, since automated tools can confirm presence but not appropriateness or accuracy.

Reassess alternative text when the same image is reused, because the appropriate description may change with the surrounding content and purpose.