# ComboStrap Page Metadata - Canonical URL

A canonical URL is an identifier for a web page that is defined through the canonical meta property.

It identifies uniquely a page in a domain.

The canonical value:

• should never change (theoretically)
• does not need to be the pagename
• is always lowercase

The canonical component is a part of the SEO module.

## How to set the canonical value ?

### Manually

To set the canonical value, uses the frontmatter component and add the canonical property in the JSON document.

---json
{
"canonical":"my:canonical:id"
}
---


### Automatically

This plugin can create a canonical value based on the last parts of a page ID. See ComboStrap Page Metadata - Automatic Canonical

By setting a canonical value, you will get two head properties in your HTML page.

For instance:

• if the canonical value is cat:post1
• on a page hosted at example.com

the canonical head properties would become

<link rel="canonical" href="https://example.com/cat/post1" />

<meta property="og:url" content="https://example.com/cat/post1" />


## Demo

This page has the canonical value set to canonical:url and therefore is also available at this Canonical URL.

In dokuwiki, a red hyperlink means that the file does not exist but with the canonical feature, the page exists.

or

## Usage

All external provider will use this value to refer to your page.

For instance:

## For the Geek

The canonical is explained in depth in the RFC6956 - the Canonical Link Relation