When is alt text necessary vs noise for a screen reader?

Alt text is necessary when an image carries information or performs a function, and it is noise when the image is purely decorative. The test is whether the image adds meaning a screen reader user would otherwise miss: if it does, describe it; if it does not, mark it so the screen reader skips it entirely. The crucial detail is that skipping is itself a deliberate act, accomplished with an empty alt attribute (alt=””), which tells assistive technology this image is decorative and should be passed over silently rather than announced.

The reasoning is that a screen reader reads alt text aloud, so every alt value is something a user has to listen to. Description is valuable when it replaces information the image conveyed, and it is friction when it narrates pixels that carry nothing. The default instinct to “add alt to everything to be thorough” backfires, because it forces users to sit through announcements of borders, spacers, background flourishes, and stock photos that add no meaning. Thoroughness here is not maximal description; it is accurate triage, saying what matters and saying nothing where nothing matters. Length follows the same logic: even an informative image should get the shortest alt that conveys its point, because every extra word is extra listening.

Two concrete cases make the line clear. A product photo on a shopping page is informative: its alt should convey what the item is, “navy wool overcoat, front view,” because that is information a sighted user gets and a screen reader user needs. The thin gray divider line between sections, or the abstract swoosh behind the hero headline, is decorative: it gets alt=”” so the screen reader moves straight to the next real element. A logo that links home is functional, so its alt names the destination, “Acme home,” rather than describing the mark. A fourth pattern is worth its own answer: an image that sits next to text already saying the same thing, like a small calendar icon beside the word “Schedule,” is redundant rather than informative, so it gets alt=”” to avoid the screen reader announcing “Schedule” twice. Same logic, several correct answers, none of them “describe it because it is there.”

What sits outside this is that this rule decides whether alt is needed, not how to write a good description. Judging informative versus decorative is the upstream question; crafting concise, useful wording for the informative ones is a separate craft. There are also edge cases where the same image is decorative in one context and informative in another, so the test is contextual, not a property of the file: a photo of a watch is decorative as a lifestyle banner and informative as the product being sold. And a missing alt attribute is not the same as an empty one, which is the most common mistake in this whole area: omitting alt entirely can make a screen reader fall back to reading the filename aloud, while alt=”” intentionally silences the image. The choice is always describe or deliberately skip, never leave undecided.

Go through every image and sort it before writing a word: does this carry information or function, or is it decoration. Give the informative and functional ones alt that conveys their meaning or destination, and give the decorative and redundant ones an explicit empty alt so they are skipped. Resist adding alt to everything, never leave the attribute off entirely, and treat each empty alt as a chosen “skip this,” so the screen reader hears what matters and stays silent on what does not.