Palindrome Checker

What this tool is used for

• Checking whether a word or a phrase reads the same both ways.
• Verifying a puzzle answer before committing to it as the solution.
• Testing an implementation against a known case.
• Checking a phrase ignoring spaces and punctuation.
• Exploring candidates for a wordplay exercise.

Frequently Asked Questions

What normalisation happens before checking?

Case is folded and punctuation and spaces are stripped, because 'A man, a plan, a canal: Panama' is a palindrome only after that. A raw character-by-character comparison would reject nearly every real example.

Should accents be stripped too?

That is a genuine judgement call. Unicode NFD decomposition separates a letter from its accent, so you can compare base letters only — but for languages where é and e are distinct letters, folding them is arguably wrong.

What is a word-level palindrome?

One where the WORDS read the same in reverse rather than the letters: 'You can cage a swallow, can't you?' fails at letter level but works at word level. They are a different category and need a different check.

Does reversal work correctly with emoji?

Only if it operates on grapheme clusters. Reversing by code unit splits emoji surrogate pairs into invalid halves and detaches combining accents, so a naive checker can crash or give nonsense on non-ASCII input.

What is the longest palindrome in English?

'Tattarrattat', coined by Joyce in Ulysses for a knock at the door, at 12 letters; 'detartrated' is the longest in most dictionaries at 11. Sentence-level palindromes have no meaningful upper bound.

Should numbers and mixed content be checked the same way?

Digits reverse cleanly, so numeric palindromes are simpler than textual ones. What varies is whether punctuation and spaces are ignored — a rule that must be stated, since `A man, a plan` is a palindrome only under the loose reading.

Are there palindromes in other scripts?

Yes, and they raise a question Latin does not: whether the unit is the code point, the grapheme, or the syllable. In an abugida such as Devanagari the three give different answers for the same string.

Common errors and gotchas

• Comparing with punctuation and spaces included, which fails most phrase palindromes.
• Comparing case-sensitively, which fails any capitalised palindrome.
• Reversing by code unit, which mishandles accented characters and emoji.
• Assuming a numeric palindrome check is the same operation, where leading zeros matter.
• Overlooking that some languages' palindromes depend on collation rather than code points.