canonical-beacon

Check canonical tags and hreflang clusters in your built static site: one canonical per page, pointing at a real, indexable, final URL, and hreflang clusters that are valid, self-referencing and reciprocal.

Canonical and hreflang mistakes are silent. A template ships two canonicals, a page canonicalises to a URL that was renamed, a translated page points hreflang at an English page that never links back, or a region is written en-UK. Search engines then ignore the hints, index the wrong URL or show the wrong language. canonical-beacon reads the built HTML (plus Link headers from _headers/vercel.json) and checks every canonical and hreflang annotation against the other pages in the build. Each finding has the file, line, severity and a concrete fix.

CLI, library and GitHub Action. Node.js 18+, zero runtime dependencies. Works on any static build output (Astro, Next.js output: 'export', Eleventy, Hugo, Jekyll, Docusaurus, VitePress, plain HTML) and runs offline: point it at the folder your build writes. By Louis Wright.

Features

• Canonical tags: missing, more than one, empty or invalid, relative, outside <head>, tracking parameters or #fragment, og:url and Link header disagreements.
• Canonical targets: the target page must exist in the build, must not be a 404 page or meta-refresh stub, must not be noindex, and must not canonicalise somewhere else again (chains). Cross-host and http/https canonicals are flagged unless you allow cross-domain canonicals.
• Mixed signals: a noindex page that also canonicalises to another URL.
• hreflang codes: ISO 639-1 language with optional script and ISO 3166-1 / UN M.49 region (en-GB, zh-Hant-TW, es-419) or x-default; catches en-UK, en_GB and region-only codes.
• hreflang clusters: self-reference, return links (reciprocity), duplicate codes, relative hrefs, alternates that are missing, noindex or non-canonical, hreflang on non-canonical pages, x-default presence, and <html lang> agreeing with the page’s own code.
• Text/JSON/SARIF/Markdown output, --fail-on, exit codes 0/1/2, allowlist with expiry, severity overrides, GitHub Action with job summary.

Scope

canonical-beacon does not crawl the live site, follow HTTP redirects or check broken links; use redirect-sentinel and static-link-sentinel for those. Alternates on other domains are accepted but cannot be verified offline.

Rules

| Rule | Default severity | What it means | |---|---|---| | canonical-missing | medium | Page has no rel=canonical | | canonical-multiple | high | Page declares more than one different canonical URL | | canonical-invalid | high | Canonical href is empty, unparsable or not http(s) | | canonical-relative | low | Canonical href is relative (absolute URLs are recommended) | | canonical-in-body | high | rel=canonical is outside , so search engines ignore it | | canonical-other-host | medium | Canonical points to another host or protocol | | canonical-target-missing | high | Canonical target has no page in the build | | canonical-target-not-final | high | Canonical target is an error page or meta-refresh stub | | canonical-target-noindex | high | Canonical target is noindex | | canonical-chain | medium | Canonical target itself canonicalises somewhere else | | canonical-noindex-conflict | medium | Page is noindex and also canonicalises to another URL (mixed signals) | | canonical-has-query-or-fragment | low | Canonical URL contains a #fragment or tracking query parameters | | canonical-og-url-mismatch | low | og:url differs from the canonical URL | | canonical-header-mismatch | medium | Link: rel=canonical header disagrees with the HTML canonical | | hreflang-invalid-code | high | hreflang value is not a valid language(-region) code or x-default | | hreflang-duplicate-code | high | Same hreflang code points to different URLs | | hreflang-no-self | medium | hreflang cluster does not include the page itself | | hreflang-no-return | high | Alternate page does not link back (non-reciprocal hreflang) | | hreflang-target-missing | high | hreflang alternate has no page in the build | | hreflang-target-non-canonical | high | hreflang alternate is noindex or canonicalises elsewhere | | hreflang-on-non-canonical | medium | Page with hreflang canonicalises elsewhere | | hreflang-relative | medium | hreflang href is relative (must be fully-qualified) | | hreflang-no-x-default | info | hreflang cluster has no x-default | | hreflang-lang-mismatch | low | Page does not match its own hreflang code | | hreflang-in-body | high | hreflang link is outside | | allowlist-expired | medium | An allowlist entry is past its expires date | | allowlist-unused | info | An allowlist entry matched nothing |

Install and run

npx canonical-beacon dist
npx canonical-beacon dist --base-url https://example.com --fail-on medium
npx canonical-beacon out --clean-urls --exclude "/drafts/**"
npx canonical-beacon public --allow-cross-domain --format sarif > canonical.sarif

Pages are mapped to URLs the way static hosts serve them: index.html → /, blog/index.html → /blog/, about.html → /about.html (or /about with --clean-urls). Pass --base-url with your public URL, or let it be inferred from canonical / og:url tags. Meta-refresh redirect stubs and 404.html are skipped. X-Robots-Tag and Link headers are read from Netlify/Cloudflare _headers and vercel.json.

Sample output

canonical-beacon — https://example.com
11 page(s); 9 with canonical, 2 with hreflang at https://example.com

HIGH     a.html:1 /a.html declares 2 canonicals: https://example.com/a.html, https://example.com/b.html [canonical-multiple]
         ↳ fix: Keep exactly one rel=canonical; search engines may ignore all of them otherwise.
HIGH     c.html:1 Canonical https://example.com/d.html is noindex [canonical-target-noindex]
         ↳ fix: Canonicalise to an indexable page, or remove noindex from the target.
HIGH     e.html:1 /e.html declares 2 canonicals: https://example.com/gone.html, https://example.com/e.html [canonical-multiple]
         ↳ fix: Keep exactly one rel=canonical; search engines may ignore all of them otherwise.
HIGH     e.html:1 rel=canonical on line 1 is outside <head> [canonical-in-body]
         ↳ fix: Move it into <head>.
HIGH     e.html:1 Canonical https://example.com/gone.html has no page in the build [canonical-target-missing]

Options

canonical-beacon 1.0.0 — check canonical tags and hreflang clusters in your built static site

Usage: canonical-beacon [site-dir] [options]

Site
      --base-url <url>        Public URL of the site, e.g. https://example.com (default: inferred from canonical/og:url)
      --include <globs>       Only check these pages (file or URL path globs, comma-separated)
      --exclude <globs>       Skip these pages
      --clean-urls            Pages are served without .html (about.html -> /about)
Checks
      --no-require-canonical   Do not report pages without rel=canonical
      --allow-cross-domain     Accept canonicals that point to another host

Common
  -c, --config <file>     JSON config (default: .canonical-beacon.json or "canonicalBeacon" in package.json)
  -f, --format <fmt>      text (default) | json | sarif | markdown
      --json <file>       Also write a JSON report
      --sarif <file>      Also write SARIF 2.1.0
      --markdown <file>   Also write Markdown (e.g. for a job summary)
      --fail-on <sev>     critical | high | medium | low | info | none (default: high)
      --list-rules        Print rules and default severities
      --no-fixes          Hide fix suggestions in text output
      --no-color          Disable colours
  -v, --version / -h, --help

Exit codes: 0 = passed, 1 = findings at or above --fail-on, 2 = usage, config or read error.

Configuration and allowlist

Options can live in .canonical-beacon.json (or a "canonicalBeacon" key in package.json, or --config <file>):

{
  "failOn": "medium",
  "severity": {
    "canonical-missing": "low"
  },
  "allowlist": [
    {
      "rule": "canonical-missing",
      "subject": "/legacy/*",
      "reason": "Legacy pages are being migrated",
      "expires": "2027-03-31"
    }
  ],
  "requireCanonical": true,
  "allowCrossDomain": false,
  "xDefaultOptional": false
}

• severity changes a rule's severity, or turns it "off".
• allowlist entries suppress matching findings. Each needs a reason and matches on any combination of rule, file, subject (globs with *) and match (a substring of the message). Add expires (YYYY-MM-DD) so the exception is time-boxed: once it lapses the finding comes back along with an allowlist-expired finding (medium). Entries that no longer match anything are reported as allowlist-unused (info).

Config can also set baseUrl, include, exclude and cleanUrls. The config file is looked up in the site directory first, then in the current directory, so .canonical-beacon.json can live at your repository root. Other keys: requireCanonical (default true), allowCrossDomain (default false) and xDefaultOptional (default false; set true to silence hreflang-no-x-default).

Output and exit codes

• --format text (default), json, sarif (SARIF 2.1.0 for GitHub code scanning) or markdown (for job summaries and PR comments). --json, --sarif and --markdown write extra report files in the same run.
• --fail-on <severity> sets the threshold (critical, high, medium, low, info, none; default high).
• Exit codes: 0 passed, 1 findings at or above --fail-on, 2 usage, config or read error.

GitHub Action

permissions:
  contents: read
  security-events: write   # only needed for the SARIF upload
jobs:
  canonical-beacon:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
        with: { persist-credentials: false }
      - run: npm ci && npm run build   # produce the static site first
      - uses: MrLouisWright/canonical-beacon@v1
        with:
          path: dist
          fail-on: high
          sarif: canonical-beacon.sarif
      - uses: github/codeql-action/upload-sarif@v3
        if: always()
        with: { sarif_file: canonical-beacon.sarif }

| Input | Description | Default | |---|---|---| | path | Built site directory (e.g. dist, public, _site) | . | | base-url | Public URL of the site, e.g. https://example.com | | | fail-on | Failure threshold | high | | config | Config file path | | | sarif / json | Write SARIF / JSON report to this path | | | job-summary | Add the Markdown report to the job summary | true | | args | Extra CLI arguments | |

The action runs the bundled CLI with Node 20; it has no dependencies to install. Pin it to a commit SHA if your policy requires it.

Library

import { check, validHreflang } from "canonical-beacon";
const report = check("dist", { baseUrl: "https://example.com" });
console.log(report.counts, report.findings[0]);
validHreflang("en-UK"); // { ok: false, reason: ... }

Types are included.

Requirements

Node.js 18 or newer. Zero runtime dependencies.

Support

If this project is useful to you, you can support its development with a donation: Buy me a coffee. It helps keep these tools maintained, documented and free for everyone.

Credit (optional)

Free to use under MIT, no attribution required. If canonical-beacon helps you, a link back is appreciated:

<a href="https://louiswright.co.uk">Built with canonical-beacon by Louis Wright</a>

[![Built with canonical-beacon by Louis Wright](https://img.shields.io/badge/built%20with-canonical--beacon-blue)](https://louiswright.co.uk)

Licence

MIT © Louis Wright (Louis Wright)