What image file size thresholds does this skill check?

It applies tiered thresholds by image category: thumbnails under 50KB, content images under 100KB, and hero/banner images under 200KB, with warning and critical tiers above those limits.

Does this skill check lazy loading, and what mistakes does it catch?

Yes, it verifies that `loading="lazy"` is applied only to below-fold images and critically flags when it's incorrectly applied to above-fold or LCP images, which harms LCP scores.

What image formats does this skill recommend, and why?

It recommends WebP (97%+ browser support) or AVIF (92%+, best compression) over JPEG/PNG via a progressive-enhancement ` ` element pattern with format fallbacks, and notes JPEG XL as an emerging format not yet practical for deployment.

What does the skill output after analyzing a URL?

It produces an Image Audit Summary table (total images, missing alt text, oversized, wrong format counts), a prioritized optimization list ranked by estimated file-size savings, and numbered recommendations for format conversion, alt text, dimensions, lazy loading, and compression.

What happens if images are behind a CDN or authentication?

The skill reports available markup metadata like alt text, dimensions, and format, but flags what could not be directly accessed for size analysis.

Skill

Analyze and Optimize Website Images for SEO

Name: Image Optimization Analysis
Availability: OnlineOnly
Author: Antigravity

A skill that audits image SEO and Core Web Vitals signals - alt text, file size, format, lazy loading, and CLS prevention.

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Spark score

out of 100

Updated last month

Version 13.1.1

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Why it matters

Automate the analysis of website images to ensure optimal SEO performance, file size, format, and loading speed. This asset provides actionable recommendations to improve Core Web Vitals and search engine rankings.

Outcomes

What it gets done

Audit image alt text for presence, descriptiveness, and keyword usage.

Analyze image file sizes against tiered thresholds and recommend compression.

Evaluate image formats for browser support and recommend optimal choices (WebP, AVIF).

Check for proper implementation of responsive images, lazy loading, and CLS prevention attributes.

Install

Add it to your toolbox

Run in your project directory:

curl -fsSL https://spark.entire.vc/get/ag-seo-images | bash

Overview

Image Optimization Analysis

A skill that audits image SEO and Core Web Vitals signals - alt text, file size, format, lazy loading, fetchpriority, and CLS-preventing dimensions - with a prioritized optimization list. Use it for a focused image-only SEO/performance audit, not as a full-site technical SEO audit.

What it does

This skill audits image-specific SEO and performance signals that affect both search visibility and Core Web Vitals. It checks alt text presence, descriptiveness (not a filename or "click here"), keyword naturalness, and length (10-125 characters), with worked good/bad examples. It applies tiered file-size thresholds by image category (thumbnails under 50KB, content images under 100KB, hero/banner images under 200KB, with warning and critical tiers above those) and recommends format modernization - WebP (97%+ browser support) or AVIF (92%+, best compression) over JPEG/PNG - via a progressive-enhancement <picture> element pattern with format fallbacks, and notes JPEG XL as an emerging format Chrome is restoring support for (not yet practical for deployment). It checks responsive image markup (srcset/sizes matching layout breakpoints), lazy-loading correctness (loading="lazy" on below-fold images only - critically, never on above-fold/LCP images, which harms LCP scores), fetchpriority="high" on the LCP image, decoding="async" on non-LCP images to avoid blocking the main thread, and CLS prevention via explicit width/height attributes or CSS aspect-ratio. It also checks SEO-friendly file naming (descriptive, hyphenated, lowercase) and CDN usage for image delivery. Output is an Image Audit Summary (total images, missing alt text, oversized, wrong format, no dimensions, not lazy-loaded counts), a prioritized optimization list sorted by estimated file-size savings, and numbered recommendations (format conversion, alt text additions, dimension additions, lazy-loading enablement, compression targets).

When to use - and when NOT to

Use it when auditing image SEO, alt text, file sizes, formats, or lazy loading specifically, or when checking media quality signals affecting both SEO and Core Web Vitals. On an unreachable URL it reports the connection error and status code; if no `` elements are found it suggests checking for JavaScript- or CSS-background-image-loaded images rather than assuming there are none; for images behind a CDN or authentication it reports available markup metadata (alt text, dimensions, format) and flags what could not be directly accessed for size analysis.

Inputs and outputs

Inputs: a target URL to analyze for image markup and (where accessible) file sizes.
Outputs: an Image Audit Summary table, a prioritized optimization list ranked by estimated savings, and specific numbered recommendations for format conversion, alt text, dimensions, lazy loading, and compression.

<picture>
  <source srcset="image.avif" type="image/avif">
  <source srcset="image.webp" type="image/webp">
  
</picture>

Who it's for

SEO and web performance teams who need a focused image-only audit covering alt text, file size, format, and Core Web Vitals-affecting attributes (lazy loading, fetchpriority, dimensions) rather than a full-site technical audit.

FAQ

Common questions

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