Impact of robots.txt on crawling of CSS, JavaScript, and other resources

Blocking CSS, JavaScript, and other resources via robots.txt negatively impacts how search engines crawl, render, and index your website. When these resources are disallowed, Googlebot cannot fully understand how your pages appear and function, which can harm your site's ranking and indexing quality. This is because Google uses CSS and JS to render pages similarly to how users see them, and blocking these files essentially "blinds" the crawler to the true page experience.

Specifically:

• Blocking CSS and JS files prevents Google from rendering the page properly, leading to poorer indexing and potentially lower rankings.
• Google explicitly advises against disallowing crawling of CSS and JavaScript in robots.txt because it directly harms how their algorithms render and index content.
• There is no need to explicitly allow CSS and JS in robots.txt; simply avoid disallowing their directories or files.
• If CSS or JS files are blocked, Google may not see important page elements such as product reviews or interactive features, which can reduce SEO effectiveness.
• Tools like SEO spiders will flag URLs blocked by robots.txt as critical issues if those URLs are important for indexing.

In summary, robots.txt should not block CSS, JavaScript, or other essential resources to ensure proper crawling, rendering, and indexing by search engines. Only block resources if absolutely necessary for server performance or security, and even then, consider the SEO trade-offs carefully.