Missing Alt Text: The SEO Quick Win You're Ignoring
Alt text tells screen readers what an image shows and gives search engines context they can't get from pixels alone. Most sites are missing it on dozens of images.
Alt text (short for alternative text) is a text description added to an image's HTML tag via the alt attribute. Most people call it an "alt tag", which is fine: strictly it is an attribute on the <img> tag, but alt tag, alt attribute and alt text all mean the same thing. It serves two purposes: it tells screen readers what an image shows, and it gives search engines context they can't get from pixels alone.
Most sites have dozens or hundreds of images missing alt text. Fixing them takes minutes per image, costs nothing, and delivers measurable improvements in both accessibility compliance and search visibility.
Quick reference: what alt to write
| Situation | What to put in the alt |
|---|---|
| Informative photo or illustration | A short, specific description of what it shows in this context |
| Product image | The product name plus the detail that matters (colour, angle, variant) |
| Image that is a link or button | Where the link goes or what the button does, not what the picture looks like |
| Logo | The organisation's name (add "home" if it links to the homepage) |
| Chart, diagram or infographic | A one-line summary in the alt, with the full detail in the surrounding text or a caption |
| Image of text | The text itself, word for word |
| Purely decorative image | An empty alt: alt="" |
| Image already described by the text next to it | An empty alt: alt="", so the description is not read twice |
Why alt text matters
Accessibility is the primary reason
Screen readers - used by people who are blind or have low vision - rely on alt text to describe images. Without it, a screen reader either skips the image entirely or reads out the filename, which is usually meaningless (e.g., "DSC_0042.jpg" or "hero-banner-v3-final.png").
Web Content Accessibility Guidelines (WCAG) require alt text on all informative images. In many jurisdictions, this is also a legal requirement under disability discrimination laws.
SEO is a secondary benefit
Google can't see images the way humans do. Alt text is the primary signal Google uses to understand what an image depicts and whether it's relevant to a search query. Images with descriptive alt text can rank in Google Images - a traffic source most sites ignore. For e-commerce, Google Images drives purchase-intent clicks directly to product pages.
How to write good alt text
Be descriptive and specific
Describe what the image actually shows, not what you wish it showed. "A golden retriever catching a frisbee in a park" is useful. "Dog" is not. The test: could someone who can't see the image understand what it contributes to the page?
Keep it concise
Aim for one to two sentences, roughly 125 characters or fewer. Screen readers read alt text in a continuous stream - long descriptions become exhausting to listen to. If an image needs a longer explanation, use a caption or aria-describedby instead.
Don't stuff keywords
Writing alt text purely for search engines defeats the purpose and can trigger spam filters. "Buy cheap running shoes best running shoes discount running shoes" is not alt text - it's keyword spam. Describe the image naturally and relevant keywords will appear on their own.
Decorative images
Not every image needs a description. Purely decorative images - background patterns, spacer graphics, visual flourishes - should use an empty alt attribute: alt="". This tells screen readers to skip the image entirely. Omitting the alt attribute altogether is different and worse - the screen reader may fall back to reading the filename.
Common mistakes
- Using the filename as alt text. "IMG_4392.jpg" tells nobody anything. CMS platforms sometimes auto-fill alt from the filename - always review it.
- Starting with "image of" or "picture of". Screen readers already announce the element as an image. Writing "Image of a sunset" results in the user hearing "Image: image of a sunset" - redundant and distracting.
- Making it too long. Alt text much over 125 characters is tiring to listen to and loses impact. If the image is complex (a chart, infographic, or diagram), put the detailed description in the surrounding text instead.
- Leaving the attribute off entirely. Missing
altis worse than emptyalt="". Without the attribute, assistive technology has to guess, often reading a garbled URL path.
Finding missing alt text
Manually inspecting every image on a large site is tedious. An automated scanner can crawl your pages, flag every <img> tag missing the alt attribute, and report each image URL so you can fix them systematically. Prioritise images above the fold and on high-traffic pages first.
To check a single page right now, run it through the free alt text checker. It lists every image with a missing alt tag, treats alt="" as a valid decorative image rather than an error, and also lists alt text worth reviewing: filenames used as alt, alt text over 125 characters, and the same alt repeated across images.
Alt text FAQs
Is an alt tag the same as alt text?
Yes. "Alt tag" is the everyday name, "alt attribute" is the technical one, and "alt text" is the value it holds. Whichever term you use, you are talking about the alt attribute on an <img> element.
Does every image need alt text?
Every image needs an alt attribute, but not every image needs a description. Informative images need descriptive alt text; decorative images need an empty alt="" so screen readers skip them. The only wrong answer is leaving the attribute off.
How long should alt text be?
Aim for roughly 125 characters or fewer. If an image needs a longer explanation, such as a chart, summarise it in the alt and put the detail in a caption or the surrounding text.
Does alt text help SEO?
Yes, mainly for image search. Alt text is one of the clearest signals Google has about what an image shows, so descriptive alt text helps images rank in Google Images and adds context to the page around them.
How do I check alt text across a whole site?
Use a site-wide audit that crawls your pages and lists every image missing alt text in one report, then fix the highest-traffic pages first. To spot-check a single page, the free alt text checker is quicker.
AuditZap scans your pages and flags every image without an alt attribute, so you can fix accessibility gaps and unlock Google Images traffic.