canonical-tag
Audit and fix duplicate-page canonicalization across protocol, host, slash, default-document, extension, case, and tracking-parameter URL variants. Use for canonical URLs, duplicate content, preferred URLs, URL consolidation, or conflicting canonical signals. For URL naming and hierarchy design, use url-structure.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/kostja94/marketing-skills --skill canonical-tag- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads canonical-tag automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
SEO Technical: Canonicalization
Determine the preferred URL for each page identity, consolidate duplicate variants, and verify that redirects, canonical annotations, internal links, sitemaps, and localization signals agree.
Scope
Treat these as one duplicate-page canonicalization problem when they expose the same or substantially similar primary content:
- HTTP and HTTPS;
- www and non-www hosts, including combined protocol/host variants;
- trailing-slash and non-trailing-slash paths;
- repeated path slashes such as
/docs//guide; - directory defaults such as
/docs/and/docs/index.html; - historical extensions such as
/guide.htmland/guide; - case variants such as
/Guideand/guide; - UTM and other tracking parameters that do not change primary content.
Do not assume that similar-looking URLs are duplicates. Case, parameters, extensions, and slash behavior can identify different resources. Compare response behavior, primary content, and project intent before consolidating.
Inputs and Context
Read root contextus.md when present and only the modules relevant to the task. Otherwise use project configuration, routing code, deployment rules, sitemaps, and user-provided facts. Establish:
- preferred scheme and host;
- preferred path conventions;
- which parameters change content versus only attribution or presentation;
- framework, origin server, CDN, and redirect ownership;
- existing indexed URLs, backlinks, migrations, and localization rules when relevant.
Ask only for missing information that would change the preferred URL or make a redirect unsafe.
Decision Rules
| Situation | Primary action |
|---|---|
| Duplicate URL should no longer remain accessible | Permanent server-side redirect to the final preferred URL |
| Duplicate or near-duplicate must remain accessible | rel="canonical" to the preferred URL |
| Canonical HTML page | Self-referencing canonical |
| Non-HTML duplicate such as a PDF | Canonical HTTP Link header when supported |
| Tracking parameter that must reach analytics | Keep the landing request if needed; canonical to the content URL without tracking parameters |
| Parameter changes primary content or search intent | Evaluate as a separate page; do not strip or canonicalize mechanically |
| Pagination | Give each page a crawlable URL and evaluate it as distinct content; do not canonicalize every page to page 1 |
| Language or regional variant | Canonical within the appropriate language identity and coordinate with hreflang |
Use redirects to retire duplicate access paths. Use canonical annotations when access must remain. Do not use robots.txt, the removal tool, or noindex as substitutes for canonicalization.
Variant Audit Matrix
Generate applicable test cases from the real site rather than testing one example only.
| Dimension | Variants to test | Expected invariant |
|---|---|---|
| Scheme | http, https | Non-preferred scheme reaches preferred HTTPS URL |
| Host | www, apex, known aliases | Non-preferred hosts reach one preferred host |
| Scheme + host | all supported combinations | Each duplicate reaches the same final URL without a redirect chain |
| Trailing slash | /page, /page/ | One convention for the same page identity |
| Repeated slash | /a//b, /a/b | Duplicate path normalizes without corrupting :// |
| Default document | /, /index.html; /docs/, /docs/index.html | Default-document aliases converge when content is equivalent |
| Extension | /guide.html, /guide | Historical alias maps to the corresponding page, not the homepage |
| Case | /Guide, /guide | Equivalent paths converge; genuinely case-distinct resources remain distinct |
| Tracking | base URL plus utm_*, gclid, or project tracking keys | Attribution works as required; content identity remains the clean URL |
| Combinations | case + extension + tracking + host/scheme variants | Normalize directly to one destination where safe |
Do not invent routes or send mutation requests during an audit. Use read-only requests unless the user asks to implement fixes.
Signal Consistency
For every preferred URL, verify:
- redirect targets, HTML canonical or canonical HTTP header;
- internal navigation and content links;
- XML sitemap entries;
hreflangURLs and return links when applicable;- structured-data URLs and feeds when they identify the page;
- framework-generated metadata and client-side code do not overwrite the source canonical.
Canonical targets must be absolute, fetchable, indexable, and appropriate for the same content identity. Avoid canonical chains and conflicting targets across methods.
Verification
Record evidence for representative URLs and high-risk templates:
- requested URL;
- HTTP status and each redirect hop;
- final URL;
- source canonical target;
- indexability and content-equivalence result;
- sitemap, internal-link, and
hreflangconsistency; - pass, fail, or needs-decision status.
Confirm that retired variants reach their corresponding preferred page in one hop where infrastructure permits. A final 200 alone is insufficient: the final URL and canonical must also be correct. For Google-specific diagnosis, compare the user-declared and Google-selected canonicals in URL Inspection when access is available.
Implementation Boundaries
Implement in the layer that owns the behavior: CDN or reverse proxy for host/scheme normalization, server/router for paths, and page metadata for canonical annotations. Preserve query parameters needed for attribution or product behavior; remove only parameters confirmed not to affect the destination.
When changing live URLs, provide a mapping and rollback-aware implementation plan. Do not apply redirects to production, alter DNS, or change indexing controls without the user's authorization.
Output
Return:
- the preferred scheme, host, and path conventions;
- duplicate clusters and the evidence that they represent the same page;
- a variant matrix with current and expected behavior;
- the selected method for each cluster: redirect, canonical, separate page, or needs decision;
- implementation location and exact proposed change when requested;
- verification results and unresolved risks.
References: Google canonicalization, canonical methods, redirects, and URL structure.
Related Skills
- url-structure: Design readable hierarchy and format for new canonical URLs.
- localization-strategy: Coordinate canonical and
hreflangfor localized pages. - xml-sitemap: Publish only canonical indexable URLs.
- indexing: Diagnose indexability and selected-canonical issues.
- site-crawlability: Inspect crawl waste, redirect chains, and response behavior.
- google-search-console: Inspect Google-selected canonicals when property access exists.
FAQ
What does the canonical-tag skill do?
Audit and fix duplicate-page canonicalization across protocol, host, slash, default-document, extension, case, and tracking-parameter URL variants. Use for canonical URLs, duplicate content, preferred URLs, URL consolidation, or conflicting canonical signals. For URL naming and hierarchy design, use url-structure.
How do I install canonical-tag?
Run npx skills add https://github.com/kostja94/marketing-skills --skill canonical-tag in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/canonical-tag/ (personal) or .claude/skills/canonical-tag/ (project).
Which AI agents can use canonical-tag?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is canonical-tag safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains canonical-tag?
It is published by kostja94 in kostja94/marketing-skills. It has 1,146 recorded installs.
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