When should I use a canonical tag?

When the same content lives at multiple URLs (sorted/filtered listings, tracking-parameter URLs, http vs. https). It tells search engines which URL to index.

Is the URL I enter sent anywhere?

No. The tags are built in your browser; nothing is transmitted.

Can I self-canonical?

Yes, and it's recommended. A page with rel="canonical" pointing to itself prevents query-string variants from creating duplicates in the index.

Does canonical work across domains?

Yes. You can canonicalize to a URL on another domain you own. Google treats it as a strong hint, but cross-domain canonical is sometimes ignored if signals conflict.

canonical · alternate · amphtml · seo

Generate canonical and alternate link tags

Build the rel=canonical link plus rel=alternate variants for mobile, AMP and other media. Markup assembly runs locally in your browser.

Canonical URL Generator

Canonical

set

primary

Alternates

variants

Length

194 B

194 chars

Status

ready

live

input · urls

Canonical URLAlternates — one per line, optional (media: …) or (amphtml)

output · link tags

<link rel="canonical" href="https://example.com/article">
<link rel="alternate" media="handheld" href="https://m.example.com/article">
<link rel="amphtml" href="https://example.com/article.amp">

Quick Start

How to declare canonical URLs

Canonical URLs tell search engines which version of duplicate-or-near-duplicate pages is the master. Alternates point to localized, mobile or AMP variants.

01
Set canonical
Paste the absolute master URL — same protocol, host and path you want indexed.
Lookups reference the IANA registries (MIME, HTTP status, TLDs) bundled at build time — no live network calls, no rate limits, no leaked queries.
canonicalIANAregistryofflinelive
canonical · queryset · IANA
```
<link rel="canonical" …>
```
loaded · IANA bundlespec · ready
02
Add alternates
One URL per line. Use (media: handheld) for mobile or (amphtml) for AMP.
Builders emit canonical syntax per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs) so the output passes spec-compliant parsers.
alternateRFC 9110canonicalspec-compliantlive
alt · optionsmedia · live
```
<link rel="alternate" media="…" …>
```
options applied · livecanonical
03
Inspect output
Generated tags reflect changes live — no rebuild required.
Validation flags common pitfalls — uppercase header names, smart quotes inside Content-Type, missing ;charset=utf-8 — before they bite production.
livevalidationlintpitfalls
out · looked uphtml · ready
```
<link rel="amphtml" …>
```
result · livevalidated
04
Drop into head
Place the tags inside <head> before the body for crawlers to find first.
Copy writes the snippet directly into your clipboard; downloads emit the right extension and MIME so curl/httpie pick them up correctly.
shipclipboardMIME-correctblobcurl-ready
ok · copiedhead · done
```
✓ Copied
```
shipped · ready to shipsuccess

Pro tips

Web-spec details that bite later

Idempotency saves retries

POST/PUT/DELETE should be safely retried. Use idempotency keys and return the same response on duplicate requests.

Match RFC 9110 status codes

Don’t invent codes. 422 for validation errors, 409 for conflicts, 429 for rate limits. Standard codes work with off-the-shelf clients.

Set <code>Cache-Control</code> deliberately

Default browser caching is conservative. Use max-age + stale-while-revalidate for hot endpoints.

Validate Open Graph in dev

OG tags break silently. Use a previewer like OG Generator + Facebook’s debugger before launch.

CORS is a server concern

The browser sends the preflight; the server decides. Wildcard origins disable credentials — be explicit.

MIME drives behaviour

Servers must send the right Content-Type. Browsers sniff but the spec says they shouldn’t — be explicit to avoid surprises.

Use Cases

When to set canonical URLs

SEO consolidation, mobile pairing, AMP linking.

Duplicate content

Tracking parameters or sort orders create duplicate URLs — pick one master. Bundled from IANA registries at build time — no live network call, no rate limit, no leaked queries. The MIME, TLD, and status-code tables are baked in so the tool works offline once loaded.

spec-compliant

Mobile pairing

Link desktop and m.dot mobile variants with rel=alternate. Output is canonical per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs), so spec-compliant parsers accept it as-is. Cross-browser and cross-library behaviour stays consistent.

offline

AMP

Connect canonical HTML page with its AMP version. Pairs with the curl-to-fetch converter for end-to-end test stubs — copy the curl from DevTools, paste, get an idiomatic fetch() body. Drop into Playwright/Vitest fixtures without manual translation.

IANA-backed

Pagination

Point every page in a series at the master listing. Catches common pitfalls (uppercase header names, smart quotes inside Content-Type, missing ;charset=utf-8) before they bite production. Validation flags rather than auto-corrects so you stay in control.

RFC-aligned

Migration

During a rename, canonicals consolidate link equity. Validation runs as you type — copy only when the output is shaped correctly. The output drops directly into nginx, Apache, or CDN configs without re-formatting or re-quoting.

production-grade

Syndication

Republished articles canonical-back to the original. Same input plus same options always produces identical canonical output, so the tool is safe to embed in CI scripts that diff against expected configs.

curl-ready

FAQ

Frequently asked questions

Self-referential canonical?

Yes — Google explicitly recommends every page declare its own URL as canonical to avoid ambiguity.

Relative or absolute?

Always absolute, including protocol. Relative canonicals are valid but error-prone.

Canonical vs 301?

A 301 redirect is stronger — use it when consolidating permanently. Canonicals are hints for crawlers.

Will canonicals fix duplicate content?

They consolidate ranking signals to the master URL, but the duplicates still get crawled — better to remove them.

Is anything sent to a server?

No — markup is assembled locally in your browser.

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