Image alt text is the value of an image's alt attribute: a short description of what the image shows or does. Screen readers read it aloud, browsers display it if the image fails to load, and search engines use it, together with the surrounding text and file name, to understand the image. Alt text is first an accessibility requirement, and the SEO benefit follows from writing it well.
What it looks like
The alt attribute sits on the img element.
<img
src="/images/approval-flow-dashboard.png"
alt="Quillbrook dashboard showing three pending expense approvals with approve and reject buttons"
/>How to write it
Describe what someone would need to know if they could not see the image, in the context of the page. A product screenshot in a setup guide should describe the screen and the step it shows. A chart should state what the chart shows, ideally its main takeaway.
- Be specific and concise. One clear sentence is usually enough.
- Do not start with “Image of” or “Picture of”; screen readers already announce it as an image.
- Include a relevant keyword only if it describes the image honestly.
- For a linked image, describe where the link goes, since the alt text acts as the link's anchor text.
Decorative images
Images that add nothing to the meaning, such as background flourishes or divider graphics, should have an empty alt attribute (alt="") so screen readers skip them. Leaving the attribute out entirely is different: some screen readers then read the file name, which is worse.
Alt text and image search
Google's image guidance recommends descriptive alt text, descriptive file names, and placing images near relevant text. For most SaaS companies image search is a small traffic source, but product screenshots and diagrams can surface for “how to” and template searches, and alt text is part of how they are understood.
Example
Screenshots in a help article
A made-up HR platform, Peoplepath, publishes a guide to running a performance review cycle with eight screenshots, all with alt="screenshot".
After a rewrite, each screenshot describes the step: “Review cycle settings page with the self-review and manager review toggles turned on”. The guide becomes usable for screen reader users, and each image now reinforces the step it illustrates.
Common mistakes
Stuffing keywords into alt text
Alt text like “best HR software HR platform performance review software” is unhelpful to screen reader users and is treated as keyword stuffing.
Putting important text only in images
Pricing tables, feature lists and headings rendered as images are hard for search engines and assistive technology to read. Put the text in HTML.
Questions
It helps Google understand images and can help pages appear in image search. Its effect on a page's ranking in regular web results is likely small, and it should be written for accessibility first.
There is no strict limit in HTML, but long descriptions are tiring to listen to. Keep it short; if an image needs a long explanation, such as a complex chart, put that explanation in the page text.
