Image alt text explained: what we check & why it matters

What is image alt text?

Alt text (alternative text) is a text description set in an image's alt attribute:

<img src="dashboard-screenshot.jpg" alt="SEO audit dashboard showing 92 score with 3 critical issues highlighted" />

This text serves three distinct purposes:

• Accessibility: Screen readers read alt text aloud to visually impaired users. Without it, the screen reader either skips the image entirely or reads the filename (often meaningless like "IMG_4532.jpg").
• Fallback display: When an image fails to load (slow connection, broken URL, images disabled), the browser displays the alt text in its place.
• Search engine understanding: Google can't "see" images the way humans do. Alt text is the primary signal Google uses to understand image content for Google Images ranking and to assess the page's topical relevance.

Why alt text matters for SEO

Image alt text has a direct impact on search visibility:

• Google Images traffic: Google Images accounts for ~20% of all Google searches. Alt text is the primary ranking factor for image search results. Without it, your images won't appear in Google Images.
• Topical relevance: Google uses alt text as a content signal for the page itself — not just the image. Descriptive alt text reinforces what the page is about, contributing to topical relevance.
• Accessibility compliance: WCAG 2.1 Level A (the minimum standard) requires alt text on all non-decorative images. In many jurisdictions, this is a legal requirement — and Google has indicated that accessibility is an indirect quality signal.
• E-E-A-T signal: Descriptive, unique alt text is a quality signal. Stock photo alt text ("business meeting") or keyword-stuffed alt text is a negative signal.

How our engine checks alt text

We run one check that covers all images on the page:

Check: Images missing alt text

ID: onpage-image-alt-missing
Severity: Warning
Scope: Per page
Logic: We find every <img> element on the page and check its alt attribute. If the alt attribute is missing entirely (<img src="..."> with no alt) or empty (alt="" with only whitespace), the image is flagged. The check fails if one or more images have missing alt text. We report the count and the src URLs of the offending images.

Why we flag it: Every content image should have descriptive alt text. A page with 10 images and 3 missing alt attributes is leaving SEO value on the table — those images won't rank in Google Images, screen reader users get a broken experience, and the page loses topical relevance signals.

Note on decorative images: Truly decorative images (borders, spacers, icons that repeat adjacent text) should use alt="" (empty string, not missing). Our engine currently flags empty alt the same as missing alt — if you know an image is decorative, you can safely ignore the flag for that image.

How to read your alt text result

When you run a URL through our free checker, the alt text check shows:

• Pass (green): All images on the page have non-empty alt text. No action needed.
• Warning (yellow): One or more images are missing alt text. The report shows how many and lists their source URLs so you can identify each image.

How to write good alt text

• Be specific and descriptive: "Red Nike running shoe, side view" is better than "shoe" or "product image."
• Keep it concise: 5–15 words, under 125 characters. Screen readers read the entire alt text without pausing.
• Include relevant keywords naturally: If the image shows your product, mention the product name. But don't stuff keywords — "SEO tool SEO checker SEO analyzer free SEO" is spam.
• Don't start with "image of" or "picture of": Screen readers already announce it as an image. Starting with "image of" is redundant.
• Describe the content, not the function: For a chart, describe what the chart shows ("Monthly traffic growth from 1,000 to 15,000 visits"), not that it's a chart.

How to fix alt text issues (by platform)

We have step-by-step fix guides for adding alt text on every major CMS:

• Fix missing image alt text in WordPress →
• Fix missing image alt text in Shopify →
• Fix missing image alt text in Webflow →

Alt text and AI visibility

AI retrieval systems increasingly process multimodal content — text, images, and their relationships. Alt text helps these systems understand what an image contributes to the page's content. When an AI system retrieves your page to answer a query, descriptive alt text ensures image-heavy content (infographics, diagrams, screenshots) can be understood and cited accurately.

For more on AI citation optimization, see our How to get cited by ChatGPT, Perplexity & Claude guide.

FAQ

What is image alt text?

Alt text is the text description set in an image's alt attribute. It's read by screen readers, displayed when images fail to load, and used by search engines to understand image content for ranking.

Does alt text affect SEO rankings?

Yes. Alt text is the primary way search engines understand image content. It directly affects Google Images rankings and contributes to the page's topical relevance signal.

How long should alt text be?

Alt text should be concise but descriptive — typically 5–15 words (under 125 characters). Describe what the image shows without keyword stuffing or starting with "image of."

Should decorative images have alt text?

Decorative images should have an empty alt attribute (alt="") — not a missing alt attribute. An empty alt tells screen readers to skip the image entirely.