Alt text does two jobs at once. It tells assistive technologies what an image means and it gives search engines context about that image. Google explicitly advises writing helpful, information-rich descriptions and warns against packing the alt attribute with keywords. Stuffing looks spammy and can harm users and rankings alike.
What alt text actually is
The alt attribute is a short text replacement for an image. Screen readers speak it out, and browsers show it if an image fails to load. MDN notes the attribute is mandatory in practice and that an empty value signals a decorative image. WebAIM adds that alt text is a textual substitute that helps both people and search engines understand the content and function of images. Context matters more than pure description.
Accessibility comes first
WCAG 2.2 requires a text alternative for non-text content so information can be delivered in different ways, such as speech or braille. That is the baseline standard many audits test against.
Not every image needs words though. The W3C’s guidance is clear: mark purely decorative images with alt="" so screen readers skip them, rather than reading out filenames.
When deciding what to write, use the WAI alt-text decision tree: describe the action for functional images like buttons, include the visible text for images of text if it is not elsewhere, keep simple informative images brief, and provide a separate long description for complex charts.
How alt text supports SEO without the spam
Google uses alt text alongside page content and computer vision to understand what an image is about. It also treats alt text like anchor text when an image is a link. Descriptions should be helpful and in context, and keyword stuffing should be avoided. File names, captions, and nearby copy all contribute small signals too.
The SEO Starter Guide reinforces this: add high-quality images near relevant text and write descriptive alt text that explains the relationship between the image and the page content.
Writing better alt text
Aim for clear, specific, and concise. NN/g recommends keeping it short, roughly up to 150 characters, avoiding filler like “image of”, and tailoring the description to the image’s purpose on the page. That keeps things usable for people listening on screen readers.
A few practical tips drawn from accessibility rules and real-world testing:
- Describe meaning, not pixels. Say what the image conveys in this spot.
- For linked images, write the destination or action, as you would for link text.
- Brand logos usually just need the organisation name in the alt text.
- Complex charts need a brief alt plus a nearby table or text that carries the full detail.
- Run an accessibility audit: tools like axe flag missing or misused alt attributes and remind you to keep decorative images empty.
When to leave alt text empty
If removing the image would not remove information, the image is decorative. Use alt="". Do not omit the attribute altogether, since some assistive tech will read filenames if alt is missing.
Pure decoration often belongs in CSS backgrounds, which avoids unnecessary alt text entirely.
Good vs poor examples
| Image type | Poor alt text | Better alt text |
| Product photo: blue running shoes | “blue running shoes buy cheap running shoes running sneakers best price” | “Blue men’s road-running shoes, mesh upper, white sole” |
| Linked logo to home | “company logo” | “Myoho Marketing” |
| CTA button that is an image | “button” | “Start free audit” |
| Decorative wave divider | “wave graphic” | alt="" |
These examples follow WAI’s guidance on functional, informative, and decorative images, plus Google’s advice to avoid keyword stuffing.
Quick checklist you can apply in your CMS
- Does the image communicate something the text does not? If yes, write a short, specific alt. If no, set
alt="". - Is the image a link or button? Describe the action or destination.
- Could a screen reader user understand the page without hearing this alt? If yes, it may be decorative.
- Have you avoided “image of”, jargon, and long lists of keywords? Google calls out keyword stuffing as spam, and screen reader users find it tedious.
- For charts, supply the main message in alt, and provide the full data in nearby text or a table.
Good alt text makes pages more inclusive and easier to understand, and it can lift visibility in image search without gaming the system. Write for people first, keep descriptions tied to page context, and reserve keywords for the spots where they naturally fit. Google will still get the signals it needs, and your visitors will get a cleaner, more usable experience.
Book a Image SEO and accessibility audit with Myoho Marketing
How we help: We find fast fixes across missing or unhelpful alt attributes and heavy images.
You get:
- Review of 50 images with clear keep, rewrite or empty-alt calls
- File naming, captions and placement advice that supports context
- A short action list for developers and content teams
