Image Alt Text: What It's For, and How to Write It Right
Alt text does two jobs at once: it's what a screen reader announces instead of the image, and one of the few signals Google has for what an image actually shows. Here's how to get both right.
Alt text does two jobs at once
The alt attribute on an <img> tag exists for one reason: to describe the image to whoever or whatever can't see it. That covers two real audiences — a screen reader announcing the page to a visually impaired visitor, and a search engine that can read every word of surrounding text but genuinely cannot interpret pixels. It also quietly does a third job: if the image fails to load, the alt text is what shows in its place instead of a broken-image icon.
What makes alt text good versus useless
Good alt text describes what's actually relevant about the image in plain language — "golden retriever puppy sitting in autumn leaves," not "image of a dog." The "image of" or "picture of" prefix is redundant; screen readers already announce that it's an image before reading the alt text. For purely decorative images — a background texture, a divider line — the correct move is an empty alt="", not a missing attribute. An empty alt tells a screen reader to skip the image silently; a missing one often makes it announce the filename instead.
Paste a URL into CheckSEO's Image Alt Checker to find every image missing alt text on a page — no signup.
Check your page for missing alt text5 alt text mistakes that undercut both SEO and accessibility
Missing alt text entirely
The single most common finding on any audit. Every meaningful image needs one — a screen reader falls back to reading the filename, which is rarely useful to anyone.
Keyword-stuffed alt text
Writing "running shoes buy cheap running shoes sale" instead of a real description is the image equivalent of the keyword stuffing that hurts written content — it reads as spam to both a screen reader user and Google's quality systems.
Generic, unhelpful descriptions
"image1234.jpg," "photo," or "banner" technically fills the attribute but describes nothing. If the alt text wouldn't help someone picture the image, it isn't doing its job.
No empty alt for decorative images
A spacer GIF or a purely ornamental icon still needs an alt="" — leaving the attribute off entirely forces assistive tech to guess whether it was an oversight or intentional.
Alt text that just repeats the caption
If a visible caption already says "Q3 revenue chart," identical alt text adds nothing — use the alt text to describe what the image actually shows instead (the trend, the key numbers) that the caption doesn't.
The accessibility angle isn't optional
Missing alt text is one of the most common findings in web accessibility lawsuits, and WCAG 2.1 — the standard most accessibility regulations reference, including the ADA in the US — explicitly requires text alternatives for meaningful images. This isn't a nice-to-have layered on top of SEO; for many businesses it's a genuine legal exposure sitting in plain sight on every product photo and hero image.
Check your own page
CheckSEO's Image Alt Checker scans a page and lists every image missing alt text in one pass, so you're not opening dev tools on every image by hand.
Frequently asked questions
What is image alt text?
A short text description added to an image's HTML attribute that stands in for the image when it can't be seen — read aloud by screen readers, shown if the image fails to load, and used by search engines that can't otherwise interpret what's in a picture.
Is image alt text important for SEO?
Yes, though indirectly — it's the main signal Google has for what an image depicts, which affects image search visibility and gives the page slightly more relevant text for search engines to read.
When should alt text not be used for an image?
For purely decorative images that add nothing informational — a background pattern or a divider graphic — use an empty alt attribute (alt="") rather than skipping it entirely. That tells a screen reader to skip the image silently instead of announcing a meaningless filename.
Is alt text legally required?
In many jurisdictions, yes in practice — accessibility laws like the ADA (US) and similar regulations elsewhere have been applied to websites, and missing alt text is one of the most common findings in accessibility lawsuits. WCAG 2.1, the standard most of these laws point to, requires it for meaningful images.
How long should alt text be for images?
Long enough to describe what's actually relevant, typically under about 125 characters — screen readers can cut off longer text, and Google doesn't need more than a concise, accurate description.
Check your own site with the Image Alt Checker.
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