Alt text for SEO: what Google actually says

Search “alt text SEO” and you’ll find plenty of confident advice: put your keyword first, stay under 125 characters, add alt text to rank higher. Some of it is sensible, and some of it isn’t backed by anything Google has published. This guide sticks to Google’s own documentation, mainly Google image SEO best practices on Search Central, and marks clearly where we’re giving opinion.

What Google says, quoted

1. Alt text is the most important image attribute.

“The most important attribute when it comes to providing more metadata for an image is the alt text (text that describes an image), which also improves accessibility for people who can’t see images on web pages, including users who use screen readers or have low-bandwidth connections.”

Note how Google frames it: metadata for search and accessibility, in the same sentence.

2. Alt text works together with computer vision and page content.

“Google uses alt text along with computer vision algorithms and the contents of the page to understand the subject matter of the image.”

So alt text isn’t the only signal, but it’s a direct one.

3. Alt text on linked images acts like anchor text.

“Also, alt text in images is useful as anchor text if you decide to use an image as a link.”

That’s one more reason to write link-purpose alt text for linked images (see our guide).

4. Write useful, contextual text, and don’t stuff keywords.

“When writing alt text, focus on creating useful, information-rich content that uses keywords appropriately and is in context of the content of the page. Avoid filling alt attributes with keywords (also known as keyword stuffing) as it results in a negative user experience and may cause your site to be seen as spam.”

5. Context around the image matters.

“Google extracts information about the subject matter of the image from the content of the page, including captions and image titles. Wherever possible, make sure images are placed near relevant text and on pages that are relevant to the image subject matter.”

6. Filenames give “very light clues”.

“The filename can give Google very light clues about the subject matter of the image… my-new-black-kitten.jpg is better than IMG00023.JPG.”

7. Use real <img> elements; CSS background images aren’t indexed.

“Google can find images in src attribute of <img> element… Google doesn’t index CSS images.”

That’s useful for decorative images (CSS backgrounds are a good place for them) and a warning for important images (a hero product shot set as a CSS background is invisible to Google Images).

8. Supported formats for images in src: “BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF”. Always include a fallback src with responsive images, because “some browsers and crawlers do not understand” srcset and <picture>.

What Google doesn’t say

• There’s no character limit in Google’s documentation. The “125 characters” rule comes from accessibility folklore, not from Google. It’s still a reasonable target for most alt text (Shopify recommends 125 or fewer (Shopify Help)), but it isn’t an SEO rule.
• Nothing says the keyword must come first. Write naturally. If the image shows the thing people search for, the words will be there.
• Nothing says alt text is a strong ranking factor for the page in web search. Google’s documentation is about understanding images and appearing in Google Images and image features. Claims like “alt text boosts your rankings by X%” deserve scepticism unless they come with a source and a method.
• No statement that every image needs alt text for SEO. Decorative images with alt="" are fine. Leave them alone.

How this lines up with accessibility

Google’s advice and the accessibility guidance point the same way:

So the safe rule is: write for the person who can’t see the image, and you’ve written for Google too.

Good vs over-optimised: examples

Product page, merino jumper - Over-optimised: alt="merino wool jumper mens merino sweater best merino jumper uk buy merino" - Good: alt="Men's merino wool crew-neck jumper in charcoal, front view"

Recipe blog, finished dish - Over-optimised: alt="easy vegan lasagne recipe best vegan lasagne quick vegan dinner" - Good: alt="Slice of vegan lasagne on a plate, showing layers of spinach, tomato sauce and cashew béchamel"

Local business, storefront photo - Over-optimised: alt="plumber london plumbing services emergency plumber london" - Good: alt="Our van parked outside the workshop on Mare Street, Hackney"

The good versions still contain the words a searcher would use. They just read like descriptions, because they are.

Image SEO checklist (from Google’s guide, plus accessibility)

• [ ] Important images use <img> with a src, not CSS backgrounds.
• [ ] Each informative image has alt text that describes it in context.
• [ ] Linked images have alt text that describes the destination.
• [ ] Decorative images have alt="" (or are CSS backgrounds).
• [ ] Filenames are short and descriptive (linen-shirt-sand-front.jpg).
• [ ] Images sit near relevant text, with captions where they help.
• [ ] Responsive images keep a fallback src.
• [ ] Consider an image sitemap for images Google might not find otherwise (Google’s guide covers this).
• [ ] No keyword lists in alt attributes.

Opinion: where the real SEO win is

Our view, labelled as opinion: for most sites the SEO value of alt text comes from coverage and accuracy, not clever wording. Product images with no alt, or with IMG_4471.jpg, give search engines nothing to go on. Fixing hundreds of those does more than polishing a dozen. It also happens to be what screen reader users need.

That’s how Altpass is built. The checker finds the gaps across your site, the drafts use the surrounding page (title, nearest heading, link destination) so they read as descriptions in context, and nothing gets keyword-stuffed. You approve each one before it goes anywhere.

See where you stand

Run the free Altpass checker on a page that matters for search, such as a top product, category or article. You’ll get a score and a list of images with missing, file-name or generic alt text, ready to fix.

Updated 2026-10-07