About CanonicalTag.com and Bill Hartzer

CanonicalTag.com is an independent reference for one small piece of HTML with an outsized effect: the canonical tag, rel="canonical". It decides which URL a search engine should index when the same content is reachable at several addresses, and when it is wrong the damage is quiet. Ranking signals split across duplicates, the page you wanted indexed drops out, and Search Console fills with statuses that read like errors but often are not.

Who writes it

I am Bill Hartzer, and I write and edit every page on this site. I have been working in search since 1996, and my consulting practice, Hartzer Consulting, focuses on technical SEO, website and domain migrations, and search engine marketing. I also founded DNAccess, which works on domain recovery and registrar security, and I serve as an expert witness in matters involving SEO, online advertising and domain names.

Canonicalization is where much of that work meets. A migration that changes hosts, protocols or URL structures is, underneath, a canonicalization problem: every old URL has to hand its signals to exactly one new URL, and every signal on the site has to agree about which one that is. Diagnosing canonicalization problems on client sites is a regular part of that work, and this site is the reference I wanted for explaining them.

What the site covers, and what it does not

The site covers the canonical tag itself, the Google Search Console statuses it produces, the sources of duplicate URLs (hosts, redirects, parameters, product variants, AMP and mobile URLs), the signals that interact with it (redirects, noindex, robots.txt, hreflang) and how canonical tags work on more than twenty platforms. It deliberately does not cover the wider set of SEO head tags, so each page can go deep on one subject.

If you are starting from a Search Console report, the canonical issues and fixes index is the quickest way in; if you are setting up a site, canonical tags by platform covers each system, and the guide to common canonical tag mistakes is the fastest audit of an existing setup. Short definitions live in the glossary, quick answers in the canonical tag FAQ, and the topic groups page lays out the whole reference.

Nothing is for sale here. There are no sponsored pages, no affiliate links and no vendor rankings; when a plugin or tool is named, it is named as an example. The free tools on the site store nothing you enter.

How pages are researched

Every page starts from sourced research, mostly Google Search Central documentation, Search Console Help, the relevant RFCs and each platform's own documentation, and every figure and setting name is traced to a document before it is published. The full process, including how dates work and what happens when sources disagree, is on the methodology page.

Independence

CanonicalTag.com is not affiliated with Google or with any platform, plugin or product described on it. Product names are used for identification. Search engine behavior changes, so each page links to the primary documentation it relies on; if you find something that has changed, the contact page reaches me directly.