Palindrome Checker and Builder
TextEverything runs locally in your browser — nothing is uploaded
“A man, a plan, a canal: Panama” is a palindrome once you ignore case, punctuation and spaces. The three “ignore” switches are explicit rather than assumed — all on by default, which matches how people read a sentence. Judging is done by code point, not UTF-16 unit, so emoji and combining characters are never split. If a line is not a palindrome you can complete it both ways: `abc` becomes `abcba` (append, using the longest palindromic suffix) or `cbabc` (prepend, using the longest palindromic prefix) — always the shortest completion. You can also list the longest palindromic substring. Everything runs in your browser: nothing is uploaded, no request is made, and it works offline.
Features
- One word or sentence per line, each with a yes/no verdict
- Ignore case, punctuation (Latin, CJK and full-width) and whitespace independently
- Complete both ways: append (abc → abcba) and prepend (abc → cbabc)
- Shortest completion, based on the longest palindromic suffix or prefix
- Optional longest palindromic substring with its length
- Code-point based, so emoji and combining marks stay intact
- Each line is its own block — copy one row or all of them
How to use
- Paste the text to check, one item per line
- Toggle the ignore-case, punctuation and whitespace switches as needed
- Turn on completion or the longest-substring option
- Each line becomes a block; use the row copy button to take one
FAQ
- Why are all the “ignore” switches on by default?
- Because people do not count case or punctuation when reading a sentence — “A man, a plan” feels like a palindrome. Turn all three off to compare character by character.
- Can emoji break the check?
- No. Judging is by Unicode code point, so an emoji counts as one character. Comparing UTF-16 units would split a surrogate pair in half, which is exactly what this avoids.
- Why two completion directions?
- `abc` can become `abcba` or `cbabc`, depending on whether you want the original on the left or the right, so both are offered. The algorithm always returns the shortest completion.
- Is anything uploaded?
- No. It is all computed in memory in your browser, no request is made, and it works offline.
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