Turn off images in your browser for a minute and load a page full of photos. What you’ll see is a scatter of empty boxes, each with a little caption where the picture should be. That caption is the alt text, and the gap you just experienced is exactly what a blind visitor relying on a screen reader, or a search engine crawler that can’t “see,” navigates every single day. Alt text is a small attribute that quietly does three big jobs.
What alt text is
Alt text (short for “alternative text”) is a written description added to an image in a page’s HTML, using the alt attribute on the img tag. It exists to communicate the content and purpose of an image to anyone, or anything, that can’t view the image itself. That includes people using screen readers, browsers that fail to load the image, and the bots that crawl and index the web.
In code it looks like this:
<img src="golden-retriever-puppy.jpg" alt="A golden retriever puppy chewing a tennis ball on a lawn">
That one attribute is the whole mechanism. The skill is in writing it well.
The three jobs alt text does
Accessibility
This is the original and most important reason alt text exists. Screen readers read the alt text aloud, so a visually impaired user understands what an image shows and why it’s there. Without it, they get “image” or a meaningless filename, and the content falls apart. Accessibility law in many regions, including standards tied to the ADA and WCAG, treats meaningful alt text as a baseline requirement, not a nice-to-have.
SEO
Search engines can’t truly look at a photo the way a person does; they lean on surrounding context and the alt text to understand what an image depicts. Good alt text helps your images surface in image search and gives the page additional relevance signals. From our agency experience, image search is one of the most overlooked traffic sources out there, and clean alt text is the cheapest way to start tapping it.
Fallback when images break
Slow connections, broken links, and blocked images happen. When an image fails to load, the browser displays its alt text in place of the empty box, so the visitor still gets the gist instead of a confusing blank.
How to write alt text that actually works
Most bad alt text fails in one of two directions: it’s empty, or it’s stuffed with keywords. The sweet spot is a brief, accurate description of what matters about the image in context.
- Be specific but concise. Describe what’s actually in the image. Aim for a short phrase, not a paragraph; screen readers read every word aloud, so rambling descriptions punish the people the attribute is meant to help.
- Skip “image of” and “picture of.” Screen readers already announce that it’s an image. Lead straight into the description.
- Write for context, not in a vacuum. The same photo of a chart might need different alt text on a finance page than on a design portfolio. Describe what’s relevant to this page.
- Don’t keyword-stuff. Cramming target keywords into alt text reads as spam to both screen readers and search engines. Include a keyword only if it genuinely describes the image. When we run this for clients, the rule is simple: write the description first, and if a keyword fits naturally, great; if not, leave it out.
- Use empty alt text for purely decorative images. If an image carries no information, a background flourish, a spacer, a decorative divider, give it
alt="". That tells screen readers to skip it cleanly instead of reading out a distracting filename.
A quick before-and-after
Say you have a photo of a barista pouring latte art. Weak alt text: “coffee image best coffee shop SEO coffee near me.” That helps nobody and looks like spam. Strong alt text: “Barista pouring a leaf pattern into a latte at a café counter.” It’s accurate, it’s useful to a screen reader, and it still naturally contains the kind of language someone might search for. What we consistently see is that writing for the human first produces better SEO than writing for the crawler.
Frequently asked questions
Does every image need alt text?
Every meaningful image does. Images that convey information, content, or function should always have descriptive alt text. Purely decorative images should get empty alt text (alt="") so screen readers skip them rather than reading out a filename.
How long should alt text be?
Short. A concise phrase that captures what matters is ideal. There’s no hard limit, but if you’re writing a long sentence or two, the image may be complex enough to warrant a fuller description elsewhere on the page, with the alt text kept brief.
Is alt text a ranking factor?
It’s a contributing signal, not a magic lever. It helps search engines understand your images and is essential for ranking in image search, but it works as part of overall on-page relevance, not as a standalone trick.
What’s the difference between alt text and a caption?
A caption is visible to everyone and appears near the image as supplementary information. Alt text is in the HTML, hidden from sighted users in normal viewing, and exists specifically for screen readers, crawlers, and load-failure fallback. The two serve different purposes and can coexist.
Related terms
- Visual Content — the images and graphics that alt text makes accessible and indexable.
- Organic Traffic — the search visitors well-optimized image alt text can help attract.
- Image Optimization — the broader practice of making images fast, accessible, and search-friendly.
- On-Page SEO — the set of page-level signals, alt text included, that influence rankings.
- Web Accessibility — the inclusive-design discipline that alt text is a core part of.
- Meta Description — another behind-the-scenes HTML attribute that shapes how content is understood and surfaced.
