Alt text for Images and How to Write Effective Descriptions

Alt text for images is the written description that explains what an image shows and why it exists on a page. Its primary role is accessibility—helping screen readers describe images to users who cannot see them—but it also plays a supporting role in SEO by helping search engines understand image content in context.

When written properly, alt text improves user experience, supports inclusive design, and reinforces page relevance. When written poorly—or ignored entirely—it creates accessibility gaps and weakens how search engines interpret visual content. This guide explains alt text in a clear, practical way and shows how to write it correctly without overcomplicating the process.

What alt text is and how it works

Alt text (short for “alternative text”) is the text stored in the alt attribute of an image. If an image cannot be displayed or a screen reader is used, this text is read aloud or shown instead of the image.

Alt text exists to replace the meaning of an image, not to describe every visual detail. Its job is to convey what the image contributes to the page.

What alt text should and should not do

Alt text should describe the image’s content or function in context. It should not be used as a caption, a marketing pitch, or a keyword container. For images that do not add meaning—such as decorative shapes or visual dividers—alt text should be empty so assistive technologies skip them.

Why alt text matters for accessibility and seo

Alt text is one of the simplest ways to make a website more accessible and more understandable to search engines. It directly affects how users experience content and how machines interpret it.

Accessibility and user experience

Screen readers rely on alt text to explain images. Without it, users miss important context or hear confusing placeholders. Clear alt text improves comprehension, reduces friction, and supports inclusive access to content.

For complex visuals like diagrams or charts, alt text should summarize the key idea, while longer explanations can live in surrounding text or captions.

How search engines use alt text

Search engines use alt text to understand what an image represents and how it relates to the page topic. This helps with image indexing and reinforces topical relevance for the page as a whole.

Alt text is not a ranking trick. It works best when it is accurate, natural, and aligned with the content—not stuffed with keywords.

Writing good alt text the right way

Good alt text is simple, specific, and contextual. It describes what matters about the image, based on why the image exists on the page.

How to write effective alt text

Start by asking why the image is there. Is it explaining something, showing a product, supporting a point, or triggering an action? The answer determines what the alt text should say.

Describe the subject and action clearly, using natural language. Keep it concise. Most useful alt text fits comfortably within one sentence.

Avoid phrases like “image of” or “picture of.” Screen readers already identify the element as an image.

Examples of strong and weak alt text

Strong alt text describes the meaning:

• “Black running shoes with breathable mesh and cushioned sole”

• “Diagram showing how solar panels connect to an inverter”

Weak alt text adds little value:

• “Image”

• “Product photo”

• “Shoes”

For decorative images, use an empty alt attribute so they are ignored by screen readers.

Handling complex images and special cases

Not all images can be explained in a single short sentence. Some visuals require layered descriptions.

Diagrams, charts, and infographics

Alt text should explain the main takeaway, not every data point. If the image contains detailed information, include a longer explanation in nearby text or a caption.

Logos and branding

Logos should include the brand name and context, such as “CompanyName logo in website header.” This helps users understand identity and navigation.

Image buttons and icons

If an image acts, the alt text should describe that action, not the appearance. For example, “Search” or “Submit form.”

Implementing alt text across platforms

Alt text should be added wherever images are uploaded, regardless of platform. The process is simple but must be consistent.

HTML and code-based sites

Use the alt attribute directly in the image tag. Decorative images should use an empty alt value.

Content management systems

Most CMS platforms include an “Alt text” or “Alternative text” field when uploading images. This field should always be filled for meaningful images.

For large sites, consistency matters more than perfection. Start with critical pages and expand coverage over time.

Auditing and maintaining alt text at scale

Alt text is not a one-time task. As content grows, it needs review and maintenance.

How to audit alt text effectively

Run periodic crawls to identify images missing alt text or using generic descriptions. Prioritize pages that drive traffic or conversions.

Review for clarity, relevance, and repetition. Multiple images on the same page should not reuse identical alt text unless they show the same thing.

Building a sustainable workflow

Create a simple internal guideline defining how alt text should be written for products, diagrams, logos, and decorative images. Enforce alt text entry during publishing and review it during content updates.

Advanced considerations for image seo

Alt text works best when combined with other image best practices.

Image sitemaps and discovery

Image sitemaps help search engines find images more efficiently, especially on large or media-heavy sites. Alt text strengthens the signals provided by those images.

Multilingual and responsive sites

Alt text should match the page language and remain meaningful across devices and image sizes. Translated pages require translated alt text, not reused English descriptions.

Conclusion

Alt text is a small detail with a large impact. It improves accessibility, clarifies content meaning, and helps search engines understand visual elements within a page. When written thoughtfully, it supports both users and SEO without adding complexity.

The goal is not to optimize alt text for algorithms, but to describe images clearly and honestly in context. By doing this consistently—across platforms, content types, and workflows—you turn images into fully integrated, accessible, and searchable content assets.