What is a canonical tag and why does it matter for SEO?

A canonical tag is an HTML link element placed in the head of a page that tells Google which URL is the preferred version of that page. It looks like: rel=canonical href=https://example.com/page. Without it, Google may index multiple versions of the same content (with and without www, with different query strings, etc.) and split your ranking signals across all of them. A correct canonical tag consolidates all ranking power to one preferred URL.

What happens when a page has no canonical tag?

When a page has no canonical tag, Google tries to determine the canonical URL itself using other signals. This means Google may choose a different URL than you want as the preferred version. For example, it might choose the HTTP version instead of HTTPS, or the www version instead of non-www. Always adding a self-referencing canonical tag removes this ambiguity and gives Google a clear signal about which URL to index and rank.

Can a page have both a canonical tag and a noindex tag?

Having both canonical and noindex on the same page sends conflicting signals to Google. Canonical says index this preferred version while noindex says do not index this page at all. Google typically follows the noindex instruction, but the conflict weakens both signals. Best practice is to use canonical only on indexable pages and noindex only on pages you genuinely want excluded from the index.

Should I use absolute or relative URLs in canonical tags?

Always use absolute URLs in canonical tags. A relative URL like /page can be interpreted differently depending on the context, especially on CDNs or if content is syndicated. An absolute canonical like https://example.com/page is unambiguous and works correctly in every situation. Google specifically recommends absolute URLs for canonical tags to avoid any misinterpretation.

Single URL Check · Full Website Crawl · Duplicate Detection

Canonical Tag
Checker Free

Q: What is a duplicate canonical issue?

A duplicate canonical issue occurs when multiple pages on your site all point their canonical tag to the same single URL. For example, if page A, page B, and page C all have rel=canonical pointing to page A, then Google understands pages B and C are duplicates of A. This is sometimes intentional for paginated content or syndication, but if it happens accidentally it tells Google to ignore entire pages of your site.

Instantly check canonical tags on any single URL, or crawl your entire website to find missing canonicals, duplicate canonical issues, HTTP vs HTTPS conflicts, relative URLs, noindex conflicts, and pages where multiple URLs share the same canonical. Free, no login.

Single URL canonical check

Full website crawl up to 50 pages

Duplicate and missing detection

HTTP, relative, fragment checks

🔍

Deep Single Check

7 canonical checks per URL

🌐

Website Crawl Mode

Up to 50 pages at once

🔁

Duplicate Groups

Pages sharing same canonical

⚡

Filterable Results

Filter by issue type instantly

Check Canonical Tags Free

Check a single page in detail, or crawl your whole website to find every canonical issue at once.

Page URL to Check

The Analysis Process

How the Free Canonical Tag Checker Works

Every check runs server-side on live page HTML so you see exactly what Google sees, not what your browser renders.

Fetch Live HTML

The tool fetches the page HTML exactly as Google's crawler would, following redirects and reading the raw server response, not the JavaScript-rendered DOM.

Extract Canonicals

All canonical link tags are extracted from the HTML head. The tool detects both standard and reversed attribute order to catch any valid format of the canonical tag.

Count and Validate

The number of canonical tags is checked. Missing, single, and multiple canonicals each trigger different issue levels. Single canonicals are then checked for 6 quality issues.

Cross-Reference

In website crawl mode, the crawler follows internal links and builds a map of all canonical URLs found. Pages that share the same canonical are flagged as a duplicate group.

Score and Report

A score (0 to 100) and grade are calculated for each page. The crawl mode produces a filterable table sorted by severity so you can fix the worst issues first.

Complete Guide

Canonical Tags for SEO: Everything You Need to Know

How to implement, validate, and fix canonical tag issues using our free canonical tag checker.

🔗

What Is a Canonical Tag and Why Does Every Page Need One?

A canonical tag is an HTML element placed in the head of your page that looks like <link rel="canonical" href="https://example.com/page" />. It tells Google which URL is the single preferred version of that page that should be indexed and ranked.

Without a canonical tag, Google encounters the same or very similar content at multiple URLs (with www and without, with HTTP and HTTPS, with trailing slashes and without, with query parameters added by analytics or ads) and must decide on its own which version to index. Google often guesses wrong. A canonical tag removes all ambiguity and consolidates all ranking signals to the one URL you actually want to rank.

The Self-Referencing Canonical Rule

Every indexable page should have a canonical tag pointing to itself, even if you think there is only one version of the URL. This is called a self-referencing canonical and it is the default correct state. It prevents parameter-appended versions of your URL (like ?utm_source=email) from being treated as separate pages by Google.

🚨

The 6 Most Common Canonical Tag Issues

Our free canonical checker audits every page for these six specific problems that affect how Google indexes your site.

1. Missing Canonical Tag

The most common issue. No canonical means Google decides the preferred URL itself, which often results in the wrong version being indexed.

2. Multiple Canonical Tags

When two or more rel="canonical" tags appear on the same page, Google ignores all of them. This is worse than having none because it actively breaks canonical consolidation.

3. HTTP Canonical on HTTPS Page

A canonical pointing to the HTTP version of a page when the page is served over HTTPS creates a conflicting signal. Always match the protocol of your canonical to the live protocol.

4. Relative URL in Canonical

Using /page instead of https://example.com/page in the canonical can cause misinterpretation. Always use absolute URLs.

5. Canonical with Fragment

The fragment part of a URL (the #section part) is ignored by Google. A canonical containing a fragment is treated as pointing to the URL without the fragment.

6. Canonical and Noindex Conflict

Having both a canonical and a noindex tag on the same page sends contradictory signals. Google typically follows noindex, making the canonical irrelevant.

🌐

What Is a Duplicate Canonical Issue Across a Website?

A duplicate canonical issue occurs when multiple different pages all point their canonical tag to the same single URL. For example, if your blog has 20 archive pages and all 20 declare rel="canonical" pointing to the main blog page, you are telling Google that all 20 archive pages are duplicates of the main blog page and should not be indexed.

This is sometimes intentional, for example on paginated archive pages you might canonicalise everything to page 1. But it is frequently accidental, for example when a CMS template uses a hardcoded canonical URL instead of a dynamic one. Our free website crawl mode specifically detects these groups of pages sharing a canonical and reports them as a critical issue.

How to Fix Duplicate Canonicals

Each unique page should have its own self-referencing canonical. Check your CMS theme files and SEO plugin settings to ensure canonical tags are generated dynamically based on the current page URL, not hardcoded to a single value. In WordPress, check that your SEO plugin (Yoast, Rank Math, etc.) is set to output canonical tags automatically for every page type.

🕸

How to Use the Website Crawl Mode

The website crawl mode is the most powerful feature of this free canonical checker. Enter your homepage URL, select how many pages to crawl (up to 50), and click Check. The tool crawls your site starting from the homepage, follows every internal link it finds, and checks the canonical tag on each page.

The crawl results show a full table of every page checked, including its HTTP status, canonical URL found, and any issues detected. You can filter the table to show only pages with missing canonicals, only pages with duplicate canonicals, or only pages with errors, making it easy to prioritise fixes.

Limitations of the Crawl Mode

The crawl tool reads raw HTML and does not execute JavaScript. Pages that render canonical tags via JavaScript (a common CMS configuration mistake) will appear to have no canonical even if a JS-rendered tag exists. This is actually useful information: if Google's crawler visits before JavaScript executes, it will also see no canonical. Fix this by outputting canonical tags in the server-rendered HTML, not via JavaScript.

Free SEO Tools

More Free SEO Tools from Behind the Search

Every tool you need for technical SEO, on-page optimisation, and content auditing, all free and instant.

🏗

HTML Headings Checker

Audit H1 to H6 hierarchy, detect duplicate headings and level skips.

📊

Keyword Density Calculator

Check density, prominence, bigrams and trigrams for any content or URL.

🔧

Schema Markup Validator

Validate and generate JSON-LD schema for rich result eligibility.

🏷

Meta Tag Checker

Check title, meta description, Open Graph, Twitter Card and more.

🤖

Robots.txt Tester

Test if Googlebot can access any URL based on your robots.txt rules.

Common Questions

Canonical Tags: Frequently Asked Questions

Clear answers to the most common questions about canonical tags, duplicate content, and SEO.

What is the difference between a canonical tag and a 301 redirect?

A 301 redirect physically moves users and bots from one URL to another. The old URL stops working. A canonical tag keeps both URLs accessible but tells Google which one to index and consolidate ranking signals to. Use a 301 redirect when you genuinely want to retire a URL and permanently replace it. Use a canonical tag when you need both URLs to remain accessible (for example, printer-friendly versions, URL parameter variations, or syndicated content) but want one to be the preferred indexed version.

Does Google always follow canonical tags?

Google treats canonical tags as strong hints, not hard directives. In most cases Google follows them, but Google may override your canonical if it determines the signals are conflicting or the canonical target is inappropriate. Common reasons Google ignores a canonical include: the canonical target returns an error, the canonical points to a noindexed page, the content of the two pages is too different, or there are conflicting signals from sitemaps and internal links. This tool checks for many of these conflicts automatically.

Should paginated pages like page 2 and page 3 have a canonical pointing to page 1?

Google's current recommendation is to use self-referencing canonicals on every paginated page, not to canonicalise them all to page 1. Canonicalising page 2 to page 1 tells Google to ignore page 2 entirely, which may hide content that only appears on deeper pages. Instead, use self-referencing canonicals on all paginated pages and make sure your internal linking structure clearly signals to Google that the pages are part of a series.

Can canonical tags hurt my SEO if implemented incorrectly?

Yes. Incorrect canonical tags can cause significant damage. A canonical pointing an important product page to a category page tells Google to index the category instead and ignore the product, removing it from search results. Multiple canonical tags on the same page tell Google to ignore all of them, eliminating the duplicate content protection you intended. Our free canonical checker catches these critical mistakes before they affect your rankings.

How do I check if my canonical tags are working correctly for my whole site?

Use the Website Crawl mode in this free canonical checker. Enter your homepage URL, select up to 50 pages, and the tool will crawl your site, extract the canonical tag from every page it finds, and report the full picture: how many pages are missing canonicals, how many have multiple conflicting canonicals, and which groups of pages are all pointing to the same canonical URL. For very large sites, Google Search Console's Coverage report also shows canonicalisation decisions Google has made.

Behind the Search · Free SEO Tools for Everyone

Stop Losing Rankings to Broken Canonical Tags. Find and Fix Them Free.

Our free canonical tag checker is one of 20+ professional SEO tools built by Behind the Search so every site owner and SEO professional has access to real audit-grade tools without expensive software subscriptions.

Every tool is free, instant, runs server-side on live HTML, and stores no data. No login required. No usage limits.

🛠 View All Free SEO Tools 📖 SEO Learning Hub

Canonical Checks

Pages per Crawl

20+