How to Write Alt Text for Images: SEO and Accessibility Guide

Alt text is one of the smallest details on a webpage and one of the highest-impact. A single sentence under an image can make your content usable for blind and low-vision visitors, help Google understand what you're publishing, and improve how your visuals appear in search. Yet most sites still ship alt="image", leave alt empty, or paste keyword lists that help nobody.

This guide shows you how to write alt text that works for real people and for search, whether you're publishing blog posts, product photos, social graphics, or marketing landing pages. You'll see clear examples, common mistakes, and a faster workflow when you have dozens of images to ship.

What is alt text?

Alt text (alternative text) is the alt attribute on an <img> tag. Screen readers read it aloud so users who can't see the image still understand its content and purpose. Search engines also use it as a primary signal for what an image depicts.

Alt text is not a caption, not a file name, and not a place to dump hashtags or marketing slogans. It's a functional description: what is in the image, and why it matters on this page. If someone heard only the alt text, they should grasp the same point a sighted reader gets from looking at the picture in context.

Good alt text answers one question: if you couldn't see this image, what would you need to know?

Why alt text matters for accessibility

Roughly one billion people worldwide live with some form of disability, and millions rely on assistive technology to browse the web. When alt text is missing or useless, images become dead zones: a screen reader might say "image" or read a file name like IMG_4821.jpg, which communicates nothing.

Strong alt text is required for WCAG compliance and is simply good practice. It also helps people on slow connections who disable images, users with cognitive load who prefer text summaries, and anyone using voice control. Accessibility isn't a separate checklist item from quality content; it's part of publishing well.

• Describe information the image conveys, not just its category ("chart" vs what the chart shows)
• Match the tone and detail level of the surrounding article
• Use empty alt="" only for purely decorative images
• Don't start with "image of" or "picture of" unless the medium itself is relevant

Why alt text matters for SEO

Google's image SEO documentation recommends descriptive alt text for every meaningful image. Alt text helps Google index your visuals in Image Search, supports relevance for the page's main topic, and pairs with file names, compression, and structured data in a full image SEO strategy.

Alt text alone won't rank a thin page, but on a solid article or product page it's one of the easiest wins. For a deeper look at filenames, formats, and Core Web Vitals, read our complete image SEO guide. Fast pages matter too: heavy images slow load times, so compress assets with the Image Compressor before you publish.

Good vs bad alt text examples

The difference between helpful and harmful alt text is usually obvious once you see side-by-side examples.

Blog and editorial images

• Bad: alt="blog image"
• Good: alt="Screenshot of a color palette tool showing five blue shades labeled for web design"

E-commerce and product photos

• Bad: alt="shoe shoe running shoe buy now"
• Good: alt="White running shoe with orange sole, side view, on a gray background"

Charts, screenshots, and UI

• Bad: alt="graph"
• Good: alt="Bar chart showing email signups rising from 120 in January to 480 in June"

Social and marketing graphics

• Bad: alt="instagram post"
• Good: alt="Quote card with text: Start before you feel ready, on a teal gradient background"

Notice the pattern: good alt text is specific, factual, and tied to what's visible. Bad alt text is vague, repetitive, or stuffed with keywords that don't describe the pixels on screen.

How to describe images naturally

Write alt text the way you'd explain the image to a colleague on a quick call. Lead with the subject, add only the details that matter for this page, and stop when the message is clear.

1. Identify the subject: who or what is the focus?
2. Add context: action, setting, or data that the article references
3. Include text in the image: if a headline or label is essential, quote the key phrase
4. Skip redundant words: don't repeat the caption or the H2 right above the image
5. Stay under ~125 characters when possible, unless the image is complex (e.g. a detailed diagram)

For decorative flourishes (borders, stock textures, spacer graphics), use alt="" so assistive tech ignores them. For icons that act as buttons, describe the action ("Search", "Close menu"), not the icon shape.

Generate alt text with AI (Image Describer)

Writing alt text for ten images is manageable. Writing it for a hundred product SKUs, a migrated blog archive, or a weekly content calendar is not. That's where AI helps, as a draft machine, not a replacement for your judgment.

The Sounez Image Describer analyzes an uploaded image and suggests descriptive alt text you can edit before publishing. It runs in the browser, so your files aren't sent to a random third-party server. Use it to:

• Batch-describe product photos with consistent structure
• Get a first pass on screenshots and UI captures
• Reduce blank-alt gaps when you're under deadline

Always review AI output. Check names, numbers, colors, and whether the description matches why the image is on the page. Trim marketing language, fix mistakes, and align tone with your brand. Then compress the image with the Image Compressor so page speed doesn't undo your SEO work.

Frequently Asked Questions

How long should alt text be?

Aim for one concise sentence, usually under 125 characters. Long enough to convey what matters, short enough that screen readers don't drag on.

Should every image have alt text?

Every meaningful image needs descriptive alt text. Purely decorative images should use empty alt: alt="" so screen readers skip them.

Do keywords in alt text help SEO?

Yes, when they describe the image naturally. Google uses alt text for Image Search and page relevance. Keyword stuffing hurts more than it helps.

Is alt text the same as a caption?

No. Alt text is hidden metadata for accessibility and search engines. Captions are visible on the page and can add context, but they don't replace alt text.

Can AI write alt text for me?

AI tools like the Image Describer are a strong starting point. Always review the output for accuracy, tone, and whether it matches what the image actually shows.

Final thoughts: small text, big impact

Alt text takes seconds per image but compounds across every page you publish. Describe what viewers would miss, keep it human, and pair descriptions with a solid image SEO workflow. Use the Image Describer when you need speed, the Image Compressor for lean files, and our image SEO guide for the full picture. Your readers and Google will both notice the difference.