How To Write Alt Text
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Who actually reads alt text
Alt text is the short written description of an image that screen readers announce to blind and low-vision users, that browsers display when an image fails to load, and that search engines use to understand your visual content. Good alt text is specific, short, and written for the context the image lives in; bad alt text is either missing, stuffed with keywords, or bizarrely literal. Getting this right is the single biggest accessibility improvement most websites can make, and it compounds because every image on every page benefits. This guide covers the purpose of alt, when to describe versus caption, the special case of decorative images, length guidance, and how alt text interacts with SEO.
Describe, don’t caption
Four real audiences consume alt text, not one:
Length: short but not too short
Good alt text serves all four at once. You’re not writing for a machine or for a specific user group; you’re writing for whoever can’t see the pixels.
Decorative images: empty alt
A caption is editorial commentary shown to sighted readers: “Our founder Jay at the 2026 launch event.” Alt text is a functional description: “A man in a blue blazer holding a microphone on a small stage with a purple banner behind him.”
Context matters more than the picture
The test: if the image disappeared, would the alt text convey what the image added to the page? If yes, it’s good alt. If the alt just says “Jay at launch” and you’d lose the informational value, it’s captioning, not describing.
Functional images: describe the action
When the image truly is just illustrating the caption, you can repeat the caption as alt — but usually a fuller description is better.
Complex images: charts, diagrams, infographics
Not every image carries information. Decorative images — background textures, purely aesthetic flourishes, an emoji-like icon beside a label that already names the concept — should have an explicitly empty alt attribute:
Alt text and SEO
The same image can deserve different alt text depending on where it appears. A photo of a red dress on a product page needs alt describing the product: “Red A-line cotton dress with cap sleeves and a V-neckline.” The same photo in a blog post about color theory might need: “A saturated red dress against a pale gray wall.”
Don’t start with “image of”
Describing pixels here is a classic mistake that leaves screen-reader users lost.
People in images
A data chart can’t be summarized in 120 characters. The good-practice pattern:
Testing your alt
Google has said publicly that alt text helps search engines “understand the subject matter of the image.” Good descriptive alt — the same kind that’s good for accessibility — is good for image search and for the broader ranking of the page.
Writing alt for a screenshot
Keyword-stuffed alt (“cheap red dress buy red dress online red dress sale”) is obvious and penalized. Write for a human first and you’ll get the SEO value as a byproduct.
Alt versus title versus caption
Screen readers already announce “image” before reading alt text. Starting alt with “image of” or “picture of” creates “image image of a dog” — redundant and amateur. Just describe the content.
Animated GIFs and video posters
Describe what’s relevant for the context. Name known people (“Jay Smith, founder”) when context expects it. For stock photo subjects or unnamed people, describe race, gender, and age only when relevant to the point — a feature about diversity in hiring benefits from it; a generic blog header does not.
Localization of alt text
When in doubt, err toward describing what’s visible without speculation. “A smiling woman in a lab coat” beats “a happy scientist.”