Overview
Introduction
Finding which letters appear only once in a word or passage comes up in word games, cipher puzzles, and quick checks for isograms, but counting by eye gets error-prone past a handful of characters.
It runs entirely client-side, so nothing you paste is ever uploaded to a server.
What Is Unique Letter Finder?
A scanner that lists every letter appearing exactly one time anywhere in your text, matched case-insensitively and ordered by first appearance.
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 Unique 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 exactly one before displaying the result.
When To Use Unique Letter Finder
Use it to check whether a word is an isogram, to find rare letters in a passage for a word puzzle, or to spot-check anagram and cipher inputs.
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 Duplicate Letter Finder and String Length Counter.
Features
Advantages
- Case-insensitive matching avoids miscounting the same letter as two different ones.
- Results ordered by first appearance, not alphabetically, matching how the letters actually occur in the text.
- Counts across the entire input, so a letter appearing once in each of several words is correctly excluded rather than reported as unique.
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 Duplicate Letter Finder to see the full picture: which letters repeat and which don't.
- Work one word at a time for puzzle use, since counting across a whole sentence merges the letters of every word together.
- Remember that only letters are considered, so digits and punctuation never appear however rarely they occur.
Developer Notes
Counting uses a `Map<string, number>` built in a single pass over `[...input]`-style iteration with a companion `order` array that records first-appearance sequence, since `Map` insertion order alone isn't reset when a letter's count later exceeds one.
Unique Letter Finder Use Cases
- Checking whether a word or phrase is an isogram-like string
- Finding rare letters in a passage for a word game
- Sanity-checking anagram or cipher tool inputs
Common Mistakes
- Expecting digits or punctuation to be included in the results; only letters are considered.
- Assuming the output is alphabetically sorted when it's actually ordered by first appearance.
Tips
- Use this alongside Duplicate Letter Finder to fully characterize a word's letter composition.
- An empty result means every letter repeats somewhere in the text, which is itself a useful answer when working through a puzzle.