Who alt text is for
A screen reader user, first and mostly. Alt text is read aloud in place of the image, which is why the rules that matter are about speech rather than about keywords: it should be short enough to listen to, specific enough to be worth hearing, and it should not begin by announcing that it is an image, because the screen reader has already said so.
It is also what a browser shows when an image fails, what a search engine reads, and — on a page where images carry real information — the difference between a usable page and a decorative one. But a description written for a search engine and a description written for a listener are not the same text, and when they conflict the listener wins.
The length to aim for is under 125 characters. Some screen readers cut longer text; more importantly, a long alt text is a long interruption. If an image genuinely needs a paragraph, that paragraph belongs on the page as a caption, where everyone can read it.
- Never begin with "image of" or "photo of".
- Describe what the image shows, then what it is there to convey.
- A decorative image takes an empty alt attribute, not a description.
What to write, by what the image is doing
The single most useful question is not "what is in this image" but "what is this image for". Four answers, four different alt texts.
| The image is | Write | Example |
|---|---|---|
| Decorative | Nothing — an empty alt attribute | alt="" |
| Illustrating a point | What it shows, in the terms of the point | "Reminder settings with a 24-hour and a 2-hour reminder enabled" |
| Carrying data | The finding, not the chart type | "No-shows fell from 14% to 6% after reminders were added" |
| A link or a button | Where it goes or what it does | "Start a free trial" |
How to choose and edit
Read each option out loud. Alt text is speech, and a sentence that reads fine on screen often turns out to be a mouthful. The one that is easiest to say is usually the one to keep.
Then check it against the page. Alt text that repeats the caption or the sentence beside it makes a listener hear the same thing twice; alt text that describes something not visible in the image is simply wrong. And if the image is there for atmosphere rather than information, the right answer is an empty alt attribute, which no generator will ever suggest because you did not ask it for nothing.
Keep the keyword out of it unless it belongs. Alt text stuffed with a keyword is an old tactic that now mostly annoys the people it is read to, and search engines have been discounting it for a long time.
Alt text that is written where the image is made
The reason alt text is so often missing or bad is that it is written in the wrong place: after the fact, by someone looking at a filename in a media library, with no idea what the image was meant to convey.
In PrismDraft the image and its alt text are made together. Each section's image is prompted from the paragraphs it sits beside, which is also where the alt text comes from, and it is written in the article's language. It is editable before you approve the article, and it travels with the image when the article publishes — inside the post's HTML on WordPress and Shopify, in the body on Webflow, and on Ghost's feature image.
Questions
How long should alt text be?
Under 125 characters. Some screen readers truncate past that, and a long alt text is a long interruption to someone listening to the page.
Does this read my image?
No. It works from your description, and nothing is uploaded. That is a real limitation: it cannot correct you about what the image shows.
What about decorative images?
Give them an empty alt attribute so a screen reader skips them. Describing a background texture is worse than describing nothing.
Should I put the keyword in?
Only where it genuinely describes the image. Keyword-stuffed alt text annoys the people it is read to and has been discounted by search engines for years.
What about charts and screenshots?
State what they say, not what they are. "Bar chart of monthly figures" is useless to a listener; the finding the chart shows is the alt text.
Is my description stored?
No. The request is read, answered and forgotten.