How to Write Alt Text (for Accessibility & SEO)

To write alt text, describe what the image shows accurately and concisely, in a way that conveys its meaning to someone who can’t see it, including a relevant keyword only where it fits naturally. Alt text exists first for accessibility — it’s what screen readers announce to visually impaired users — and it helps search engines understand images second. Describe the image honestly; never keyword-stuff. Here’s how, with examples.

This guide covers writing effective alt text — accessibility first, SEO second, with the rules that matter.

First: what alt text is really for

Getting the purpose right shapes everything: alt text (the alt attribute on an image) exists primarily so screen readers can describe images to visually impaired users — it’s an accessibility feature. It also helps search engines understand images they can’t “see,” which aids image SEO. So write alt text for a human who can’t see the image first, and the SEO benefit follows naturally. This framing prevents the biggest mistake: keyword-stuffing that helps no one.

Step 1 — Describe the image accurately

Write what the image actually shows, specifically. “Golden retriever puppy sleeping on a blue blanket” is far better than “dog” or “image.” Be accurate and specific enough that someone hearing it understands what’s there. Accuracy is the whole job.

Step 2 — Keep it concise

Alt text should be brief — a phrase or short sentence, not a paragraph. Screen readers read the whole thing aloud, so long alt text is tiresome. Aim to convey the essential content and function of the image in a few words. (Roughly a sentence is a good ceiling for most images.)

Step 3 — Include a keyword only where it fits naturally

If a relevant keyword genuinely describes the image, include it — that helps image SEO. But never force it or stuff keywords. “Red running shoes on a trail” (natural) beats “running shoes buy running shoes best running shoes” (stuffed and useless to a screen-reader user). Describe first; the keyword belongs only if it’s part of an honest description.

Step 4 — Use empty alt for decorative images

This is the nuance SEO lists usually miss: if an image is purely decorative — a background flourish, a divider, an icon that adds no information — give it an empty alt attribute (alt=""). This tells screen readers to skip it, so users aren’t bothered by meaningless descriptions. Not every image needs descriptive alt text; decorative ones should be explicitly marked empty, not described.

Step 5 — Don’t start with “image of” or “picture of”

Screen readers already announce that it’s an image, so starting alt text with “image of…” or “picture of…” is redundant. Jump straight to the description: “Chef plating a dish” not “Image of a chef plating a dish.” (Exception: specify the type if it matters — e.g. “Illustration of…” or “Diagram showing…” when the format is meaningful.)

Step 6 — Convey function for functional images

If an image is also a link or button, the alt text should describe its function/destination, not just its appearance — e.g. a logo linking home might be alt="Launch with Bryan home". For a functional image, what it does matters more than what it looks like.

Examples

• Bad: alt="IMG_2938" or alt="dog dog puppy cute dog buy" (unhelpful / stuffed)
• Decorative: alt="" (correctly skipped)
• Good: alt="Golden retriever puppy sleeping on a blue blanket" (accurate, concise, natural)
• Functional: alt="Download the free SEO checklist" (describes what the button does)

Write alt text as an accurate, concise description for someone who can’t see the image, mark decorative images empty, and let keywords appear only when honest — that’s alt text done right, for people and search alike. (Web design builds accessible, well-optimized sites — or run a free website audit.)

Frequently asked questions

How do you write good alt text? Describe what the image actually shows, accurately and concisely, so someone who can’t see it understands what’s there — for example, “golden retriever puppy sleeping on a blue blanket” rather than “dog.” Keep it brief, include a relevant keyword only where it fits naturally, avoid starting with “image of,” use an empty alt attribute for purely decorative images, and describe the function of images that are links or buttons.

What is the purpose of alt text? Alt text exists primarily for accessibility — it’s what screen readers announce to describe images to visually impaired users. It also helps search engines understand images they can’t see, which aids image SEO, and it displays if an image fails to load. Writing alt text for a human who can’t see the image first ensures it serves its main accessibility purpose, with the SEO benefit following naturally.

How long should alt text be? Alt text should be brief — a phrase or short sentence, roughly a sentence at most for typical images. Since screen readers read the entire alt text aloud, overly long descriptions become tiresome for users. Aim to convey the essential content and, if relevant, the function of the image in a few well-chosen words, rather than writing a lengthy paragraph.

Should I put keywords in alt text? Include a relevant keyword only where it genuinely fits the description of the image — that can help image SEO. But never force keywords or stuff them, since that helps no one and makes the alt text useless to screen-reader users. Describe the image accurately first; if a keyword is naturally part of that honest description, include it. Accurate description always takes priority over keyword placement.

Do decorative images need alt text? No — purely decorative images should have an empty alt attribute (alt=""), which tells screen readers to skip them so users aren’t bothered by meaningless descriptions. This is an important nuance: not every image needs descriptive alt text. Images that add information should be described, while purely decorative elements like background flourishes, dividers, or non-informative icons should be explicitly marked with empty alt text.

Should alt text start with “image of”? No. Screen readers already announce that the element is an image, so starting alt text with “image of” or “picture of” is redundant and wastes the listener’s time. Jump straight into the description instead. The exception is when the image type is meaningful — for example, beginning with “Diagram showing” or “Illustration of” when the format itself matters to understanding the content.

What alt text should a linked image have? For an image that’s also a link or button, the alt text should describe its function or destination rather than just its appearance. For example, a logo that links to the homepage might use alt text like “Launch with Bryan home,” and a button image might use “Download the free checklist.” For functional images, conveying what the image does is more useful than describing how it looks.

Written by Bryan Collins, SEO & AEO strategist. Want an accessible, well-optimized site? See website development work or run a free AI SEO audit.