Image Alt Text SEO — How to Write It and Why It Matters

What Alt Text Does

For SEO: Google's image indexing pipeline reads alt text as the primary text signal for what an image depicts. An image with no alt text can't rank in Google Image Search. An image with accurate, descriptive alt text can drive additional traffic via image search.

Beyond Image Search, alt text reinforces a page's topical signals. If an article about "broken link building" includes images with alt text describing broken links, link building tools, and example reports, the page's topical relevance is stronger. Each image becomes a small additional signal that the page is genuinely about the topic it claims to cover.

For accessibility: Screen readers read alt text aloud to visually impaired users. Meaningful alt text makes images understandable to everyone. Missing alt text causes screen readers to either skip the image entirely or fall back to reading the filename (e.g., "IMG_2847.jpg"), which provides no useful context and interrupts the reading experience.

How to Write Effective Alt Text

Be specific. Describe what's actually in the image. "Screenshot of the Link Checker results table showing 3 broken links on example.com" is better than "link checker screenshot." The more accurately the text describes the image, the more useful it is to both screen reader users and Google's image indexer.

Include the natural keyword where it fits. If an image illustrates a concept you're writing about, the keyword often fits naturally. "Diagram showing redirect chain with three hops causing a loop" naturally includes "redirect chain." Don't force it — if the keyword doesn't fit the image description, leave it out. Relevance should come from accuracy, not from insertion.

Keep it concise. 125 characters is the practical limit (beyond which most screen readers truncate). Most good alt text is under 80 characters. Don't write a sentence if a phrase will do — describe the image, not the context surrounding it.

Don't start with "Image of" or "Photo of." Screen readers already announce "image" before reading alt text. Starting with "Image of..." is redundant and wastes the character budget on a word the user already heard.

What NOT to Do

Keyword stuffing. alt="link checker free online tool link checker best link checker seo" — this is a spam signal and provides no useful description of what the image shows. Google's quality guidelines call this out explicitly as a practice to avoid.

Copying the surrounding text. Alt text that duplicates the paragraph text creates repetition that screen readers read twice — once as body text and once when the image is encountered. Describe what's unique about the image, not what the caption already says.

Leaving it blank on informational images. An empty alt="" is correct for decorative images. But informational images — diagrams, screenshots, charts, product photos — must have descriptive alt text. Leaving these blank means the image contributes nothing to SEO and nothing to accessibility.

Using the filename. Many CMS platforms auto-populate alt text with the image filename. alt="IMG_2847" or alt="screenshot-2026-05-14" provides no value whatsoever. Always write a manual description — it takes 10 seconds and makes a genuine difference.

Decorative Images — Use Empty Alt

Decorative images that add no informational value should have an explicit empty alt attribute: alt="". Examples include dividers, abstract background patterns, icon decorations, spacers, and purely visual flourishes that have no content meaning.

With alt="", screen readers skip the image entirely — the correct behaviour for decoration. Without any alt attribute at all, some screen readers will read the filename instead, which is disruptive. There is an important distinction between omitting the attribute (bad for accessibility) and explicitly setting it to empty (correct for decorative images).

The WCAG 2.1 criterion for this is clear: all non-decorative images must have descriptive alt text; all decorative images must have alt="". Neither case allows a missing attribute.

Auditing Alt Text Across Your Site

Auditing manually is impractical for sites with 50+ pages. The SEO Analyzer crawls your entire site and flags every page with images missing alt text, reporting the count per page. Use the "images" filter tab to see all affected pages at once and prioritise which to fix first.

Common audit findings:

• Featured/hero images with no alt text — often the largest missed opportunity. These images appear in social shares and Google Image Search results, yet many sites leave their hero image alt attributes blank.
• Gallery images with alt="" when they're informational — product galleries, portfolio screenshots, and before/after comparisons are informational and should have descriptions, not empty alt text.
• Product images with only the SKU number — an alt like alt="SKU-48291" tells Google nothing about what the product looks like. Use the product name and a brief visual description.
• Blog post images auto-populated with filenames by the CMS — check your CMS default settings. WordPress, Webflow, and Squarespace all have different defaults, and many auto-populate from the filename unless configured otherwise.

Once you've identified the pages with missing alt text, prioritise by page importance: fix your highest-traffic pages and your most-linked product or service pages first. Even fixing the top 10 pages typically covers a significant proportion of your image SEO gap.

A Note on Long Descriptions

For complex images — data charts, detailed technical diagrams, maps — alt text alone may not be sufficient. In these cases, consider supplementing with a longdesc attribute pointing to a full text description, or simply include the same information as body text beneath the image. This serves both accessibility and SEO: the data in a chart becomes crawlable text rather than being locked inside pixels.

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