Palindrome Checker

A palindrome reads the same forwards and backwards, but almost every interesting case depends on what you agree to ignore. "Racecar" is symmetric on its raw characters. "A man, a plan, a canal: Panama" is only a palindrome once you strip spaces, punctuation, and capitalisation — and that normalisation step, not the reversal, is where the real work happens.

This tool compares the text against its reverse after removing non-alphanumeric characters and lowercasing, which is the convention nearly everyone means by the word. That handles phrase palindromes correctly, and it is also the exact rule set used by the classic programming exercise, so results here match what a standard implementation would return. Numbers are included in the comparison, so 12321 registers as a palindrome and 2024 does not.

Worth knowing about the edge cases. Emoji and accented characters may or may not survive normalisation depending on how they are encoded, since a single visible character can be stored as several code points. Semordnilaps — words that form a different word when reversed, like stressed and desserts — are not palindromes and will correctly fail. And a single character is trivially a palindrome, which is technically right but rarely what someone is checking for.