What is alt text?
Why alt text is an accessibility feature first and image SEO second, how to write it well, and why decorative images take an empty alt attribute.
Alt text — short for alternative text — is a written description of an image, added in the HTML so it can stand in for the image when the image itself cannot be seen. It is read aloud by screen readers, shown when an image fails to load, and used by search engines to understand what a picture depicts. Its first job is accessibility; its second is image SEO, and the two mostly pull in the same direction.
What it looks like
Alt text is the alt attribute on an image tag:
<img src="golden-retriever-puppy.jpg" alt="A golden retriever puppy sitting in long grass" />
When the image loads, a sighted visitor sees the picture and never the alt text. When it fails to load, or when a screen reader encounters it, the alt text is what conveys the image’s meaning. That is the mental model to write from: what would someone need to hear to get the same information the image carries?
Why it matters for accessibility
People who use screen readers rely on alt text to know what an image shows. An image with no alt attribute is announced only as “image”, or the screen reader reads the file name — IMG_4821.jpg — which tells them nothing. For images that carry real information, missing or empty alt text is a genuine barrier, and in many jurisdictions it is also a legal accessibility requirement, not merely a nicety.
Why it matters for SEO
Search engines cannot see the content of an image the way a person does, so alt text is one of the main signals they use to understand what the image depicts and whether it is relevant to a search. That helps the image rank in Google Images, and it adds context to the page around it. The effect is real but modest — alt text will not carry a weak page — and it is strongest when the description genuinely matches both the image and the page it sits on.
Decorative images take empty alt text
Not every image needs a description. Purely decorative images — background textures, dividers, spacer graphics that add nothing informational — should have an empty alt attribute: alt="". That is not the same as omitting the attribute. An empty alt tells a screen reader to skip the image entirely, which is correct for decoration; omitting it entirely can cause the screen reader to fall back to reading the file name. The distinction matters: describe informational images, and explicitly silence decorative ones.
How to write good alt text
Describe the content and its function. If the image is a chart, state what it shows, not just “chart”. If it is a link or a button, describe where it goes. Be concise. A sentence is usually plenty; screen-reader users do not want a paragraph per image. Skip “image of” and “picture of”. The screen reader already announces that it is an image, so those words just waste the listener’s time. Let context guide detail. The same photo needs different alt text on a photography portfolio than in a news article — describe what matters here.
The mistakes
Missing alt text on informational images is the most common and the most consequential — it fails accessibility and gives search engines nothing to work with. Keyword stuffing — cramming search terms into the alt attribute — is the mistake that backfires hardest: it makes the description useless to a screen-reader user and looks manipulative to Google. Describing decorative images clutters the experience for screen-reader users, who have to listen to descriptions of things that carry no meaning. Relying on the file name instead of alt text — a descriptive file name helps a little, but it is no substitute for a proper description.
How to check yours
Our alt text checker scans a page for images and reports which ones are missing alt text, which have empty alt attributes, and which look like file names rather than descriptions — so you can see at a glance where the gaps are before fixing them. To review images alongside the rest of your on-page setup across the whole site, run a full site check, or see how to check if a website is SEO friendly for where image accessibility fits among the other basics.
Frequently asked questions
- What is alt text?
- Alt text, or alternative text, is a written description of an image added in the HTML alt attribute. It stands in for the image when the image cannot be seen — read aloud by screen readers, shown when an image fails to load, and used by search engines to understand what the picture depicts. Its primary purpose is accessibility, with image SEO as a secondary benefit.
- Does alt text help SEO?
- Yes, modestly. Search engines cannot see an image's content directly, so alt text is a main signal for understanding what it shows and whether it is relevant, which helps it rank in Google Images and adds context to the surrounding page. The effect is real but limited — it will not lift a weak page — and it is strongest when the description honestly matches both the image and the page.
- How do I write good alt text?
- Describe what the image shows and what it does, as if explaining it to someone who cannot see it. Keep it to about a sentence, skip 'image of' and 'picture of' since the screen reader already announces it is an image, and let the page's context decide what detail matters. Write for the person first, and the SEO benefit follows without any keyword forcing.
- Should decorative images have alt text?
- They should have an empty alt attribute — alt="" — rather than a description or no attribute at all. An empty alt tells a screen reader to skip the image, which is correct for purely decorative graphics like textures or dividers. Omitting the attribute entirely is worse, because some screen readers then read the file name aloud instead of skipping the image.
- Is keyword stuffing alt text bad?
- Yes, it is the worst approach. Cramming search terms into the alt attribute makes the description useless to screen-reader users, who rely on it to understand the image, and it reads as manipulative to search engines. Alt text that honestly describes the image already contains the relevant terms naturally, so stuffing adds nothing and risks looking like spam.
- What is the difference between alt text and a caption?
- A caption is visible text displayed near the image for everyone to read, while alt text is in the HTML and surfaces only when the image cannot be seen. They serve different purposes and can coexist: a caption adds context for all readers, and alt text ensures screen-reader users and search engines still understand the image. A caption does not replace the need for alt text.