How does it detect sentence boundaries?

It splits on a period, exclamation point, or question mark that's followed by whitespace or the end of the text, keeping the punctuation attached to the sentence it ends.

Does it duplicate words within a sentence too?

No. Only whole sentences are duplicated; the words and punctuation inside each sentence are copied through exactly as written.

What if my text has no sentence-ending punctuation?

The whole input is treated as a single sentence in that case, and duplicating one sentence simply produces the text followed by a repeated copy of itself.

Sentence Duplicator Online - Duplicate Every Sentence

Overview

Introduction

Duplicating every sentence in a passage is a quick way to double its length for a test, add emphasis to a piece of writing, or generate padded sample content.

This tool runs entirely client-side, so nothing you paste is ever uploaded to a server.

What Is Sentence Duplicator?

A sentence duplicator that splits text into sentences on `.`, `!`, or `?` followed by whitespace or the end of the text, then inserts a duplicate copy of each sentence immediately after the original.

It works at the sentence level, unlike a word duplicator, so entire sentences repeat rather than individual words.

How Sentence Duplicator Works

The tool matches sentence-ending punctuation followed by whitespace or end-of-string to split the input into an array of trimmed sentences.

It then builds a new sequence where each sentence is immediately followed by a second copy of itself, and joins everything back together with single spaces.

When To Use Sentence Duplicator

Use it to double the length of sample text for a layout or performance test, add rhetorical repetition to a piece of writing, or generate padded content quickly.

It's a fast way to get the answer without opening a code editor, a REPL, or writing a one-off script just to check.

Often used alongside Sentence Order Reverser, Sentence Remover and Word Duplicator.

Features

Advantages

Keeps each sentence's own wording and punctuation intact.
Works on the sentence level rather than duplicating individual words out of context.

Limitations

Sentence detection relies on `.`, `!`, and `?`; abbreviations like "Dr." or decimal numbers can be misread as sentence boundaries.
Original spacing between sentences isn't preserved; sentences are rejoined with single spaces.

Examples

Duplicating every sentence

Input

This is one sentence. This is another!

Output

This is one sentence. This is one sentence. This is another! This is another!

Each sentence is immediately followed by a duplicate copy of itself.

Best Practices & Notes

Best Practices

Check text with abbreviations or decimal numbers afterward, since the sentence splitter may misread them as boundaries.
Pair with a sentence remover if you only want to duplicate part of a longer passage.

Developer Notes

Sentences are matched with `/[^.!?]*[.!?]+(?=\s|$)|[^.!?]+$/g`, then each match is duplicated with `sentences.flatMap((s) => [s, s])` before being rejoined with single spaces.

Sentence Duplicator Use Cases

Doubling the length of sample text for a layout or performance test
Adding rhetorical repetition to a piece of writing
Generating padded sample content quickly

Common Mistakes

Assuming abbreviations like "Mr." won't be treated as sentence endings; the simple punctuation-based splitter can misread them.
Expecting original inter-sentence spacing to be preserved exactly.

Tips

Combine with a sentence remover tool if you want to duplicate some sentences and delete others in the same workflow.

Sentence Duplicator