Duplicate content means the same or near-identical page is reachable at more than one address. It is rarely a penalty. The usual cost is confusion: Google picks one version and ignores the rest, and it may not pick the one you wanted. A canonical tag or a 301 redirect tells Google which version to keep.
Duplicate content means the same, or almost the same, content can be reached at more than one web address. It is rarely a penalty. The usual damage is confusion: Google picks one version to show, may ignore the rest, and may not choose the one you wanted. Canonical tags and 301 redirects are how you tell Google which version counts.
How duplicates sneak onto a normal site
Most owners never copy a page on purpose. Duplicates appear by accident:
- www and non-www. The same page loads at both versions of your address.
- http and https. An old unsecured version still works alongside the secure one.
- Trailing slashes. A page loads with and without a slash on the end.
- .html and non-.html versions. Common on sites that were rebuilt or migrated.
- URL parameters. Tracking tags, sort options and filters create endless variations of one page.
- Near-identical service pages. A builder has one page per suburb, and the only change is the suburb name.
- Copied descriptions. Shop product text lifted word for word from a supplier or manufacturer.
Each of these is a different address to Google, even if it looks like one page to you. On a larger site, finding every one of them is a typical part of a technical SEO audit.
Why it matters, and why it is not a panic
Google has said that duplicate content on a site is not grounds for action unless it appears to be created to deceive. So for a Christchurch tradie, the risk is not a penalty. It is dilution. Links and signals get split between versions, Google may show an address you would rather it did not, and pages that add nothing new get left out of the index.
Say a Papanui electrician has separate pages for Papanui, Merivale and Burnside, each with the same four paragraphs and the suburb swapped. Google sees three pages saying one thing. It may index one, drop the others, or show whichever it likes. The fix is not clever tagging. It is either to write each page with real differences, such as the types of jobs done there and local details, or to merge them into one stronger page covering all three suburbs.
Canonical tag or 301 redirect: which one?
A 301 redirect sends everyone, visitors and Google, from one address to another permanently. Use it when a duplicate should not exist at all: the http version redirecting to https, the www version to non-www (or the reverse, whichever you chose), or an old address to its replacement.
A canonical tag sits in the page code and says "this is the preferred version of this page". Visitors can still reach the other address. Use it when both versions legitimately need to exist, such as a product page reachable with different filter parameters, or a printable version of an article.
A good habit is for every indexable page to carry a canonical tag pointing to itself. It tells Google plainly which address is the official one. Remember that a canonical is a hint, not a command. Google can choose a different version if other signals disagree, for instance if your internal links and sitemap point to another address. Keep those signals consistent. Your sitemap should list only the preferred addresses, and a canonical pointing at a page that redirects elsewhere confuses things further.
How to spot duplicates yourself
- Try the variations. Type your address with and without www, with http, and with a trailing slash. Each should end up at one version through a redirect. If two load separately, you have duplicates.
- Use a site search. Type site: followed by your domain into Google, then look for repeated titles or odd addresses with question marks in them.
- Check Search Console. In the Pages report, look for the statuses "Duplicate without user-selected canonical" (Google found copies and you did not say which you prefer) and "Duplicate, Google chose different canonical than user" (you named a favourite and Google disagreed). Inspect a flagged address to see which version Google picked.
- Read your own pages. If two pages could swap titles without anyone noticing, one of them is probably redundant.
Duplicates also come back after a site move, so they feature in any redesign plan, and they sit near the top of most technical SEO checklists. If you are weighing up domains as well, choosing between .co.nz and .com matters here, because owning both without a redirect creates a duplicate site.
Common mistakes
Canonical-tagging everything to the homepage. Pointing all pages at one address tells Google the others do not matter, and they may drop out.
Blocking duplicates in robots.txt. Google then cannot see the canonical tag. Use a redirect or canonical instead.
Using noindex as a shortcut. It removes the page from results but does not tell Google which version you want kept.
Ignoring the content. Tags fix address problems, not thin pages. If the content is the same, change the content.
Cleaning this up will not lift your rankings by itself. It stops them leaking, which makes everything else you do count properly.
Not sure which of your pages are competing with each other? An SEO audit maps every duplicate and tells you whether to redirect, tag or rewrite, and a free SEO audit is a good first look.
