# aFarkas/lazysizes

High performance and SEO friendly lazy loader for images (responsive and normal), iframes and more, that detects any visibility changes triggered through user interaction, CSS or JavaScript without configuration.

Repository: https://github.com/aFarkas/lazysizes
Canonical: https://ross.abutalabs.com/products/lazysizes
Language: JavaScript
License: MIT
License Family: permissive
Topics: javascript, lazyload, lazy-evaluation, lazysizes, responsive-images, performance
Last push: 2024-04-03T08:17:04+00:00

## Health v2 (maintenance only)
Score: 23/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 8, longevity 100
- inputs: {"age_days": 4344, "days_push": 882, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 17718, forks 1690 (observed 2026-08-28T04:11:20.221444+00:00)

## What it is
lazysizes is a high-performance, SEO-friendly lazy loader for images (including responsive picture/srcset), iframes, scripts, and widgets. It self-initializes without configuration, detects visibility changes from user interaction, CSS, or JavaScript, and can automatically calculate the sizes attribute for responsive images.

## Use cases
- lazy load images on a webpage to improve page speed
- defer loading of YouTube or Vimeo iframes until scrolled into view
- implement responsive images with automatic sizes calculation
- lazy load widgets and scripts embedded in a page
- improve perceived performance by prioritizing in-view and near-view resources
- add lazy loading to a site without writing JavaScript configuration

## When to choose
- you need a zero-configuration, drop-in lazy loader for images and iframes
- you want SEO-friendly lazy loading that works without JavaScript setup
- you need automatic sizes attribute calculation for responsive images
- you want jank-free scrolling performance while lazy loading

## When to avoid
- you only target modern browsers and prefer native loading="lazy" attributes
- you need lazy loading for non-DOM content like data or modules
- your project requires a framework-integrated lazy loading solution with React/Vue components

## Facets
- artifact type: library
- maturity: maintenance
- function: image-processing, developer-tools
- domain: web-development, frontend, performance
- platform: browser
- tags: lazy-loading, responsive-images, seo, srcset, intersection-observer, vanilla-js, nodejs

## Member repositories
- aFarkas/lazysizes (main) score 23

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:11:20.221444+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T17:02:28.888191+00:00, confidence not recorded.
  - readme: https://github.com/aFarkas/lazysizes (fetched 2026-08-28T04:11:20.221444+00:00, sha 37db9fe3fb49)
  - registry_npm: https://registry.npmjs.org/lazysizes (fetched 2026-08-29T08:00:57.396989+00:00, sha 42c7b6b4dc73)
- Data as of 2026-08-30T08:39:29.467469+00:00.