What does the N parameter control?

N sets how often a letter gets duplicated: N=1 (the default) duplicates every letter, N=2 duplicates every second letter, and so on, counting only letters, not spaces or punctuation.

Does it duplicate spaces or punctuation?

No, only letters are counted and duplicated. Spaces, digits, and punctuation pass through unchanged.

Is the duplication case-sensitive?

The duplicate always matches the case of the original letter, since the tool simply repeats the exact character it found.

Letter Duplicator Online - Double Every Letter in Text

Overview

Introduction

Doubling letters by hand is tedious and error-prone, especially across a long passage, but a small script can do it instantly and consistently.

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

What Is Letter Duplicator?

A letter duplicator that inserts a copy of each letter directly after itself, or after every Nth letter if you only want a partial effect.

It runs entirely client-side as part of this site's String Tools collection, so nothing you paste is ever uploaded to a server.

How Letter Duplicator Works

The tool walks through the input character by character, counting only letters, and appends an extra copy of a letter whenever the running letter count is a multiple of N.

Non-letter characters like spaces, digits, and punctuation are copied through untouched and don't affect the counting.

When To Use Letter Duplicator

Use it to create a stylized 'stuttering' or emphasis effect in text, or to stress-test a UI or font with doubled characters.

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 String Repeater and Letter Remover.

Features

Advantages

Configurable frequency via N, not just an all-or-nothing duplication.
Preserves the case of every duplicated letter automatically.
Counts letters separately from everything else, so spaces and punctuation never shift the duplication cadence partway through a phrase.

Limitations

Only letters are duplicated; digits and symbols are never doubled.
Matches the English alphabet only, so accented and non-Latin letters are neither doubled nor counted towards N.

Examples

Duplicating every letter

Input

cat

Output

ccaatt

With N=1, each of the three letters is immediately followed by a copy of itself.

Duplicating every second letter

Input

hello

Output

hellllo

With N=2, only the 2nd and 4th letters ('e' and 'l') are duplicated.

Best Practices & Notes

Best Practices

Use N=1 for a strong stylistic effect, or a higher N for a subtler variation.
Keep the input short when using N=1, since doubling every letter makes longer passages genuinely hard to read.
Check the result where it will actually be used, because doubled letters defeat spell-checking and are read out literally by screen readers.

Developer Notes

The implementation tracks a separate `letterIndex` counter incremented only when `/[a-zA-Z]/` matches the current character, so N counts letters exclusively and non-letter runs never shift the duplication cadence.

Letter Duplicator Use Cases

Creating stylized or 'stuttering' text for creative writing
Stress-testing a font or text layout with doubled characters
Generating quick test strings with a predictable letter pattern

Common Mistakes

Expecting spaces or punctuation to be duplicated along with letters.
Setting N to 0, which isn't a valid frequency.

Tips

Combine with a monospace font to see the doubling effect most clearly.
A higher N produces a more natural-looking irregular stutter, because the doubled letters land at different points within each word.

Letter Duplicator