How to Write Effective Alt Text for Images: An SEO Guide

Alt text — the alternative text attribute on HTML image elements — is one of the most consistently misunderstood elements in SEO. Many site owners either leave it blank, fill it with keyword repetitions, or write vague descriptions that serve neither users nor search engines. Getting alt text right is a straightforward win that improves accessibility, helps images rank in Google Image Search, and contributes to overall on-page keyword signals.

What Alt Text Does

Alt text serves two primary purposes that work together rather than separately.

Accessibility. Screen readers — software used by visually impaired users to navigate the web — read alt text aloud when they encounter an image. For users who cannot see images, alt text is the only way to understand what an image contains. This is not an optional consideration — in many jurisdictions, web accessibility is legally required for certain types of sites, and even where it is not legally mandated, inclusive design is a professional and ethical standard.

Search engine understanding. Search engines cannot see images the way humans can — they rely on surrounding text, file names, and alt text to understand what an image depicts. Well-written alt text helps Google index your images in Image Search, contributes keyword relevance signals to the page's overall context, and as we covered in our guide to image SEO, descriptive filenames and alt text together determine how well an image ranks.

How to Write Good Alt Text

Be specific and descriptive. Alt text should describe exactly what the image shows. "Photo of a website" is useless. "Broken link checker tool showing a list of 404 errors found on a sample website" is excellent. The test: if a sighted person read your alt text aloud, would a blind person have an accurate mental picture of the image?

Include your target keyword naturally where it genuinely describes the image. If your page is about broken link building and an image shows a broken link checker tool in action, alt text that includes "broken link checker" is natural and appropriate. Do not force keywords into alt text where they do not genuinely describe the image — "broken link checker SEO tool 2026 find dead links" is keyword stuffing, not description.

Keep it concise. 125 characters or fewer is the recommended maximum. Longer descriptions may be truncated by screen readers. If an image genuinely requires a longer description — a complex chart or infographic — provide a brief alt text and a longer description in the surrounding text or a linked figure caption.

Do not start with "image of" or "picture of". Screen readers already announce that they are describing an image. Starting alt text with "image of" is redundant and wastes your character allowance.

When to Use Empty Alt Text

Decorative images — images that add visual design but contain no informational content — should have empty alt text: alt="". This explicitly tells screen readers to skip the image, avoiding noise for visually impaired users. Examples of decorative images include background patterns, decorative borders, and purely aesthetic flourishes.

Do not omit the alt attribute entirely for decorative images — a missing alt attribute is treated as missing information, while alt="" explicitly signals that the image is decorative.

Alt Text for Linked Images

When an image functions as a link (clickable logo, button image), the alt text should describe the link destination rather than the image itself. A company logo that links to the homepage should have alt text like "[Company Name] homepage" rather than "[Company Name] logo".

Auditing Your Alt Text

Use the free SEOLinkScan Site Scanner to crawl your site and identify images with missing or empty alt text. Combine this with a review of your most important pages — particularly product pages, service pages, and your highest-traffic articles — to ensure all significant images have meaningful alt text that contributes to the page's keyword context. As we covered in our guide to on-page SEO, alt text is part of the complete on-page optimisation process that should be applied to every published page.