Alt Text for SEO: How to Write It

Alt text (the alt attribute on an image) is a short written description of what an image shows. It exists so screen readers can describe images to people who cannot see them, and so search engines and AI can understand an image they cannot fully interpret from pixels alone.

Good alt text is genuinely useful for SEO: it helps your images rank in Google Images, supports accessibility, and gives AI search a reliable signal about what your image means. This guide is part of our image SEO hub, and it covers what alt text is, how to write it with real examples, how long it should be, and how to add it in WordPress and Shopify.

What is alt text in SEO?

Alt text in SEO is the descriptive text you add to an image's alt attribute so search engines understand what the image shows and can index it for relevant searches. In HTML it looks like this: <img src="golden-retriever-puppy.webp" alt="Golden retriever puppy sitting in grass">. The text inside alt is what search engines and screen readers read.

It is sometimes called the alt attribute or, loosely, the alt tag. It is not the same as the file name or the caption. Alt text lives in the HTML, is invisible on the page unless the image fails to load, and is the single most important text signal for telling search engines what an image contains.

Alt text vs title text

Alt text and title text are different. Alt text (the alt attribute) describes the image for screen readers and search engines and shows if the image fails to load. Title text (the title attribute) usually appears as a tooltip on hover and carries little to no SEO weight. Focus your effort on alt text; title text is optional. Your image file name is a third, separate signal.

Does alt text help SEO?

Yes, alt text helps SEO. It is the primary way Google understands what an image shows, which lets your images rank in Google Images and reinforces the topic of the page they sit on. It is a genuine, if modest, ranking and discovery signal, and it is also required for accessibility.

How Google reads alt text

Google uses alt text, along with the file name and surrounding page content, to index an image and decide which queries it should appear for. Clear, descriptive alt text increases the odds your image shows up in Google Images and visual search results. Vague or missing alt text means Google has to guess, and often gets it wrong or skips the image.

Accessibility and screen readers (WCAG)

Alt text exists first for accessibility. Screen readers read the alt attribute aloud so people who are blind or have low vision know what an image conveys. The WCAG accessibility guidelines require meaningful images to have a text alternative, so writing good alt text is both an SEO best practice and a legal and ethical baseline.

Alt text in the age of AI search

Here is the angle most guides skip. Multimodal AI models like ChatGPT, Gemini, Claude and Google AI Overviews can now look at an image and describe it directly, so you might assume alt text no longer matters. It still does. AI crawlers reading your raw HTML rely on alt text the same way Google does, and even when a model can see the image, your alt text confirms intent, adds detail the pixels do not show (a brand name, a model number, a date), and disambiguates similar images. Treat alt text as the caption you write for both screen readers and AI. It is a core habit in AI SEO.

How to write SEO-friendly alt text

Write alt text the way you would describe the image to someone over the phone: specific, accurate and brief. Follow these steps:

1. Describe what is actually in the image, including the important details (what, who, color, action).
2. Keep it concise, ideally under about 125 characters, so screen readers do not cut it off.
3. Include a relevant keyword only if it fits naturally and truthfully.
4. Do not start with "image of" or "picture of"; screen readers already announce it as an image.
5. Leave decorative images with an empty alt attribute so they are skipped.

Alt text examples (good vs bad)

How long should alt text be?

Alt text should generally be under about 125 characters. That is roughly where many screen readers truncate, and it forces you to be specific without rambling. There is no hard SEO limit, but if you need more than a sentence, the extra detail usually belongs in the caption or body text, not the alt attribute.

Using keywords without stuffing

Include your target keyword in alt text only when it honestly describes the image. One natural mention is fine and helpful. Cramming in multiple keywords (keyword stuffing) reads badly to screen reader users and can look manipulative to Google. Accuracy beats keyword density every time.

Decorative images and the null alt attribute

Not every image needs a description. Purely decorative images (background flourishes, spacer graphics, dividers) should use a null alt attribute, written as alt="". This tells screen readers to skip the image entirely instead of reading out a distracting filename. Use empty alt for decoration, descriptive alt for anything meaningful.

How to add alt text in WordPress, Shopify and other platforms

Most content platforms have a built-in field for alt text, so you rarely need to touch code. Here is where to find it:

• WordPress: open the Media Library or click an image in the block editor, then fill in the "Alternative Text" field. Plugins like Yoast SEO can flag images missing alt text.
• Shopify: in the product or media editor, click an image, choose "Edit alt text" (or "Add alt text"), and type your description.
• WooCommerce: uses the WordPress Media Library, so set alt text there for product images.
• Other CMS: look for an "alt text" or "image description" field in the media settings; if you hand-code, add the alt attribute inside the <img> tag.
• Instagram and social: platforms like Instagram have their own alt text field under advanced settings; it aids accessibility but does not affect your website's SEO.

Alt text mistakes to avoid

• Leaving alt text blank on meaningful images (Google and screen readers get nothing).
• Stuffing keywords or repeating the same phrase across every image.
• Starting with "image of" or "photo of".
• Using the file name as the alt text (alt="IMG_4821.jpg").
• Writing the same generic alt text on every product variant instead of describing the differences.
• Forgetting alt="" on decorative images, which makes screen readers read clutter.

Alt text is one of several image signals. Pair it with a clean file name, the right format, and proper compression for the full effect.

Audit and generate alt text at scale with DataWise

If your site has hundreds of images, checking alt text by hand is painful. DataWise, our SEO tool that is free for AI Ranking members, crawls your site, lists every image missing alt text, and can draft accurate AI alt text suggestions you review and approve. It works like a built-in AI alt text generator with a human in the loop, so you fix the whole site in an afternoon instead of a month.

Inside the community we run alt text audits together and coach you on writing descriptions that serve accessibility, image rankings and AI search at the same time.