Alt text: writing image descriptions that earn their place

Alt text is the written description attached to an image, read aloud by a screen reader and shown when the image fails to load. It exists so that someone who cannot see the picture gets what the picture was there to convey. That framing answers most questions about how to write it, including the one people ask first — how long should it be — because the answer is: long enough to carry the same meaning, and not a word more.

Two failure modes dominate. The first is the empty field, which turns an image into nothing for anyone using a screen reader. The second is keyword stuffing left over from an era when it worked — descriptions written for a search engine rather than a person, which are useless as descriptions and no longer help ranking either.

How to write it

1. Ask what the image is doing on the page. A photograph illustrating a product, a chart carrying data and a decorative background stripe need three different answers.
2. Describe the meaning, not the pixels. Team of four on a building site in high-visibility jackets beats photograph of people, and beats construction team teamwork professional builders by a wider margin.
3. Keep it to a sentence. Screen readers announce the whole thing without pausing, and a paragraph is punishing to listen to.
4. Do not start with image of or picture of — the screen reader has already said it is an image.
5. Include text that appears inside the image, because otherwise it is invisible to anyone not seeing it.
6. For a chart, give the finding rather than the shape: Revenue fell in Q3 then recovered, not bar chart of quarterly revenue. Put the underlying numbers nearby if they matter.

Decorative images should have an empty alt attribute — written as alt="" rather than omitted. That is the instruction to skip it, and it is a genuine improvement: a screen reader announcing seven decorative dividers is worse than silence. Leaving the attribute off entirely is different and makes some readers announce the filename, which is how people end up hearing IMG_20240714 read out letter by letter.

The cases that trip people up

• An image that is also a link: describe where the link goes, not what the picture shows. A logo linking home is Home, not Company logo.
• The same image used twice on a page: describe it once meaningfully, and let the second instance be decorative if it adds nothing.
• Product photographs: describe what distinguishes this one — colour, angle, what is included — rather than repeating the product name already in the heading.
• Text rendered as an image: reproduce the text exactly. Better still, do not render text as an image.
• Complex diagrams: a short alt plus a longer description in the page body, since a diagram rarely fits in one sentence.

Alt text and search

It does help image search, and it helps modestly with page context, which is why the keyword-stuffing habit persists. Both benefits arrive from describing the image accurately — the same text that serves a person. Writing for the search engine and writing for the reader converged some years ago; anyone still selling you the distinction is selling an old technique. The wider search picture is in seo checklist.

Doing it at scale

Ettex Sites prompts for alt text where images are added, and the accessibility question this sits inside is covered in wcag. The one practical rule for an existing site is to fix the images that carry meaning first — product photographs, charts, anything that is also a link — and leave decorative ones marked as decorative rather than working alphabetically through a list.

What we do not do: there is no automatic image description, no bulk generation, and no accessibility scanner. Alt text is written by whoever knows why the image is there, which is a person; software that guesses produces plausible descriptions of the wrong thing, and a confident wrong description is worse than a missing one.