Does every image need alt text?

No. In general, images that communicate important information or perform a function need alt text. Purely decorative images should typically use an empty alt attribute.

How long should alt text be?

There is no single required length. Simpler images may only need a few words, while more complex visuals may need additional explanation elsewhere on the page. Some guidance refers to roughly 70-140 characters as a practical "sweet spot" for writing alt text.

Does alt text help with SEO?

Yes. Search engines can use alt text, in tandem with surrounding page content, to better understand an image.

What is the difference between alt text and an image caption?

Alt text is primarily used to provide a text alternative for an image, while a caption is visible text displayed alongside an image on a webpage and is intended for all users. In some cases, they may communicate similar information, but they generally serve different purposes.

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Alt Text Best Practices: Accessibility, SEO, and WCAG

Samantha Mulkey

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October 14, 2026

Alt text is descriptive text added to an image though the HTML alt attribute that provides a written alternative when the visual itself cannot be seen or interpreted. It is used to describe an image for screen readers and search engines and may appear when an image fails to load. Alt text aids in making visual content accessible by communicating the purpose or meaning of an image to users who may not be able to see it. This is reflected in the Web Content Accessibility Guidelines (WCAG), which require non-text content to have a text alternative that serves an equivalent purpose, with exceptions for purely decorative images. It also gives search engines and other systems additional context about the content of a webpage. Not every image needs a detailed description, but understanding when and how to use alt text is just as important as knowing what it is.

Examples of Bad, Good, and Best Alt Text

Consider an image of a golden retriever running through a grassy field. A bad description might simply say “dog,” which provides very little context. A better description would be “golden retriever running through a field,” which communicates the main subject and action. An even stronger description might be “golden retriever running through a grassy field with a tennis ball in its mouth,” assuming those details are visible, and more importantly, relevant. Remember, the best alt text isn’t necessarily the longest or most descriptive; it’s the description that communicates the image’s purpose most effectively.

Why Does It Matter?

Alt text serves several purposes across accessibility, usability, and SEO visibility. For users who are blind or have low vision, screen readers can read alt text aloud to convey the meaning or purpose of an image. Alt text may appear in place of an image if it fails to load. It preserves important context that would otherwise be lost.

Google uses alt text and surrounding page content to better understand the subject of an image. This can help images become more discoverable and give search engines additional context about the content of a page.

There is also a standards and compliance component to image accessibility. WCAG is widely used as a benchmark for web accessibility, making well-written alt text an important part of building accessible content.

When Does an Image Need Alt Text?

Rather than simply asking, “Does this image need alt text?” consider: what is the importance of this image, what does it tell users, and would anything be lost if it disappeared?

If an image communicates information, supports the surrounding content, or performs a function, it generally needs a text alternative. If an image displays text, the alt text could repeat what it says verbatim or communicate its general meaning, depending on the image’s purpose. Whenever possible, important text should be presented as actual HTML text rather than embedded within an image.

Decorative images, on the other hand, do not need descriptive alt text. For example, a background shape, divider, or texture (or anything added purely for visual interest) may not provide any meaningful information. In those cases, the image should typically use an empty alt attribute, alt=”“, so that screen readers can ignore it rather than announcing unnecessary content.

How to Write Good Alt Text

When writing effective alt text, the goal should be to keep it concise, clear, and written with the purpose of the image in mind. The same image may even require different alt text, depending on how it is being used elsewhere on the page.

Keep descriptions brief, when possible, while still providing enough contextual information to communicate the image’s purpose. Alt text should also make sense within the context of the surrounding page.

Most importantly, write alt text for people first. There is a time and place for SEO keywords, and that is when they naturally occur while describing the image.

Common Alt Text Mistakes

If alt text is too vague, repetitive, or written without considering the image’s purpose, it can be ineffective.

One common mistake is beginning every description with phrases like “image of” or “picture of.” That practice is redundant since screen readers already identify images as images. Alt text should instead get directly to the information that truly matters.

Another mistake is being too vague, or, conversely, too detailed. One- or two-word descriptions may not provide enough context, while overly long descriptions can create a difficult experience for users who rely on screen readers. Focus on the information the user actually needs, and avoid describing the image with every visible detail.

Charts, graphs, diagrams, and other complex visuals may require additional explanation elsewhere on the page, rather than trying to fit every metric into the alt text.

Avoid keyword stuffing or adding unnecessary search terms solely for SEO. If a keyword naturally describes the image, it can be included, but it should not make the description sound forced or less useful.

WCAG and Alt Text

Alt text is directly addressed within the Web Content Accessibility Guidelines (WCAG), specifically under Success Criterion 1.1.1: Non-text Content. In simpler language, meaningful visual content should have atext alternative so that the information or function it provides is accessible to users who cannot see it.

That does not mean every image needs a written description. Decorative images should typically use an empty alt attribute. This tells screen readers to skip over them. Informative images should communicate their essential meaning, while functional images (like image-based links or buttons) should describe the action they perform.

Ultimately, WCAG reinforces a point that applies throughout this article: the correct approach depends on the purpose and context of the image.

Conclusion

Alt text is a small and often overlooked part of a webpage, but it can have a significant impact on how that page is experienced and understood. Effective alt text promotes accessibility, provides useful context, and can help search engines better understand visual content.

The key is to approach each image intentionally. Consider why the image is there, what information it provides, and whether anything meaningful would be lost without it. Not every image needs a detailed description, but every image should be considered with accessibility and purpose in mind.