What alternative text is
Alternative text, often shortened to alt text, is a short written description attached to an image. Screen readers read it aloud or send it to a braille display, so people who cannot see the image still get its meaning. It is also shown if the image fails to load, and it can help with search and with people who have images switched off to save data.
The key idea is that alt text is not a caption and not a full visual inventory. It should answer a simple question: if this image were not here, what would the reader need to know in its place?
Start with the purpose
The same photo may need different descriptions on different pages. A photo of a bridge on a travel page might call for the appearance of the bridge. On a page about engineering history, the relevant details might be the materials or the shape of the arches. Before writing, ask why you included the image.
Images usually fall into a few categories.
Informative images
These add information the text does not fully cover. Describe the relevant content in a sentence or two. For example, for a photo in a how-to article: “A hand holding a pair of scissors at a slight angle, cutting along a pencil line drawn on blue fabric.”
Functional images
If an image is a button or a link, such as an arrow or an icon, the text should describe the action or destination, not the picture. “Download the schedule” is more helpful than “downward arrow.” This overlaps with how you write link text: the wording should make sense when read on its own.
Decorative images
Images that add only visual flavor, such as a divider line or a background swirl, do not need a description. Use an empty alt attribute so screen readers skip them. Many publishing systems have a “decorative” checkbox for this purpose. Leaving out alt text altogether is different, because some readers then announce the file name, which is noise.
Complex images: charts, diagrams and infographics
A short alt text can name the image and state the main point, such as “Bar chart comparing monthly website visits, showing a rise from January to June.” The detailed data should then appear elsewhere on the page, in a table or in the surrounding text, so readers who cannot see the chart can reach it. This also helps readers who find it easier to work with numbers than with graphics. If you are creating simple diagrams from the start, write the text explanation alongside the visual.
Images of text
Avoid putting important text inside images where possible. If you must, the alt text should repeat that text exactly. Real text is better, because it can be resized, searched and read by software.
A practical method
- Identify the purpose of the image on this page.
- Look at what matters. Which details support that purpose? Ignore the rest.
- Write it as you would say it to a friend on the phone, in plain words.
- Keep it short. One or two sentences is typically enough, and many descriptions work well in a single short phrase. Very long alt text is hard to listen to and cannot be skimmed.
- Check it against the page. Read the surrounding text with your description in place. Does it repeat the caption? If so, trim it.
Common mistakes
- “Image of” or “Picture of.” Screen readers already announce that it is an image. Start with the content. Mention the type only when it matters, as in “Watercolor painting of…” or “Black-and-white photograph of…”.
- File names or keyword stuffing. “IMG_4032.jpg” tells nobody anything, and stuffing search terms into descriptions is both unhelpful and discouraged.
- Repeating the caption word for word. If a caption already describes the image, keep the alt text short or focus on what the caption leaves out.
- Describing everything. A photo of a busy street does not need every car and sign. Choose what supports the point.
- Guessing. Do not claim a person’s emotions, identity, age or background unless you know them and it matters. Describe visible features neutrally, and name people only with their consent and where relevant.
- Leaving it blank on important images. Unlabeled informative images leave readers out.
Special cases
People in photos
Describe what is relevant, such as actions, clothing or setting, only when it matters. If a person is named in the caption, you do not need to repeat it. Be respectful and avoid assumptions about gender, ethnicity or ability unless the person has shared those details and they are important to the content.
Memes, screenshots and social posts
For a screenshot, include the text that matters and describe what the screenshot shows. For a joke image, convey both the picture and the text so readers get the point.
Art and photography
For creative work where the visual impression is the point, describe the subject, style and mood briefly. A longer description on the page, or in a gallery notes section, can offer more detail to those who want it.
AI-generated descriptions
Automated description tools can offer a rough starting point, but they often miss context and purpose and can be wrong. Always review and edit them, and do not publish them without checking.
Checking your work
Read your alt text aloud without looking at the image. Does it make sense? Ask someone else to read it and sketch what they imagine, or have a screen reader user comment. Over time you will build a feel for how much is enough.
Good alt text is a small act of writing, but it decides whether a reader gets the full story. Keep it purposeful, brief and honest.