Image alt tags are the short text descriptions you add to an image’s HTML so screen readers can announce it and search engines can read what they can’t see. Done well, alt text earns traffic from Google Images, reinforces a page’s topical relevance, and keeps the page usable when an image fails to load. Done badly — stuffed with keywords or left blank on meaningful images — it does nothing for SEO and actively hurts users.
Image Alt Tags
Image alt tags (the alt attribute) are short text descriptions added to an image’s HTML that convey the image’s content and function for screen readers, supply fallback text when the image fails to load, and give search engines readable text to understand and index the image.
What alt text actually does
Search engines have gotten remarkably good at recognizing what’s in an image, but they still lean on the surrounding text and the alt attribute to decide what the image means in context. The alt attribute does three jobs at once, and they reinforce each other:
- Accessibility. Screen readers announce the alt text in place of the image, so a user who can’t see the screen still gets the content.
- Fallback. When the image fails to load — slow connection, broken path, blocked CDN — the browser renders the alt text where the image would have been.
- SEO. It’s the primary text signal Google uses to understand and rank an image in Google Images and Discover, and it feeds the page’s overall topical relevance.
Here’s the part most “tips” articles get wrong: there is no Google ranking penalty for missing or imperfect alt text, and no penalty for failing an accessibility check. Google has said plainly that alt text helps it understand images — its absence is a missed opportunity, not a demerit. The “accessibility penalty” you’ll read about elsewhere is a myth. The real cost of bad alt text is lost image-search traffic and an unusable experience for assistive-technology users, which is reason enough to get it right.
What the markup looks like
Alt text lives in the alt attribute on the <img> element. A good one describes the subject, and — where it matters — the action and context:
<!-- Informative image: describe subject + context -->
<img src="/img/blue-running-shoes.jpg"
alt="Blue Nike running shoes on a wooden gym floor">
<!-- Functional image (a link/button): describe the action, not the icon -->
<a href="/cart"><img src="/icons/cart.svg" alt="View shopping cart"></a>
<!-- Decorative image: empty alt so screen readers skip it -->
<img src="/img/divider.svg" alt="">The difference between alt="" and no alt attribute at all matters. An empty alt="" tells assistive tech “skip this, it’s decorative.” A missing attribute makes some screen readers read out the file name (blue-running-shoes-final-v2.jpg), which is worse than silence.
Why alt tags matter for SEO
Alt text gives crawlers indexable, contextual text for content they otherwise can’t parse. The practical payoffs:
- Image-search and Discover traffic. Optimized alt text is the main lever for ranking in Google Images — a real, often-overlooked acquisition channel for product, recipe, how-to, and visual-query pages.
- Topical reinforcement. Alt text that naturally echoes the page’s focus keyword and semantic context strengthens the page’s relevance signal without you adding visible body copy.
- Rich-result eligibility. Well-described images pair with structured data (product, recipe, article) to support image-bearing rich results in the SERP.
- Resilience. When an image 404s or a CDN hiccups, the fallback alt text preserves meaning and keyword context instead of leaving a blank box.
In the AI-Overviews era, images are increasingly pulled into generative answers and visual results. Clear, factual alt text is part of how a model figures out which image answers a query — another reason to describe, not decorate-and-stuff.
How to write alt text that works
The whole skill is “describe the image as if reading it aloud to someone who can’t see it, then check that it fits the page.” Concretely:
- Be specific. Name the subject, the action, and the details that matter to the page. “Golden retriever puppy chewing a rope toy” beats “dog.”
- Include the keyword only when it’s honest. One natural keyword is fine if it genuinely describes the image. Forced phrases are keyword-stuffing — ignored at best, a quality smell at worst.
- Don’t repeat the caption or nearby text. Make the alt complementary, not redundant. If the caption already says it, the alt can add the part the caption left out.
- Keep it tight. Aim for a short phrase — roughly 125 characters or fewer, which is where many screen readers truncate. If an image needs a paragraph, that paragraph belongs in the body copy.
- Match the image’s role. For functional images (a clickable icon or button), describe the action (“Download PDF”), not the picture of the icon.
- Use
alt=""for purely decorative images. Background flourishes, spacers, and ornamental dividers should be skipped by assistive tech.
Alt text vs. the other “image text” fields
People routinely confuse alt text with file names, captions, and title attributes. They are not interchangeable:
| Field | Who reads it | SEO weight | When to use |
|---|---|---|---|
alt attribute | Screen readers, search engines, fallback rendering | High — primary image signal | Always, on every informative or functional image |
| Image file name | Search engines (minor) | Low–moderate | Use descriptive, hyphenated names (blue-running-shoes.jpg) |
Caption (<figcaption>) | All users, on-page | Moderate — read by everyone | When extra visible context helps the reader |
title attribute | Hover tooltip only | Negligible | Rarely — it’s not a substitute for alt text |
A useful pre-publish check: skim a page with images turned off (or read only the alt attributes in the HTML). If the page still makes sense and each image’s purpose is clear, your alt text is doing its job. This is the same kind of pass we run during a broader SEO content audit.
Good vs. bad alt text
| Image | Weak alt text | Strong alt text |
|---|---|---|
| Product photo | alt="shoes" | alt="Blue Nike Pegasus running shoes, side view" |
| Chart in a blog post | alt="seo seo ranking keywords graph 2026" | alt="Line chart showing organic traffic up 38% over six months" |
| Cart icon link | alt="icon" | alt="View shopping cart" |
| Decorative divider | alt="divider line image decorative" | alt="" |
Where alt text fits in the bigger picture
Alt text is a small, high-leverage piece of on-page SEO — cheap to get right, easy to neglect at scale. At a few dozen images it’s a manual habit; at thousands of programmatic pages, it’s a templating and QA problem. On large catalogs we generate alt text from structured product data and spot-check samples, the same engineering-first approach behind our programmatic SEO work. Either way, the principle holds: describe the image honestly, serve the user first, and the search benefit follows.
Frequently Asked Questions
Do image alt tags help SEO?
Yes. Alt text is the primary text signal search engines use to understand and rank images, so it’s the main lever for earning traffic from Google Images and Discover. It also reinforces a page’s topical relevance and acts as fallback content when an image fails to load. It won’t rank a page on its own, but it’s high-leverage and cheap.
Is there an SEO penalty for missing alt text?
No. Google does not penalize pages for missing or imperfect alt text, and there is no separate “accessibility penalty.” Missing alt text is a missed opportunity — lost image-search traffic and a worse experience for screen-reader users — rather than a ranking demerit. The real cost is usability and forfeited image visibility, not a Google sanction.
How long should alt text be?
Keep it to a short, descriptive phrase — roughly 125 characters or fewer, which is where many screen readers truncate. Describe the subject, the relevant action, and key details, then stop. If an image genuinely needs a paragraph of explanation, that explanation belongs in the visible body copy, not crammed into the alt attribute.
What’s the difference between alt text and a caption?
Alt text lives in the alt attribute and is read by screen readers and search engines, or shown when the image fails to load. A caption (<figcaption>) is visible to everyone on the page. Use captions for context that helps all readers, and alt text to describe the image itself — keep them complementary, not duplicates.
Should decorative images have alt text?
No — use an empty alt="" attribute so assistive technology skips them. Spacers, ornamental dividers, and background flourishes add nothing to the content, so announcing them just clutters the experience. Note that empty alt="" is different from omitting the attribute entirely, which can make some screen readers read out the file name instead.