Start with the image’s purpose
Alt text is a short text alternative for an image. It can help someone using a screen reader understand information they cannot see, and it may appear if the image fails to load. To write it well, start with the page rather than the image alone: why is this image here, and what would a reader miss without it?
An informative image contributes something to the content. A photo might show the difference between two products; a screenshot might identify a setting; a diagram might explain a process. Describe the part that matters to the reader’s task. If a page explains how to find a setting in a menu, “Accessibility settings under the Advanced menu” is more useful than “Screenshot of a computer screen.”
Not every image needs a spoken description. A purely decorative flourish adds no information, while a nearby caption or paragraph may already convey everything an image shows. In those cases, an empty alt value can keep the image from interrupting the reading experience. This is different from accidentally leaving an informative image without a text alternative.
Describe the useful detail, not every visible detail
Write a concise description that lets a reader grasp the image’s point. Include names, labels, relationships, or visible differences when they are important. Skip background details that do not affect the meaning. For a product comparison, “Two backpack straps: the left is padded and the right is unpadded” communicates more than a list of colors and objects in the room.
Context changes the right wording. The same photograph of a bicycle could support an article about brake placement, frame shape, or safe storage. Its alt text should describe the relevant feature for that page, not attempt to catalogue the whole photograph. Avoid opening with “image of” or “picture of” unless the fact that it is a photograph, illustration, or other type of image matters.
Use ordinary language. Alt text is not a place to repeat a target search phrase or add terms that the image does not show. A clear description may naturally include a relevant term, but its first job is to convey meaning to a person. Search-oriented wording that obscures the image’s purpose makes the page less useful.
Handle links and controls by their action
When an image is also a link or button, the text alternative should usually explain what activating it does. For a magnifying-glass button that starts a site search, “Search the site” is more helpful than “Magnifying glass icon.” For a linked image leading to a sizing guide, “View the sizing guide” may be clearer than a visual description of the thumbnail.
Consider the surrounding link text before writing. If an image sits beside a visible label within the same link, repeating that label in the alt text can create an awkward duplicate announcement. The aim is to give the control one clear, understandable name, not to describe each of its parts separately.
Give charts and diagrams enough support
A short alt description can identify a chart’s main takeaway, but it may not carry all the information a reader needs. For a chart comparing three categories, name the categories and the key relationship if it is central to the argument. If exact values matter, provide them in nearby text or a table rather than trying to squeeze every label and number into one alt field.
The same principle applies to diagrams and screenshots. Alt text can orient the reader—“Flowchart showing a request moving from the contact form to the support queue”—while adjacent instructions explain each step. For a complex image, check whether a reader who never sees it can still follow the article. If not, expand the surrounding explanation as well as improving the alt text.
Review alt text in the page, not in a spreadsheet alone
Before publishing, read the paragraph before the image, its alt text, and the paragraph after it in sequence. Does the description add what is missing, or does it merely repeat a caption? Does it assume knowledge the reader has not yet been given? This quick context check often reveals a better description than looking at the image file by itself.
Also check the rendered page. Confirm that informative images have appropriate text alternatives, decorative images are handled deliberately, and linked images have meaningful names. Image filenames and captions can be useful for managing a site, but they do not replace alt text. Treat each field according to its purpose.
The strongest alt text is rarely the longest. It gives readers the information they need at the moment they encounter the image, while the surrounding page carries the fuller explanation. That makes the content easier to use without turning image descriptions into a keyword checklist.
