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Canonical URL checker: paste page HTML to audit rel=canonical, og:url and robots meta tags, and compare two URLs for duplicates. Canonical URL Checker — Audit rel=canonical, og:url and robots Tags Without Leaving Your Browser Duplicate content quietly drains rankings, and a broken rel=canonical tag is the most common reason. This canonical URL checker is a lightweight Chrome extension that audits the canonical setup of any page from its pasted HTML source — no crawler, no signup, no access to your browsing data. Paste the markup, click one button, and read a color-coded verdict in seconds. HOW IT WORKS Open the page you want to audit, view its source (Ctrl+U), copy the HTML — the full document or just the <head> section — and paste it into the canonical URL checker popup. Click Check canonical and the canonical URL checker parses the markup locally with the browser's own DOM parser. Every rule in the checklist renders as a green, yellow, or red line, so you can see the health of the page at a glance and copy the whole report to your clipboard for a ticket, an audit document, or a Slack message to your developer. WHAT THE CHECKLIST COVERS Canonical presence — the canonical URL checker confirms whether a <link rel="canonical"> tag exists at all. A missing tag lets search engines pick the canonical themselves, which is rarely what you want. Absolute URL — relative canonical paths are a classic footgun. The canonical URL checker flags any href that does not start with a full protocol and domain. HTTPS protocol — if the canonical still points at the insecure http:// version of the site, the canonical URL checker raises a warning so you can fix the mixed-protocol signal. Duplicate tags — two or more canonical tags send conflicting signals and search engines may ignore all of them. The canonical URL checker counts every tag and warns you when it finds more than one. og:url consistency — the canonical URL checker locates the Open Graph og:url meta tag and tells you whether it matches the canonical after normalization. A mismatch means social shares and search may point at different addresses. Meta robots — a stray noindex directive silently removes a page from search results. The canonical URL checker surfaces it in red so an accidental deploy of staging settings never goes unnoticed again. COMPARE URLS TAB The second tab answers a question every SEO asks daily: do these two addresses resolve to the same canonical target? Paste two URLs and the canonical URL checker normalizes both — it unifies the protocol, strips the www prefix, removes the trailing slash, and drops tracking parameters such as utm_source, utm_medium, utm_campaign, and fbclid. You get a clear verdict, same target or different, together with both normalized forms so you can see exactly why. Use it to decide whether a redirect is needed, to deduplicate URL lists from analytics exports, or to verify that campaign links with tracking parameters collapse into one canonical page. WHY ZERO PERMISSIONS MATTER Most SEO extensions demand access to every website you visit. This canonical URL checker requests no permissions at all. It cannot read your open tabs, cannot inject scripts into pages, cannot see your history, and never sends a single byte to any server. All parsing happens inside the popup with plain JavaScript, fully offline. There is no analytics code, no advertising library, no third-party SDK. Client HTML from a confidential audit stays on your machine — a real advantage when you work under NDA. WHO IS IT FOR Technical SEO specialists running site audits who need a fast second opinion on a single page. Content managers checking that a freshly published article carries the right canonical before it gets indexed. Developers verifying template changes in code review, where pasting generated HTML into the canonical URL checker is faster than deploying to staging. Agencies preparing audit reports who want a copy-ready checklist for every page. Students learning technical SEO who want to see how rel=canonical, og:url, and meta robots interact on real pages. If duplicate content is on your radar, this canonical URL checker belongs in your toolbar. GETTING STARTED Pin the Canonical URL Checker icon to your Chrome toolbar. Click it, paste the HTML of any page, press Check canonical, and read the color-coded report. Switch to the Compare URLs tab whenever you need to test two addresses against each other. The whole flow takes under ten seconds. Install the canonical URL checker now and catch canonical mistakes before search engines do.