Alt text is the words attached to an image for someone who cannot see it. A screen reader speaks those words. A crawler that does not interpret the picture uses them too. The job of the field is simple: say what the picture shows.
Write the picture, not a slogan
A red mug on a table is 'A red mug on a white table.' A photo of your shop front is the shop front, with the street if that matters. A diagram of three steps should name the three steps. If you would not say the sentence out loud, it is the wrong alt text.
Do not paste the same alt text on every image. 'Logo' on the logo is fine once. 'Best plumber in the city' on a photo of a van is not a description of the van. Keyword lists in the alt field do not make the page rank, and they make the page worse for the people who rely on the text.
Which images need it
- Photos and diagrams that carry meaning. Describe them.
- Icons that are the only label on a button. The alt text is the label.
- Decorative lines, spacers, and background shapes. An empty alt tells a screen reader to skip them.
- Images of text. Prefer real text. If the words exist only in the image, the alt text has to carry them.
A missing alt on a content image is a warning. A template that omits alt text will raise that warning on every page built from the template. Fix the template, then check one page of each type. You do not edit fifty pages by hand if they all share one component.
Empty alt is a choice for decoration. A missing alt attribute is an oversight. They are not the same.
A practical way to write the sentence is to cover the picture and say what you remember. If you remember 'the red mug' you have the alt text. If you only remember the slogan you wanted to rank for, you were not describing the picture. Keep it under a sentence or two. Alt text is not a caption essay, and it is not a second title tag. Buttons that are only an icon need the action in the alt text, such as 'Search' or 'Close', because that text is the accessible name of the control.
Where it sits in the score
Image alt text is an on-page check. On-page is 25 percent of the letter. It is one check among titles, descriptions, headings, and canonicals. Clearing every alt warning is worth doing. It is not the whole grade. The published weights are on the methodology page.
The free scan reports images on the homepage that have no alt text. If the homepage is clean and inner pages are not, the template for those pages is the place to look. How to read the report shows which rows to open first.
