Duplicate Content Comparer
Compare two pages and see exactly which passages they share.
What you provide
How this calculation works
Both texts are broken into overlapping five-word sequences, and the comparison counts how many sequences appear in both. That approach catches reworded passages that a straight character comparison would miss, and it ignores the order things appear in, so a page with the same sections rearranged still scores as similar. Adjacent matching sequences are then stitched back together so you get readable passages rather than a list of fragments.
What the results mean
- Similarity
- Shared five-word sequences as a share of all sequences across both texts. Above 40% means substantial shared phrasing rather than coincidental overlap.
- First text found in second
- How much of the first document also appears in the second. High here with low overall similarity means the first is largely contained inside a longer second document.
- Matching passages
- The longest runs of identical phrasing, in order of length. This is where to look first, since it shows what to rewrite or consolidate.
Common problems and fixes
- Two product pages score high and both need to exist
- This is the standard case for a canonical tag. Pick the version that should be indexed and have the other point at it, which consolidates the signals rather than splitting them. If both genuinely serve different searches, the fix is to make them genuinely different, usually by writing about what distinguishes the products rather than repeating the shared specification.
- The score is high but only because of navigation and footer text
- Paste the main content of each page rather than the full markup. Site-wide boilerplate repeats everywhere by design, and including it inflates every comparison. If you are working from HTML, copy the main content region from the browser inspector.
Frequently asked questions
Is there a duplicate content penalty?
No, and this is one of the most persistent myths in SEO. What actually happens is that search engines cluster near-identical pages and show one, so the others stop earning traffic. That is a real problem when they pick the version you did not want, but it is a selection, not a punishment. Deliberate large-scale copying of other sites is a separate matter and is treated as spam.
How much overlap is acceptable?
There is no threshold. Some duplication across a site is unavoidable and expected: legal text, shipping information, specification tables. What matters is whether two pages compete for the same searches with nearly the same words, in which case one of them is not earning its place.
Can this find sites that have copied my content?
No. It compares two texts you provide and never leaves your browser. To find copies elsewhere, search for a distinctive sentence from your page in quotation marks, which finds most straightforward copying quickly.
Put this on your own site
Free to embed, no attribution required beyond the source link the frame carries itself. It runs entirely in your visitor's browser, sets no cookies and loads no third-party script.
<iframe src="https://runthetests.com/embed/duplicate-content-checker/" width="100%" height="560" style="border:1px solid #e5e5e5;border-radius:8px" title="Duplicate Content Comparer" loading="lazy"></iframe>
Preview it at https://runthetests.com/embed/duplicate-content-checker/. Embedded pages are marked noindex, so yours stays the canonical copy — not this one.