What Is Image Alt Text?
Alt text (alternative text) is the text description added to an image's HTML tag using the alt attribute, for example <img src="photo.jpg" alt="Description of the image">. It serves as a text alternative when the image cannot be displayed and is read aloud by screen readers for visually impaired users. Search engines also rely on alt text to understand what an image depicts since they cannot interpret images the way humans do.
Why Alt Text Matters for SEO
Alt text is a key factor in image search rankings. Google Images is one of the largest search engines in the world, and well-written alt text helps your images appear in relevant image searches, driving additional traffic to your site. Alt text also provides context to search engine crawlers about how an image relates to the surrounding content, which can strengthen the topical relevance of the page.
Beyond SEO, alt text is a legal accessibility requirement under regulations like the Web Content Accessibility Guidelines (WCAG). Missing alt text can make your site inaccessible to users who rely on screen readers.
Alt Text Best Practices
| Guideline | Recommendation |
|---|---|
| Be descriptive | Describe what the image shows in a concise, specific way. "Red mountain bike on a forest trail" is better than "bike". |
| Keep it concise | Aim for under 125 characters. Screen readers may cut off longer descriptions. |
| Include keywords naturally | If the image is relevant to your target keyword, include it naturally in the alt text. Do not force it. |
| Avoid "image of" or "photo of" | Screen readers already announce the element as an image. Starting with "image of" is redundant. |
| Decorative images | Purely decorative images (borders, spacers) should use an empty alt attribute: alt="". |
| Every image needs alt | All <img> tags should have an alt attribute, even if it is empty for decorative images. |
Common Alt Text Mistakes
- Missing alt attribute - The most common issue. Images with no alt attribute at all fail accessibility checks.
- Empty alt on meaningful images - Using
alt=""on images that convey information hides them from screen readers. - Generic alt text - Descriptions like "image", "photo", or "IMG_3842.jpg" provide no useful context.
- Keyword stuffing - Cramming keywords into alt text makes it unnatural and can be flagged as spam.
- Identical alt text on every image - Each image should have a unique description that reflects its specific content.
How RankNibbler Checks Your Image Alt Text
RankNibbler scans every <img> tag on your page and checks whether each image has an alt attribute. Images with missing or empty alt text are flagged in the audit results, along with the image source URL so you can identify which images need attention. The total count of images with and without alt text is included in your SEO score.
Scan your images now. Visit the RankNibbler homepage and enter a URL to check your alt text.