AltText.AI

Image SEO analyzer

Check the parts of an image that search engines and page speed care about: file name, format, pixel size and weight. The analysis runs in your browser.

Drop images to analyze

Up to 20 at a time · nothing is uploaded for the analysis ·

Image SEO checklist

  1. Use a real <img> element. Google says it does not index CSS background images as images.
  2. Write alt text that describes the image in context. It is the strongest text signal attached to the image itself, and it is an accessibility requirement. Generate a draft with the alt text generator.
  3. Name the file descriptively: sage-green-ceramic-teapot.webp, not IMG_4031.jpg. Lowercase, hyphens.
  4. Place it near relevant text. Headings, captions and nearby paragraphs help Google understand the image.
  5. Serve the right size. Use srcset/sizes so phones do not download desktop pixels.
  6. Use modern formats. WebP or AVIF with a JPEG fallback if you must support very old browsers.
  7. Set width and height to avoid layout shift (CLS), and loading="lazy" on below-the-fold images, but never on the main hero, which hurts LCP.
  8. Add images to your sitemap or use structured data (e.g. Product, Recipe) where it applies.

Sources: Google Search Central, Image SEO best practices; web.dev, Optimize Largest Contentful Paint.

Responsive image snippet

<img
  src="teapot-800.webp"
  srcset="teapot-480.webp 480w,
          teapot-800.webp 800w,
          teapot-1600.webp 1600w"
  sizes="(min-width: 900px) 50vw, 100vw"
  width="1600" height="1195"
  alt="Sage-green ceramic teapot
       with a bamboo handle"
  loading="lazy">

The browser picks the smallest file that fills the slot at the screen's pixel density.

Questions people ask

What makes an image SEO-friendly?

Google's image SEO guidelines point to a descriptive file name, useful alt text, relevant surrounding text, a responsive image in a standard <img> element, and a file small enough to load fast. Format and dimensions also affect Largest Contentful Paint, a Core Web Vital.

Does the image file name matter for SEO?

Google says file names can give it light clues about the subject, so "sage-green-ceramic-teapot.jpg" is better than "IMG_4031.jpg". It is a small signal; alt text and page context matter more.

What is a good file size for web images?

There is no official number. As a working rule, keep large hero images under about 200 KB and in-content images under about 100 KB, and never ship pixels far beyond the largest size the image is displayed at (roughly 2× for high-density screens).

Should I use WebP or AVIF?

Both are supported by all current major browsers and are usually much smaller than JPEG or PNG at similar quality. WebP encodes faster and is supported everywhere; AVIF is often smaller still. This analyzer estimates WebP savings because browsers can encode it on the spot.

Are my images uploaded?

Not for the analysis. File name, format, dimensions and the WebP estimate are all computed in your browser. Only if you press "Suggest alt and file name" is a resized copy sent to the AI model for that one request, and it is not stored.