Does duplicate content cause a Google penalty?

No. Search engines consolidate rather than penalise: they index one URL, drop the others from results and merge the signals onto the chosen version. The damage is losing control of which URL ranks and splitting internal links and backlinks across copies.

What is the fastest way to check a site for duplicate content?

Crawl the site and look at duplicate titles, duplicate meta descriptions and pages sharing a canonical. Then compare that with the Pages report in Search Console, which shows which URL Google actually selected as canonical.

When should I use a canonical and when a 301 redirect?

Use a 301 when the duplicate URL has no reason to exist, for example an old domain or a www variant. Use a canonical when both URLs need to stay reachable, for example a filtered or parameterised version of a category page.

Does Deltio compare page text to find duplicates?

No. Deltio does not do content similarity comparison. It checks the canonical tag on every URL and reports it missing, invalid or duplicated, and it flags when the value changes between two scans, which is what usually breaks after a deploy.

Will Deltio alert me if a canonical tag changes?

Yes. The SEO scanner compares consecutive scans, so a canonical that changes, disappears or starts appearing twice is reported as a change. Alerts arrive by email and Slack, in your language.

How much does Deltio cost?

Starter is £24 a month, or £20 a month billed annually. Professional is £49 a month and Enterprise is £119 a month. All plans include a 14-day free trial.

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Duplicate Content: How to Check for It and Keep It Fixed

To check a site for duplicate content, look for the same page reachable at more than one URL: parameters, http and https, www and non-www, pagination, print versions, a staging domain left indexable. A crawler finds the copies, and the canonical tag decides which version counts. Google does not penalise duplicate content, it picks one URL and ignores the rest, which is fine until it picks the wrong one. Deltio does not compare page text, it watches the canonical on every URL and alerts you when one goes missing, turns invalid, appears twice or quietly changes. From £20 a month, with a 14-day free trial.

Duplicate content is rarely a writing problem. On a client site it is an architecture problem: the CMS, the shop, the filters or a migration produced several addresses for one page, and nobody told search engines which one to keep. The audit finds it once. Keeping it fixed is the harder part.

What counts, and what does not

There is no duplicate content penalty. When search engines see near-identical pages they consolidate: one URL is indexed, the others are dropped from results, and the signals are merged onto the chosen one. The cost is indirect but real: you lose control of which URL ranks, internal links and backlinks get split across versions, and crawl budget goes on copies instead of new pages. Reused boilerplate, short product descriptions and a templated legal page are not what this is about.

Where the copies actually come from

URL variants. http and https, www and the apex, trailing slash and no trailing slash, uppercase and lowercase paths.
Query parameters. Tracking parameters, session IDs, sorting and filtering on category pages.
Faceted navigation and pagination. Every filter combination generating an indexable URL is the classic e-commerce version of this.
Staging and alternative domains. A test domain that was never blocked, or an old domain still serving content after a migration.
Syndication and print views. The same article republished elsewhere, or a printer-friendly copy sitting on its own URL.

How to find them

Start with a crawl. Screaming Frog, Sitebulb or any crawler that reports duplicate titles, duplicate meta descriptions and pages sharing a canonical will surface most of it. Then check Search Console: the Pages report flags "Duplicate without user-selected canonical" and "Alternate page with proper canonical tag", which tells you what Google actually chose. A site: search on a distinctive sentence finds the rest. If you want to confirm what is indexed for a specific address, here is how to check if a page is indexed.

Fixing it: the canonical is the lever

Self-referencing canonical on every page. Absolute URL, one per page, matching the version you want indexed.
301 where the duplicate has no reason to exist. Redirect old domains, www to apex or the reverse, and legacy URL patterns.
Consistency across signals. The canonical, the sitemap entry, the internal links and the hreflang references should all point at the same version. A canonical that disagrees with the sitemap is a suggestion search engines are free to ignore.
noindex only for pages that must exist but must not rank. Internal search results, thin filter combinations.

The part everyone forgets

The canonical is a one-line tag in the head, which makes it the easiest thing on the page for a deploy to break. A template refactor drops it, a plugin update makes it relative, a section starts shipping two of them, a staging build points every canonical at the staging domain. None of this is visible in the browser and none of it triggers a ticket, which is why a canonical audit has a shelf life of about one release. Our guide to website code change monitoring covers the wider pattern.

How Deltio does it

Deltio does not compare the text of two pages, so it will not tell you that two articles are 80% similar: for that you need a crawler or a similarity tool. What it does is watch the tag that decides the outcome. The SEO scanner checks the canonical on every URL and reports it missing, invalid or present more than once, and it compares consecutive scans, so a canonical that changes value gets flagged as a change rather than sitting there looking normal. The same scan covers title, meta description, H1, lang and hreflang, which is where duplicate-looking pages usually show up first as duplicate titles. Sitemap snapshots run daily and show URLs added or removed, useful when a filter starts generating addresses. Alerts go to email and Slack. See the canonical tag checker for how the check works on a single page.

Keep the fix in place

Fixing duplicates is a project. Keeping them fixed is monitoring. Add the site, set the canonical alerts, and the next time a release rewrites them you will know the same day instead of at the next audit. The 14-day free trial is enough to see the first scan compare.

Frequently asked questions

Does duplicate content cause a Google penalty?: No. Search engines consolidate rather than penalise: they index one URL, drop the others from results and merge the signals onto the chosen version. The damage is losing control of which URL ranks and splitting internal links and backlinks across copies.
What is the fastest way to check a site for duplicate content?: Crawl the site and look at duplicate titles, duplicate meta descriptions and pages sharing a canonical. Then compare that with the Pages report in Search Console, which shows which URL Google actually selected as canonical.
When should I use a canonical and when a 301 redirect?: Use a 301 when the duplicate URL has no reason to exist, for example an old domain or a www variant. Use a canonical when both URLs need to stay reachable, for example a filtered or parameterised version of a category page.
Does Deltio compare page text to find duplicates?: No. Deltio does not do content similarity comparison. It checks the canonical tag on every URL and reports it missing, invalid or duplicated, and it flags when the value changes between two scans, which is what usually breaks after a deploy.
Will Deltio alert me if a canonical tag changes?: Yes. The SEO scanner compares consecutive scans, so a canonical that changes, disappears or starts appearing twice is reported as a change. Alerts arrive by email and Slack, in your language.
How much does Deltio cost?: Starter is £24 a month, or £20 a month billed annually. Professional is £49 a month and Enterprise is £119 a month. All plans include a 14-day free trial.