Why it matters
Google may skip rendering when raw HTML says noindex, and it compares raw vs rendered canonicals; non-rendering AI crawlers only ever see the raw values. Changed canonical/robots is an error, changed title/description a warning.
How to fix it
Render head metadata on the server (metadata/generateMetadata) and don't set document.title or canonical links from client effects.
References
More seo rules
void seo reports 60 rules in this category. What search engines need from the raw response: status codes, titles and descriptions in <head>, self-referencing canonicals, one h1, crawlable links, Open Graph, icons, robots.txt and a sitemap with real dates.
canonical-invalidCanonical URL is relative or contains a fragmentcanonical-brokenCanonical points to a URL that returns 4xx/5xxcanonical-conflictCanonical target redirects, is noindex, or canonicalises elsewherecanonical-not-selfCanonical points to a different URLh1-countPage doesn't have exactly one visible <h1> in the server HTMLh1-title-mismatch<h1> and <title> share little wordingheading-skipHeading levels skip (h2 → h4) or headings are emptyimg-alt-missing<img> without an alt attribute