---
title: "Canonical URL (rel=\"canonical\")"
category: foundations
status: recommended
url: https://specification.website/spec/foundations/canonical-url/
updated: "2026-05-29"
sources:
- title: "RFC 6596 — The Canonical Link Relation"
url: "https://www.rfc-editor.org/rfc/rfc6596"
publisher: "IETF"
- title: "MDN — rel=canonical"
url: "https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel/canonical"
publisher: "MDN"
- title: "Google — Consolidate duplicate URLs with canonicals"
url: "https://developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls"
publisher: "Google Search Central"
- title: "HTML Living Standard — Link types: canonical"
url: "https://html.spec.whatwg.org/multipage/links.html#link-type-canonical"
publisher: "WHATWG"
source_repo: https://github.com/jdevalk/specification.website
licence: CC-BY-4.0
---
# Canonical URL (rel="canonical")
> Declare the preferred URL for a page so search engines and crawlers consolidate ranking signals on one address, even when several URLs serve the same content.
## What it is
The canonical link tells crawlers which URL is the authoritative version of a page when the same content is reachable through several addresses:
```html
```
It belongs in `` and was standardised in [RFC 6596](https://www.rfc-editor.org/rfc/rfc6596). All major search engines honour it.
## Why it matters
The same content often lives at multiple URLs without anyone meaning it to:
- `https://example.com/page` and `https://www.example.com/page`
- `http://` and `https://` versions of the same path
- `/page` and `/page/` (with and without trailing slash)
- `/page?utm_source=newsletter` and `/page` (tracking parameters)
- `/page?sort=date` and `/page?sort=name` (filter and sort variants)
- Paginated archives, printer-friendly views, AMP versions
Without a canonical, crawlers may index every variant separately, splitting ranking signals and backlinks across duplicates. With a canonical, those signals consolidate on one URL. The result is a stronger ranking for the page you actually want to rank, and a cleaner index.
A canonical is a **strong hint**, not an absolute directive. Search engines can override it if other signals (sitemaps, redirects, internal links) point elsewhere. Make all your signals agree.
## How to implement
Put a **self-referencing canonical** on every public HTML page. Even pages without duplicates benefit: it removes ambiguity for query-string variants and short-circuits any scraper that copies the page.
```html
```
Rules:
- **Use absolute URLs.** Include the scheme (`https://`) and host. Relative canonicals are allowed by the spec but more error-prone; absolute is the safer default.
- **Match the scheme you actually serve.** If the site is HTTPS everywhere, canonicals must say `https://`.
- **Pick one host and stick to it.** Either `example.com` or `www.example.com`, never both. Redirect the other.
- **Be consistent about trailing slashes.** If `/articles/` and `/articles` resolve to the same content, pick one and canonicalise to it. Mixed is the worst case.
- **Strip tracking parameters** from the canonical. The canonical of `/page?utm_source=newsletter` is `/page`.
- **Avoid loops.** Page A canonical to B, B canonical to A is a contradiction.
- **One per page.** Multiple canonicals are ignored.
Cross-domain canonicals are valid when content is syndicated. If you republish an article on a partner site, the partner can canonical back to your original:
```html
```
For pages that exist in multiple languages, use `hreflang` in addition to `canonical`. Each language version is its own canonical; `hreflang` ties them together.
The canonical can also be sent as an HTTP header, which is useful for non-HTML resources like PDFs:
```http
Link: ; rel="canonical"
```
## Common mistakes
- Pointing every page's canonical at the homepage. This tells crawlers your inner pages are duplicates of the homepage and de-indexes them.
- Canonicalising paginated archives (`?page=2`) to page 1. Each pagination page is distinct content; let them index normally.
- Setting a canonical on `https://` that points to `http://`, or vice versa.
- Forgetting to update the canonical when the site moves domain.
- Generating canonicals from `window.location` in client-side JS only. Crawlers may not run JS; render server-side.
## Verification
- View source on a few pages with query parameters. The canonical should ignore the parameters and point to the clean URL.
- Run `document.querySelector('link[rel=canonical]').href` in DevTools.
- Crawl the site and list canonical targets. Every target should return 200 OK, not a redirect.
- In Google Search Console, the "URL Inspection" tool shows the user-declared canonical and the Google-selected canonical. When they differ, something else is overriding your hint.