Alt text (alternative text) is a short written description of an image, added in the HTML alt attribute. Screen readers read it aloud to visually impaired users, browsers show it when an image fails to load, and search engines use it to understand what the image shows. It is part of on-page SEO and basic web accessibility.
<img src="oak-garden-bench.webp" alt="Three-seater oak garden bench on a stone patio" width="1200" height="800">
How to write good alt text
- Describe what is in the image as you would to someone on the phone.
- Be specific: “Golden retriever puppy chewing a red rope toy” beats “dog”.
- Keep it under about 125 characters.
- Include a keyword only when it fits naturally.
- Skip “image of” or “picture of”. Screen readers already announce it is an image.
- Use empty alt (alt=””) for purely decorative images so screen readers skip them.
Bad vs good examples
- Bad:
alt="shoes shoes running shoes buy shoes cheap" - Bad:
alt="IMG_4823" - Good:
alt="Woman running on a forest trail in blue waterproof trail shoes" - Chart:
alt="Bar chart showing organic traffic rising from 2,000 to 9,500 visits between January and June"
Beyond alt text: full image SEO
File names
Rename files before uploading: oak-garden-bench.webp tells Google more than DSC_0042.jpg.
Compression and format
Large images are the most common cause of slow pages. Use WebP or AVIF, resize to the display size and compress. This directly improves the LCP score in Core Web Vitals.
Dimensions
Always set width and height attributes so the browser reserves space and the layout does not jump.
Lazy loading
Add loading=”lazy” to images below the fold, but never to the main hero image.
Context
Google also reads the text around an image, the caption and the page title. Place images next to relevant text.
Original images
Your own photos and diagrams stand out in image search and support signals of real experience. Stock images that appear on thousands of sites add nothing unique.
Image sitemaps and structured data
Most WordPress SEO plugins add images to the XML sitemap automatically. Product, recipe and article schema markup can include image properties that help rich results.
Frequently asked questions
Does alt text help rankings?
It helps image search rankings and gives a small relevance signal to the page. Its main purpose is accessibility.
Should every image have alt text?
Every meaningful image, yes. Decorative images should have an empty alt attribute.
Related terms
See header tags, ecommerce SEO and the SEO encyclopedia.
Mr. SEO
Mr. SEO is the webmaster at SEO TT - SEO tips and tricks, a publication about all things SEO related.