Overview
Introduction
Spotting which letters repeat, and how often, comes up in word games, cipher analysis, and typing-pattern checks, but tallying letters by eye gets tedious and error-prone past a short word.
It runs entirely client-side, so nothing you paste is ever uploaded to a server.
What Is Duplicate Letter Finder?
A scanner that lists every letter occurring more than once anywhere in your text, matched case-insensitively, each shown with its total occurrence count.
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 Duplicate Letter Finder Works
The tool walks the text character by character, lowercases each letter, tallies occurrence counts in a map, and records the order letters were first seen.
It then filters that list down to letters whose final count is greater than one and reports each with its count.
When To Use Duplicate Letter Finder
Use it to find the most-repeated letters in a passage, check a word for repeated characters before a puzzle, or verify a generated string's letter distribution.
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 Unique Letter Finder and String Length Counter.
Features
Advantages
- Case-insensitive matching avoids miscounting the same letter as two different ones.
- Shows the exact occurrence count for each repeated letter, not just a yes/no flag.
Limitations
- Only considers alphabetic characters; digits, symbols, and whitespace are ignored entirely.
- Does not distinguish accented letters from their unaccented form.
Examples
Best Practices & Notes
Best Practices
- Pair with Unique Letter Finder to see the full picture: which letters repeat and which don't.
Developer Notes
Counting uses a `Map<string, number>` built in a single pass over the input with a companion `order` array that records first-appearance sequence, then filters to entries with a count greater than one before formatting the `letter: count` report.
Duplicate Letter Finder Use Cases
- Finding the most-repeated letters in a passage
- Checking a word for repeated characters before a puzzle
- Verifying a generated or randomized string's letter distribution
Common Mistakes
- Expecting digits or punctuation to be included in the results; only letters are considered.
- Assuming the output is sorted by count when it's actually ordered by first appearance.
Tips
- Use this alongside Unique Letter Finder to fully characterize a word's letter composition.