🔁 Duplicate Sentence Finder

Find sentences that appear more than once in a passage — handy for catching copy-paste repeats in long documents.

Text

Ignore case

How the text is cut into sentences

A sentence is a run of characters up to and including the next full stop, question mark or exclamation mark. A final fragment with no terminator counts too, so nothing is lost from an unfinished paragraph:

/[^.!?]+[.!?]+ | [^.!?]+$/g

The sample text holds four sentences, of which "This is a sample sentence." appears twice and is reported with an x2 badge. Line breaks do not end a sentence - only the three terminators do - so a heading with no full stop is joined onto the paragraph that follows it.

What counts as the same sentence

Runs of whitespace are flattened before comparing. Two copies that differ only by a line break, a double space or indentation still count as duplicates.
Ignore case is on by default, so "The deadline is Friday." matches "The deadline is friday." Untick it to demand a character-for-character match.
Terminating punctuation is part of the sentence. "Ready." and "Ready?" are two different sentences, and so are "Ready." and "Ready...".
The first copy is the one displayed, with a multiplier showing how many times it occurred. The Repeated Sentences figure counts distinct sentences, so one sentence appearing three times adds 1 to it, not 3.

There is no list of abbreviations, so any full stop splits. "Dr. Chen agreed." is read as two sentences, and so is a decimal like 3.14. It rarely changes which duplicates are found, but it does inflate the sentence total.

Frequently asked questions

How do I find repeated sentences in a long document?

Paste the whole document into the box. Any sentence that occurs more than once is listed with a count beside it, and the summary gives the total number of sentences alongside how many of them repeat.

Does it catch sentences that are nearly the same?

No. Matching is exact once case and spacing are normalised, so one extra word, a different tense or a comma moved will read as two separate sentences. It finds copy-paste repeats, not paraphrases.

Why does it say there are more sentences than I wrote?

Every full stop ends a sentence, including the ones in abbreviations, initials and decimal numbers. A paragraph mentioning e.g. Mr. Patel and 1.5 million will be counted as several sentences more than it reads as.