A canonical URL tells search engines which version of a blog post is the original one. It prevents duplicate content, keeps your site organized, and makes sure Google ranks the right page. By setting a canonical tag, you guide search engines to your preferred URL so your blog keeps its SEO strength in one place.

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What Is a Canonical URL?

A canonical URL is the “preferred” version of a webpage that you want search engines to index. It tells search engines:
“This is the official version of this page. ”This is important when you have duplicate or similar content across multiple URLs.

You have several URLs showing the same product:

/shirt?color=blue
/shirt?size=medium
shirt/blue

A canonical tag points to the URL you want Google to count as the main page:

What Is a URL?

A URL (Uniform Resource Locator) is the address of a webpage. It’s what you type into a browser to visit a website. It’s one of the basic building blocks of on-page SEO. It plays a big role in user experience and how search engines understand your website.

Example:

A URL tells both users and search engines where a page lives on your site

Parts of a URL

Protocol – https://
Shows the connection type. HTTPS is secure and preferred by Google.
Domain Name – example.com
The main address of the website.
Subdomain (optional) – www.
A section of your website, such as blog.example.com.
Path – /blog/how-to-do-SEO
The location of a specific page.
Parameters (optional) – ?id=123
Often used for tracking or dynamic pages. Best to avoid SEO unless necessary.

Canonical URL vs 301 Redirect

Feature	Canonical URL	301 Redirect
Purpose	Tells Google which version of similar pages is the preferred one	Permanently moves users and search engines to a new URL
User Redirect?	❌ No	✅ Yes
Page Removed?	❌ No, all versions stay live	✅ Yes, old page becomes inactive
Google Signal Strength	Medium (a hint)	Strong (a directive)
Best For	Duplicate pages that must stay online	Pages you want to delete, replace, or merge
SEO Value Transfer	Partial / depends on Google	Full SEO value passed to the new URL
Use Case in Blogs	Tag pages, UTM links, similar versions	Merging old posts into a new updated post
Use Case in E-commerce	Filters (size, color), sorting URLs	Discontinued products, outdated URLs
Keeps Multiple URLs Active?	✔ Yes	❌ No
Prevents Duplicate Content?	✔ Yes	✔ Yes
Affects Site Navigation?	❌ No	✔ Yes
Technical Complexity	Easy to set	Moderate (requires server or CMS settings)
Example	Keep /shirt?color=blue, but tell Google /shirt is main	Redirect /old-blog-post → /new-blog-post

Fixing Duplicate Content With Canonicalization

If you have 4 different URLs showing the same content, Google sees them as duplicate pages. This can hurt your SEO because:

Google doesn’t know which URL to index
Ranking power gets split between the duplicate URLs
Crawl budget gets wasted

The best solution is canonicalization — choosing one URL as the “main” page.

For example:

Imagine you have a product page for a pair of sports shoes.

4 Alternate URLs:

https://example.com/product/sport-shoes
https://example.com/product/sport-shoes?color=red
https://example.com/product/sport-shoes?ref=homepage
https://example.com/product/sport-shoes?size=9

If https://example.com/product/sport-shoes is the main product page, the canonical tag <link rel=”canonical” href=”https://example.com/product/sport-shoes”> should be added to all duplicate pages to indicate that this is the preferred version for indexing.

Result

All duplicate URLs point to a single preferred page.
Google treats the canonical URL as the primary page for ranking.
All ranking signals (links, authority, etc.) are consolidated into the canonical page.

This is exactly how canonicalization works. Why it’s good for SEO: It prevents duplicate content issues and ensures your main page gets the full SEO benefit.

What is a self-referencing canonical?

A self-referencing canonical is when a page points to itself in its canonical tag. For example:

Here, the page sport-shoes is telling search engines: “This is the preferred version of this content,” even if it doesn’t have duplicates yet.

How to Optimize Canonical URLs in SEO

Add a canonical tag to every page
Point canonicals to the main version of the page
Avoid self-canonical errors
Use 301 redirects when necessary
Keep consistent internal links

What This Canonical Tag Does

1. Prevents duplicate content: If Google finds duplicates or tracking parameters, it will still choose this page.
2. Combines ranking signals: Backlinks, engagement, and metrics from other versions will be credited to this URL.
3. Sends a strong signal: “It’s this page—not any variation—that should rank.”
4. Protects your SEO: Avoids split ranking and confusion for Google’s crawlers.