Alt Text
Alt text describes an image for people who cannot see it and for machines that cannot interpret it. Learn how to write it and when to leave it empty.
TL;DR
Alt text is a written description of an image, supplied in the alt attribute of an image tag. Screen readers announce it to people who cannot see the image, browsers display it when the file fails to load, and engines read it as a description of the visual content. It is an accessibility requirement first; the search benefits are secondary.
Why alt text matters
An image carries meaning that nothing else on the page expresses, and without alt text that meaning is unavailable to a substantial part of your audience.
- Accessibility: Screen reader users depend on it entirely, and in many jurisdictions it is a legal requirement.
- Machine comprehension: Engines interpret images imperfectly, so a written description is the reliable signal about content.
- Image search: Descriptions are a primary input into whether an image surfaces for a query.
- Graceful failure: When an image does not load, the description still conveys the point.
How to write alt text
Describe what the image shows
State the content plainly, as you would to someone who cannot see it.
Match the context
The same photograph needs different descriptions depending on why it appears. Describe what matters here.
Keep it concise
A sentence is usually enough. Screen readers read the whole string, so long descriptions become tedious to listen to.
Skip the preamble
Nothing needs to start with image of or picture of. The technology already announces that it is an image.
Leave decorative images empty
An empty alt attribute tells screen readers to skip purely decorative graphics, which is correct and better than describing them.
Transcribe text in images
If a graphic contains words that matter, put them in the alt text, since no machine reliably extracts them otherwise.
Alt text vs. image captions
Alt text: In the alt attribute, invisible on the page, read by screen readers and parsers. Describes the image for those who cannot see it.
Image caption: Visible text below the image, read by everyone. Adds context, credit or commentary.
They are not substitutes. A caption saying who took a photograph does not describe what the photograph shows, and alt text repeating a visible caption gives screen reader users the same sentence twice.
Descriptive images are part of a broader question about whether your pages are readable to machines at all. Findrix runs a 31-point technical audit covering page structure, rendering and crawler access. Every gap comes with the fix already written: technical, content and off-site. The audit is free, takes about a minute, and requires no signup.
Alt text by image type
- Product photography: Name the product and the distinguishing detail the image shows.
- Charts and graphs: State the finding rather than the chart type. The takeaway is what matters.
- Screenshots: Describe what the interface is showing and which part is relevant.
- Decorative graphics: An empty alt attribute, so screen readers skip them.
- Logos: The organisation name, plus the word logo only if that distinction matters.
- Images containing text: The text itself, since it is otherwise inaccessible.
The keyword-stuffing habit that made alt text worse
Alt text was treated as a ranking opportunity for years, which produced a generation of descriptions written for crawlers: strings of keywords, product names repeated, category terms appended to every file.
The cost landed on screen reader users, who had to listen to keyword lists instead of hearing what the image showed. The benefit was minimal even at the time and is negligible now.
Writing genuinely descriptive alt text usually includes the relevant terms anyway, because describing a product accurately involves naming it.
Frequently asked questions
Do all images need alt text?
All images need an alt attribute. Content-carrying images need a description; purely decorative ones should have an empty attribute so screen readers skip them. Omitting the attribute entirely is the only wrong answer.
How long should alt text be?
Usually one sentence. Screen readers announce the full string, so long descriptions become a burden. Complex images like detailed charts may warrant a longer description elsewhere on the page.
Does alt text help with AI search?
It gives engines a reliable description of visual content they cannot otherwise interpret well, which helps them understand the page as a whole. Its main value remains accessibility.