--- title: "JavaScript changes canonical, robots, title or description after load (seo/head-js-mutation)" description: "seo/head-js-mutation: Google may skip rendering when raw HTML says noindex, and it compares raw vs rendered canonicals; non-rendering AI crawlers only ever…" canonical: https://void-design.vercel.app/rules/seo/head-js-mutation lastModified: 2026-09-16 --- # JavaScript changes canonical, robots, title or description after load `seo/head-js-mutation` · severity **error** · category SEO · detected by `void seo` and `void audit` ## 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 - https://developers.google.com/search/docs/crawling-indexing/javascript/javascript-seo-basics ## 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 , self-referencing canonicals, one h1, crawlable links, Open Graph, icons, robots.txt and a sitemap with real dates. - `canonical-invalid` Canonical URL is relative or contains a fragment — [seo/canonical-invalid](https://void-design.vercel.app/rules/seo/canonical-invalid) - `canonical-broken` Canonical points to a URL that returns 4xx/5xx — [seo/canonical-broken](https://void-design.vercel.app/rules/seo/canonical-broken) - `canonical-conflict` Canonical target redirects, is noindex, or canonicalises elsewhere — [seo/canonical-conflict](https://void-design.vercel.app/rules/seo/canonical-conflict) - `canonical-not-self` Canonical points to a different URL — [seo/canonical-not-self](https://void-design.vercel.app/rules/seo/canonical-not-self) - `h1-count` Page doesn't have exactly one visible

in the server HTML — [seo/h1-count](https://void-design.vercel.app/rules/seo/h1-count) - `h1-title-mismatch`

and share little wording — [seo/h1-title-mismatch](https://void-design.vercel.app/rules/seo/h1-title-mismatch) - `heading-skip` Heading levels skip (h2 → h4) or headings are empty — [seo/heading-skip](https://void-design.vercel.app/rules/seo/heading-skip) - `img-alt-missing` <img> without an alt attribute — [seo/img-alt-missing](https://void-design.vercel.app/rules/seo/img-alt-missing) Detected by `void seo` and `void audit`. Explain it in a terminal: `void rules seo/head-js-mutation`