seo/canonical-url · Canonical URL

Every route should include a <link rel="canonical"> tag.

Severity: warning

What it checks

Every route should include a <link rel="canonical"> tag (own or inherited through the layout chain). A missing or empty canonical link is flagged.

On a route that sends visitors without a session away, the finding is reported as info instead: a crawler has no session, so it only ever sees the redirect or error. Source analysis recognizes a server load, the page’s own or a layout’s above it, that starts with a check on the request’s locals alone, such as if (!locals.user) redirect(…) or error(401). A gate in hooks.server.ts or in the browser is not read, so routes guarded that way keep warning; turn the rule off for them with overrides, or set seo: { indexable: false } for a whole private app. A severity set for the rule in rules applies on these routes too.

Why it matters

A canonical URL tells search engines which URL is authoritative, preventing duplicate-content dilution across query-string variants of the same page. (SvelteKit normalizes trailing slashes itself by default, so that particular variant isn’t a concern here.)

How to fix

Add <link rel="canonical"> in <svelte:head>, or set the canonical prop on your meta component:

<svelte:head>
  <link rel="canonical" href="https://example.com/this-page" />
</svelte:head>

Mode differences

Source analysis (the CLI, the dashboard’s static baseline) composes each route’s <head> from <svelte:head> in the page and its layout chain, followed into repo-local components, plus the known meta components (svelte-meta-tags, svelte-seo, svead) and any you declare in metaComponents. A value it cannot read literally ({data.title}) is dynamic, judged by treatDynamicAs. A component a function mounts with import() renders only in the browser: its <link rel="canonical"> counts on a route with ssr = false, and not on a server-rendered route, whose HTML has none. Rendered analysis (the Vite plugin’s build pass, a route you visit in the dashboard) reads the shipped <head>, where every value is literal and treatDynamicAs does not apply; the build pass covers prerendered routes only. When the two disagree, trust the rendered result.

Disabling

Record existing findings in the suppressions file (npx svelte-vitals --update-suppressions), scope the rule per route or path with overrides, or turn it off:

export default {
  rules: {
    'seo/canonical-url': 'off'
  }
};