Image Alt Text Guide: Write Alt Text That Boosts SEO
Image alt text is one of the most consistently under-optimized elements on the web — most sites either leave it blank, use the filename, or write vague one-word descriptions that help neither users nor search engines. Done correctly, alt text strengthens your page's topical relevance, unlocks image search traffic, and satisfies WCAG accessibility requirements simultaneously. The guidance below covers everything from writing technique to auditing your existing library at scale.
What alt text does
Alt text (the alt attribute on img tags) serves two purposes: it describes images to screen readers for accessibility, and it tells Google what an image shows - since Google cannot see images the way humans do. Google uses alt text as a primary signal for image search rankings and as supporting keyword context for the surrounding page content. Every image on every indexed page should have descriptive alt text.
How to write good alt text
Describe what is actually in the image specifically and concisely. For a photo of a person using a laptop: woman using laptop to analyze website analytics data. For a product photo: Nike Air Max 90 running shoes in blue and white, side view. For an infographic: infographic showing 5 steps to fix a sitemap error. Bad alt text: image1.jpg, photo, logo. Good alt text uses the primary keyword of the page naturally when it accurately describes the image - not keyword-stuffed, just accurate.
Common alt text mistakes
Leaving alt text empty on non-decorative images: every meaningful image needs alt text. Using the filename as alt text (alt=IMG_4521): no keyword signal, no accessibility value. Keyword stuffing: alt=best SEO tools cheap SEO software buy SEO tool online - triggers spam signals. Same alt text on multiple images: Google needs unique descriptions. Decorative images (spacers, borders, purely visual elements) should have empty alt text (alt=) to signal they are intentionally empty, not forgotten.
Alt text for image search rankings
Google Images is a significant traffic source for product, recipe, travel, and how-to content — often overlooked by SEOs focused on web search. Alt text is the primary on-page signal Google uses to decide what queries an image should rank for. For product images, include the product name, model, color, and a brief descriptor. For editorial images, describe what is happening and why it is relevant to the surrounding content. Optimized alt text on high-quality images can drive thousands of additional monthly visits from image search alone.
Image file names reinforce alt text signals
The image filename is another crawlable signal Google uses before it even reads the alt attribute. Rename images from their camera defaults (DSC00421.jpg) to descriptive slugs before uploading: sitemap-error-in-google-search-console.jpg. Use lowercase letters, hyphens as separators, and include your primary keyword where it accurately describes the image. Consistent descriptive filenames across your entire media library compound over time, particularly for image search visibility.
Context and surrounding text matter
Google does not evaluate alt text in isolation — it considers the entire page context when interpreting an image. An alt text of 'bar chart' on a page about organic traffic growth will be understood differently than the same alt text on a finance page. Make alt text as specific as possible, but know that a well-written surrounding paragraph reinforces and clarifies ambiguous alt text. For complex charts or graphs, supplement alt text with a text-based description of the key data points directly in the page copy.
Audit your alt text coverage at scale
Most sites have hundreds of images with missing or inadequate alt text accumulated over years of content publishing. Run a site crawl using Screaming Frog (free up to 500 URLs), Sitebulb, or a similar tool and export the Images report. Filter for empty alt attributes, generic filenames used as alt text, and alt text that is identical across multiple images. Prioritize fixing images on your top-traffic pages first — the pages with the most impressions and traffic benefit most from immediate alt text improvements.
Next.js Image component and alt text
In Next.js, the Image component requires an alt prop — the compiler throws an error if you omit it. This is a good safety net, but it does not prevent developers from setting alt='' on non-decorative images or using placeholder strings like alt='image'. Review all Image component usage in your codebase and confirm each alt prop contains an accurate, keyword-relevant description. For dynamically loaded images (from a CMS or API), ensure the content model includes an alt text field that editors are required to populate before publishing.