SEO Technical: Canonical

Guides canonical tag configuration to consolidate duplicate content and declare preferred URLs.

When invoking: On first use, if helpful, open with 1–2 sentences on what this skill covers and why it matters, then provide the main output. On subsequent use or when the user asks to skip, go directly to the main output.

Scope (Technical SEO)

• Duplicate site versions: HTTPS vs HTTP; www vs non-www; trailing slash (/page vs /page/) — choose one, 301 redirect others

• Duplicate content: Canonical tags; consolidate and 301 to preferred URL

• HTTPS: SSL/TLS; secure connection; ranking signal since 2014

Initial Assessment

Check for project context first: If .claude/project-context.md or .cursor/project-context.md exists, read it for site URL and language structure.

Identify:

• Site URL: Base domain

• Duplicate scenarios: Multi-language, query params, pagination, alternate URLs

• Framework: Next.js, React, static, etc.

Canonicalization Methods (Choose by Scenario)

Method When Strength

301 redirect Preferred; server can redirect Strongest — permanent redirect

Canonical tag Cannot redirect (e.g. params, pagination) Strong — HTML signal

robots.txt Block non-canonical paths Weak — advisory only

Use 301 for HTTP→HTTPS, www variants, trailing slash. Use canonical for params, pagination, UTM.

HTTPS & Security

HTTPS is a ranking signal (Google, 2014). Users and crawlers should access only the HTTPS version.

Requirement Action

SSL/TLS certificate Install valid certificate; use Let's Encrypt for free

301 redirect HTTP → HTTPS; all HTTP requests redirect to HTTPS

Mixed content No HTTP resources on HTTPS pages; fix mixed content warnings

HSTS Optional; Strict-Transport-Security header for repeat visitors

WWW vs non-WWW: Choose one preferred version; 301 redirect the other. See canonical rules above.

When to Use Canonical

• Multi-language: Each language version has its own canonical; use hreflang with canonical

• Same content, multiple URLs: Params, pagination, tracking params, www vs non-www, trailing slash (/page vs /page/)

• Self-referencing: Canonical should point to self or the preferred version

• Avoid chain canonical: A→B→C is invalid

Rules

Rule Note

Absolute URL Include https://

Consistency Must match current page URL or the chosen preferred version

No chains A→B→C is invalid

Implementation Patterns

Next.js (metadata)

export const metadata = { alternates: { canonical: "https://example.com/page-slug", languages: { zh: "https://example.com/zh/page-slug", en: "https://example.com/page-slug", "x-default": "https://example.com/page-slug", }, }, };

HTML (generic)

<link rel="canonical" href="https://example.com/page-slug" />

Server Redirects (301)

Apache (.htaccess):

RewriteEngine On RewriteCond %{HTTPS} off RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

Nginx:

return 301 https://$host$request_uri;

Relationship to Other Technical SEO

• Sitemap: URLs in sitemap should match canonical

• IndexNow: Submit canonical URLs

Output Format

• Canonical URL for each page type

• Implementation (metadata or HTML)

• Multi-language setup if applicable

• References: Alignify URL optimization; Google Canonical

Related Skills

• url-structure: URL hierarchy and format; canonical handles duplicate variants (HTTPS, www, trailing slash)

• localization-strategy: hreflang + canonical for multi-language

• xml-sitemap: Sitemap URLs should match canonical

• indexnow: Submit canonical URLs

• google-search-console: Find duplicate content in Coverage report

• indexing: Resolve indexing issues

• site-crawlability: Crawl budget; redirect chains; canonical reduces duplicate crawl waste