What alt text is
Alt text, short for alternative text, is a written description attached to an image. It is read aloud by screen readers, shown when an image fails to load or is blocked, and available to software that cannot interpret pictures. Its job is to give people who cannot see the image the same useful information as people who can.
It is not a caption, a title or a place for keywords. It is a short substitute for the image in its context.
The central question: what is this image doing here?
There is no single correct description for an image. The right alt text depends on the job the image does on that page. The same photo of a bakery counter might need:
- “Fresh sourdough loaves on the counter of our Main Street bakery” on a page about the shop,
- “Cinnamon buns, about to be glazed” in an article about a recipe,
- an empty description if it is only decoration and the text already says everything.
Ask: if this image were removed, what would the reader lose? Write that.
What to describe
- The information the image carries. What is shown that matters for the message?
- The function, when the image is a link or button. Describe the destination or action, such as “Download the brochure”, not the picture.
- Text inside the image. If the image includes words, include them, especially on banners or posters. Better still, put the key text in the page itself.
- The point of a chart or graph. Summarise the main trend or finding in a sentence, and provide the underlying data in a table or nearby text if it is detailed.
- Relevant details of a product. For a jacket, perhaps colour, style and the feature the page is about. Product descriptions in text carry the rest.
- Important people and actions, where relevant. “A customer scans a QR code at the till” is more useful than “people in a shop”.
What to leave out
- “Image of” or “picture of”. Screen readers already announce that it is an image.
- Repetition of nearby text. If the caption or paragraph already says the same thing, a long description doubles the noise.
- Keyword stuffing. Do not pack in search terms. It makes the experience worse for screen reader users and offers no reliable benefit. A natural description is best.
- Unnecessary detail. You do not need to list every colour and object. Include what supports the content.
- Opinions and hype. Avoid “stunning” or “amazing” in descriptions. Describe, do not sell.
- Anything inaccurate or misleading. The description must match the image.
How long should it be?
Usually short: a phrase or a sentence, often around 125 characters or fewer, though this is a rule of thumb rather than a hard limit. Some screen readers may not handle very long text well. If a complex image needs a longer explanation, such as an infographic, give a brief alt text and put the full explanation in the page text or in a linked description.
Types of image in marketing
Product photos
Describe what the product is and the features that matter: “Blue canvas backpack with two front pockets and a brown leather strap”. If you have several angles, differentiate them: “Backpack from the side, showing the padded shoulder strap”. Avoid copying the whole product description into each image.
Logos
If the logo is a link to your home page, the alt text should reflect that, like “Company name, home”. If the logo sits next to the company name written in text, empty alt text may avoid repeating it. Otherwise use the company name.
Banners and promotional graphics
If the banner contains text such as “Autumn sale, 20 percent off boots”, the alt text should include that text. If you can, avoid putting offers only in images, as images may be blocked or unreadable.
Charts and infographics
Summarise the key takeaway: “Bar chart: online orders rose each quarter of the year, with the largest rise in the final quarter” (an illustrative example). Offer the numbers in text or a table.
Screenshots
Say what the screenshot shows and what the reader should notice: “Dashboard screenshot with the email sign-up count highlighted”. Do not describe every button.
People photos and stock images
Describe only what is relevant. If the picture is purely mood-setting, it may count as decorative. Be careful with descriptions of people; stick to observable facts and avoid guessing characteristics such as age or ethnicity unless the context makes that information relevant.
Decorative images
Dividers, background flourishes and images that add nothing informational should have empty alt text (alt=""), so screen readers skip them. This is different from leaving the attribute out entirely: if it is missing, some screen readers read out the file name, which can be unhelpful. Leaving it empty is a deliberate signal.
Images of text
Avoid them where possible. Real text can be resized, restyled and read aloud. If you must use one, the alt text should contain the same words.
Where alt text is added
- Your website or CMS. Most systems have an alt text field when you upload or insert an image.
- Email. Add alt text in your email tool for each image, and check how it looks when images are off.
- Social posts. Many platforms offer an image description field, though the name and location vary. Check each platform’s current documentation.
- Documents and slides. PDFs, presentations and documents can carry alt text too, and the tool you use will have an option.
A simple test
- Cover the image and read only the alt text in context. Does the page still make sense?
- Would the description still be useful if the reader never saw the picture?
- Is it short, accurate and free of “image of”?
- Does it add to the surrounding text rather than copying it?
- If the image is a link or button, does the alt text say what happens?
- If it is decorative, is it empty?
Reading your page aloud, or running it through a screen reader, quickly exposes weak descriptions.
Using automatic descriptions
Some tools can generate descriptions automatically. They can be a rough starting point, but they often miss the context and purpose of your image and may get details wrong. Always review and edit them, and never publish a machine guess without reading it.
Build it into your process
Alt text is easiest when it is written at the time the image is chosen, by someone who knows why it is there. Add a field for it in your design briefs and content calendar, and include it in your publishing checklist. It takes a minute per image and makes your pages, emails and posts more useful to more people. As with other accessibility measures, it is worth doing because it serves readers, not because it promises a particular outcome.