---
title: "Canonical URL (rel=\"canonical\")"
category: foundations
status: recommended
url: https://webspecification.com/spec/foundations/canonical-url/
updated: "2026-07-09T00:00:00.000Z"
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/Reference/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: undefined
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.
A canonical is not a redirect, and it is not `noindex`. The other URLs stay live, keep returning `200`, and stay crawlable; nothing changes for a visitor who lands on one. The tag only asks search engines to _attribute_ the content to the URL you name, so ranking signals, backlinks, and the indexed address consolidate there instead of splitting across the duplicates. It changes where credit lands, not what is reachable.
## 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. Consolidating them gives 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.