Glossary · HTTP, edge and rendering
lazy loading
Deferring an image or frame until it is about to enter the viewport, by the loading=lazy attribute or by script.
What lazy loading means
Deferring an image or frame until it is about to enter the viewport, by the loading=lazy attribute or by script. It saves bandwidth below the fold and costs paint time above it: an image the page opens with that is marked lazy arrives later than it would have unmarked, and a script-only lazy loader shows a crawler nothing at all.
What lazy loading can and cannot support
| It can support | It cannot support |
|---|---|
| Deferring an image or frame until it is about to enter the viewport, by the loading=lazy attribute or by script. | It saves bandwidth below the fold and costs paint time above it: an image the page opens with that is marked lazy arrives later than it would have unmarked, and a script-only lazy loader shows a crawler nothing at all. |
Where lazy loading comes up on this site
- Our scanner counted 14 placeholders and none of the 13 photographsThe modern-format and data-URI figures are reported, not scored: the scored image rows are a missing alt attribute, width and height on at least nine images in ten, no lazy loading above the fold, and an image declared in the page schema and in the Open…
Related terms in HTTP, edge and rendering
The delivery layer between an origin and a client: proxies, caches, redirects, status codes and the headers that decide what a crawler actually received.
Origin server · Reverse proxy · CDN · Edge node · WAF · Bot score · TLS handshake · DNS resolution · DNS timeout · Connection timeout · Read timeout · Redirect chain · Redirect loop · 301 redirect · 302 redirect · 307 redirect · 308 redirect · 304 response · 404 response · 410 response · 429 response · 500 response · 502 response · 503 response · 504 response · HEAD request · GET request · Content type · MIME sniffing · Content encoding · Compression · Brotli · ETag · Last-Modified · If-None-Match · Cache hit · Cache miss · Cache key · Vary header · Stale response · Stale-while-revalidate · Edge redirect · Origin bypass · Response parity · Header parity · hreflang · canonical URL · HSTS · HSTS preload list · Content-Security-Policy · CSP nonce · edge cache · cache split · cache-buster · Cache-Control · Age header · render-blocking resource · payload text share · 404 and 410 status codes
Questions about lazy loading
What is lazy loading?
Deferring an image or frame until it is about to enter the viewport, by the loading=lazy attribute or by script.
What does lazy loading not show or guarantee?
It saves bandwidth below the fold and costs paint time above it: an image the page opens with that is marked lazy arrives later than it would have unmarked, and a script-only lazy loader shows a crawler nothing at all.
Which area of the glossary does lazy loading belong to?
HTTP, edge and rendering: The delivery layer between an origin and a client: proxies, caches, redirects, status codes and the headers that decide what a crawler actually received.
← payload text share · 404 and 410 status codes →
See it in the full glossary · 668 terms across 19 areas.