duplicate-beacon

Detect duplicate and near-duplicate titles, meta descriptions and page bodies across your built static site.

Duplicate content splits ranking signals and makes search engines pick a URL for you. It usually comes from templates: every product page titled "Widgets | Acme", one meta description pasted into twenty pages, a print or AMP copy of every article, tag pages that are 95% the same. duplicate-beacon compares every built page with every other one, skipping pages that are noindex or already canonicalised elsewhere, and reports each group with the files, 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

Titles: exact duplicates, and titles that only differ by the site name once the common | Brand suffix or prefix is removed.
Meta descriptions: exact duplicates, near-duplicates (template text with a word swapped), and descriptions that just repeat the title.
Bodies: identical main content, and near-duplicates using 5-word shingles with MinHash/LSH candidate search and exact Jaccard similarity (--threshold, default 0.9). Navigation, header, footer and aside are left out of the main-content comparison.
Boilerplate: pages whose text is mostly shared with many other pages (info).
Scales to thousands of pages without quadratic body comparisons.
Text/JSON/SARIF/Markdown output, --fail-on, exit codes 0/1/2, allowlist with expiry, severity overrides, GitHub Action with job summary.

Scope

duplicate-beacon compares pages inside one build. Canonical tag correctness is covered by canonical-beacon and repeated H1s by heading-beacon.

Rules

Rule	Default severity	What it means
`duplicate-body`	high	Pages have identical main content
`duplicate-title`	high	Pages share the same <title>
`near-duplicate-body`	medium	Pages have near-identical main content (similarity at or above the threshold)
`duplicate-description`	medium	Pages share the same meta description
`near-duplicate-title`	low	Titles are identical once the shared site-name suffix/prefix is removed
`near-duplicate-description`	low	Meta descriptions are near-identical (template text with one word changed)
`title-equals-description`	low	Meta description just repeats the title
`duplicate-template-heavy`	info	Most of the page text is boilerplate shared with many other pages
`allowlist-expired`	medium	An allowlist entry is past its `expires` date
`allowlist-unused`	info	An allowlist entry matched nothing

Install and run

npx duplicate-beacon dist
npx duplicate-beacon dist --threshold 0.85 --fail-on medium
npx duplicate-beacon public --ignore "/tags/**,/page/*" --min-words 80
npx duplicate-beacon out --format json > duplicates.json

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

duplicate-beacon — /workspace/duplicate-beacon/test/fixtures/bad
11 page(s); 11 compared (noindex and canonicalised pages excluded)

HIGH     b.html 2 pages share the title "Widgets | Acme": /a.html, /b.html [duplicate-title]
         ↳ fix: Give each page a unique, descriptive <title>.
HIGH     b.html 2 pages have identical main content: /a.html, /b.html [duplicate-body]
         ↳ fix: Consolidate them into one page, or point duplicates at the original with rel=canonical (or noindex them).
MEDIUM   b.html 2 pages share the meta description "Buy widgets online from Acme today at low prices.": /a.html, /b.html [duplicate-description]
         ↳ fix: Write a unique description for each page, or remove it and let search engines generate one.
MEDIUM   c.html /a.html and /c.html are 94% similar [near-duplicate-body]

Options

duplicate-beacon 1.0.0 — detect duplicate and near-duplicate titles, descriptions and page bodies

Usage: duplicate-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
      --threshold <0-1>        Similarity for near-duplicate bodies (default 0.9)
      --min-words <n>          Ignore bodies shorter than n words (default 50)
      --ignore <globs>         Pages to leave out of the comparison
      --no-template-check      Do not report boilerplate-heavy pages

Common
  -c, --config <file>     JSON config (default: .duplicate-beacon.json or "duplicateBeacon" 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 .duplicate-beacon.json (or a "duplicateBeacon" key in package.json, or --config <file>):

{
  "failOn": "medium",
  "severity": {
    "duplicate-body": "low"
  },
  "allowlist": [
    {
      "rule": "duplicate-title",
      "subject": "/variants/*",
      "reason": "Colour variants share a title until the PIM migration",
      "expires": "2027-03-31"
    }
  ],
  "threshold": 0.9,
  "minWords": 50,
  "ignore": [
    "/tags/**"
  ]
}

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 .duplicate-beacon.json can live at your repository root. Other keys: threshold, minWords, ignore, descriptionThreshold (default 0.6), "templateCheck": false, templateShare (default 0.3) and templateRatio (default 0.8).

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:
  duplicate-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/duplicate-beacon@v1
        with:
          path: dist
          fail-on: high
          sarif: duplicate-beacon.sarif
      - uses: github/codeql-action/upload-sarif@v3
        if: always()
        with: { sarif_file: duplicate-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, shingles, jaccard } from "duplicate-beacon";
const report = check("dist", { threshold: 0.85 });
jaccard(shingles(a), shingles(b)); // 0..1

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 duplicate-beacon helps you, a link back is appreciated:

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

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

duplicate-beacon