Alt text SEO: what Google says actually helps

Alt text is often treated as a place to put keywords. Google's own image documentation points the other way. It calls alt text the most important attribute for giving an image metadata, and it asks for useful descriptions written in the context of the page. This guide goes through what that documentation says, what it leaves out, and how to write alt text that serves a screen reader user and a search engine at once. It makes no ranking promises, because its sources make none.

Missing alt text is common, so the basics are not wasted effort. The WebAIM Million 2026 analysis found that 16.2% of all home page images, 10.8 per page on average, had missing alternative text (not counting alt=""). Our sources are Google's image SEO best practices (the page shows an update date of March 2, 2026), Google's spam policies, the W3C and WebAIM. For how to write alt text in the first place, start with our complete guide to alt text and the alt text examples.

What Google's image documentation says

Google's page covers more than alt text. These are the parts that matter for writing it, with our reading of what each means in practice.

What the documentation does not say

• It gives no weight for alt text compared with other signals, no length limit, and no figure for traffic or ranking.
• It does not tell you to put a keyword in every alt text.
• It does not discuss decorative images or empty alt at all. Nothing on the page supports a claim that alt="" on decoration costs you anything.

WebAIM's alt text article, last updated in October 2021, says in the same direction that search engines use alternative text and factor it into their assessment of the page's purpose and content. It gives no numbers either. A claim of a specific ranking gain from alt text goes beyond these sources.

Common advice, checked against the sources

Keyword stuffing: what it is and why it fails twice

Google's spam policies define keyword stuffing as filling a page with keywords or numbers to manipulate rankings, often in lists or groups, unnaturally or out of context. The image documentation applies the same idea to alt text. Its example ladder runs from a missing alt, to an attribute packed with puppy and dog terms and "cheap dogfood," to a bare "puppy," to the best version, "Dalmatian puppy playing fetch."

It fails twice. Search is one failure: Google says stuffing results in a negative user experience and may get a site treated as spam. The listener is the other. Every extra term is something a screen reader user may have to sit through before the next thing on the page. WebAIM calls injecting "information directed to search engines" into alt text a mistake "too commonly seen across the web." Here is the same idea on an invented product page. The photo shows a matte black gooseneck kettle with a wooden handle on a kitchen counter, and the target keyword is "gooseneck kettle."

A quick test: read the alt text aloud. If a word is there only because you want to rank for it, take it out of the alt text and put it somewhere that is true, such as the caption, a heading or the sentence beside the image.

File names, captions and the text around the image

File names. Google calls the file name a very light clue and recommends short, descriptive names, so matte-black-gooseneck-kettle.jpg is better than IMG_4471.jpg. A descriptive file name is not alt text and cannot replace it. The reverse mistake happens too: a CMS fills the alt field from the file name, and nobody replaces it. Our free scan flags alt text that is a filename or a placeholder such as "image".

Captions. A caption is visible to every visitor and, Google says, a source of information about the image's subject. Use the caption for what the page wants to say about the picture and the alt text for what the picture shows. WebAIM advises that the alt text and the figcaption should not repeat each other.

The text around the image. Google advises placing images near relevant text, on pages that match the image's subject. That also helps people. For product pages, see our guide to alt text for product images, and for where to edit alt text on your platform, Shopify and WordPress.

Real image elements. Google's page contrasts an img element with a div that has a CSS background and states that CSS images are not indexed. So an image that carries content belongs in an img element with alt text. For an inline SVG, Google's example gives the svg an aria-labelledby that points to its title element; our chart alt text guide shows an SVG pattern in full.

The path where accessibility and SEO agree

Where SEO folklore and accessibility pull apart, the sources split. On stuffing, Google's documentation sides with the listener. On very long alt text, "image of" and decoration, Google says nothing, and the W3C and WebAIM guidance applies. The path that satisfies both is short:

1. Decide what the image is for. Informative, functional, decorative or complex. The W3C decision tree in our examples walks through it.
2. Write for the listener. One sentence on what the image shows in this context, without "image of."
3. Check for a natural keyword. If your target phrase accurately describes the image, such as the product type or subject, it is probably already there. If it does not, leave it out.
4. Put everything else where Google says it looks. The file name, a caption, image titles and the text beside the image.
5. Match the markup to the job. Content images in img elements. Decoration in CSS or with an empty alt, per the decorative image guide. Charts with a long description.
6. Have the result checked against the picture. A person, or a tool that opens the image, compares each alt text with its image.

Where our tools fit

The alt text generator has three styles. Its SEO style tells the model to write alt text that is accurate for screen reader users and useful for image SEO, to work in one of your target keywords only if it genuinely matches the image, and never to stuff keywords that do not fit. The Descriptive style is the default and the one we suggest for most images. The generator cannot see your page, so use the context field, and read every draft against the image. We have not measured how accurate generated alt text is; our accuracy test covers judging existing alt text, not writing it.

The alt text checker is not an SEO tool. It downloads up to six images from a page and asks whether each alt text is true of its image. It does not measure keyword density, rankings or search visibility. What it does help with is the part Google and the W3C agree on: alt text that matches what the picture shows. See what we check for exactly what the scan and the audit cover.

Alt text is an accessibility requirement before it is a search tactic. It is the subject of WCAG 1.1.1, and it is one part of making a website accessible.