SEO Considerations

Search engine bots and crawlers don't behave like human visitors: Googlebot supports native loading="lazy" but does not scroll the page, and most social scrapers (Slackbot, Twitterbot, facebookexternalhit) don't run JavaScript at all. For crawlers that do, unlazy detects them and loads the full-quality image immediately, so the blurry placeholder isn't what gets indexed.

Crawlers Get the Real Image

unlazy exports an isCrawler constant that is true when the current visitor is detected as a bot or crawler. For a crawler, data-src and data-srcset become src and srcset immediately, so the full-quality image is what gets indexed.

Use the sizes attribute (or data-sizes="auto" for automatic calculation) to provide search engines with the intended display size.