Canonical Tag Checker

WHAT IT DOES

Canonical Tag Checker scans the current page for rel="canonical" link tags and reports everything you need to know. It displays the canonical URL, compares it to the current page URL, and detects common issues: missing canonical tags, multiple canonical tags, relative URLs (should be absolute), HTTP/HTTPS mismatches, domain mismatches, trailing slash differences, and potential redirect chains. Each issue comes with a clear explanation and severity level (error, warning, or info) so you know what needs fixing. Perfect for SEO audits, content migration validation, and ensuring duplicate content is properly consolidated.

WHERE IT RUNS

Any webpage—the script scans the page's head for canonical link tags. No server-side calls, no external dependencies, no site-specific configuration. Works on local files, development environments, production sites, and pages behind authentication. The analysis is entirely client-side using standard DOM APIs.

HOW TO USE

Install the script and open any page. The panel automatically checks for canonical tags and displays the results. The summary shows the status (Valid, Warnings, or Issues), the number of canonical tags found, and the total issues detected. Toggle "Show warnings" to include or exclude warning-level issues from the report. Click "Check Now" to re-scan—useful for pages where the canonical tag is added dynamically. Click "Copy Report" to copy the full canonical tag report to your clipboard for documentation or sharing. Keyboard shortcut: Ctrl+Shift+C to re-scan without opening the panel.

TECHNICAL MECHANISM

The script scans the page using document.querySelectorAll('link[rel="canonical"]') to find all canonical tags. For each tag, it reads the href attribute and resolves relative URLs using new URL(href, window.location.origin). It then performs a series of checks: counts the number of tags (missing or multiple), detects relative URLs (not starting with http://, https://, or //), compares protocols (HTTP vs HTTPS), compares domains (same or different), compares normalized URLs (removing trailing slashes), and checks for trailing slash mismatches. Normalization uses the URL API to parse and compare components. Issue severity is determined by the potential SEO impact—missing tags and domain mismatches are errors, protocol mismatches and trailing slash differences are warnings, and intentional differences are marked as info. The report includes the current page URL, all discovered canonical URLs (with the first marked as primary), and a filtered list of issues.

THE PANEL

The tool runs inside BGPanel, a lightweight UI system built into the BotGentz extension. Drag the panel by its header to reposition it anywhere on screen—it snaps to edges and remembers its position per site. Click the header to collapse the panel into a small bubble; click again to expand. Resize the panel by dragging its bottom-right corner. Press Escape at any time to close the panel. The panel stays out of your way but is always accessible via the extension's toolbar.

PLEASE NOTE

Requires the free BotGentz browser extension to run—this script does not work standalone. The script reads only the page's link tags—it does not send data anywhere, does not store page content, and does not access other tabs or browser history. The analysis is based solely on what is in the HTML; it does not verify that the canonical URL actually resolves or returns a 200 status code. Redirect chains are flagged as informational—the script does not perform network requests to check redirects due to CORS and performance constraints. Sites that inject canonical tags via JavaScript may not be detected until after the page has fully rendered; use the "Check Now" button to re-scan after dynamic content loads. Sites change over time, but this script relies on standard DOM APIs, not site-specific selectors, so it remains robust across most pages.