SSD-0009 · Status: stable · Version 1.0 · Reviewed 12 November 2026 · Wikidata Q1033568
Definition
A canonical URL is the single address a publisher declares — through a link element or an HTTP header — as the version a search engine should treat as authoritative when the same content is reachable at several URLs.
標準網址是指當同一內容可以透過多個網址到達時，發佈者透過 link 元素或 HTTP 標頭所宣告、希望搜尋引擎視為權威版本的那一個網址。
In practice
Duplication is normal, not a fault: tracking parameters, print versions, pagination, http versus https, www versus non-www, and product variants all multiply URLs. rel="canonical" is a hint, not a directive — an engine may ignore it when the two pages differ substantially. Two failure modes matter. A self-referencing canonical that points at a URL which then redirects creates a loop of conflicting signals. And a canonical applied site-wide by a template can silently collapse genuinely distinct pages into one, which looks like a ranking drop but is an indexing decision.
重複是常態，不是錯誤：追蹤參數、列印版、分頁、http 與 https、www 與非 www、產品變體，都會令網址倍增。rel="canonical" 是提示，不是指令——若兩頁差異太大，引擎可以不理。兩種失效模式最要緊：自我指向的 canonical 若指向一個會轉址的網址，會造成信號衝突的迴圈；而由範本全站套用的 canonical，可以無聲地把真正不同的頁面壓成一個，表面看像排名下跌，實際是索引決定。
What it is not
- Not a redirect. A redirect moves visitors and bots; a canonical consolidates signals while both URLs still resolve.
- Not a guarantee. It is advisory, and it is ignored when the content does not support the claim.
- Not only for your own duplicates. It also applies across domains you control, such as syndicated articles and regional storefronts.
Status
Stable. The mechanism and its semantics have not changed since it was introduced in 2009. What changes is the volume of accidental duplication that modern site architecture generates.
Identity
- Wikidata: Q1033568 — canonical link element
- English aliases: canonical tag; rel=canonical; canonical link element
- 中文正名：標準網址（香港、台灣）；中國大陸作「规范网址」
- Primary official source: Google: consolidate duplicate URLs
Related terms
Sources
- Google Search Central, “How to specify a canonical URL”, developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls (accessed 12 November 2026).
- Wikidata, item Q1033568 “canonical link element” (accessed 12 November 2026).