About the Palindrome Checker
This palindrome checker tells you instantly whether a word, phrase, sentence or number reads the same forwards and backwards. Paste anything — "racecar", "A man, a plan, a canal: Panama" or 12321 — and it shows the cleaned-up text, its reverse, and how close it comes to being a perfect palindrome.
It is handy for word-game fans and puzzle writers, teachers building wordplay lessons, students checking a programming exercise, and anyone who wants to know whether a date or licence plate is symmetrical. It also finds the longest palindrome hidden inside your text and lists any palindromic words, which helps when you are hunting for wordplay.
By default the check follows the usual convention for phrase palindromes: capital letters, spaces, punctuation and accents are ignored and only letters and digits are compared. Switch to strict mode to compare every character exactly, or to word mode to test whether the order of the words is symmetrical.
How to use the palindrome checker
- 1Type or paste a word, phrase, sentence or number.
- 2Keep the default mode to ignore spaces, punctuation and capitals, or pick strict or word mode.
- 3Read the yes/no verdict and compare the cleaned text with its reverse.
- 4Check the pair table to see exactly where a near-palindrome breaks.
Formula and method
The text is first normalised according to the mode. In the default mode accents are stripped (é becomes e), everything is lowercased and only letters and digits are kept. Strict mode keeps every character, including spaces, punctuation and capitals. Word mode splits the text into words and compares whole words instead of letters.
The checker then compares the first item with the last, the second with the second-to-last, and so on up to the middle; a middle character in an odd-length string has no partner and always matches. The match percentage is the share of these mirrored pairs that agree. The longest palindrome inside the text is found by expanding outward from every possible centre.
- s
- Normalised sequence of characters (or words)
- n
- Length of the sequence
- i
- Position from the start, beginning at 0
Worked examples
A famous sentence palindrome
Removing spaces, commas, the colon and capitals leaves "amanaplanacanalpanama", 21 letters. All 10 mirrored pairs match (the middle "c" stands alone), so the whole sentence is a palindrome.
A word that is not a palindrome
"hello" reversed is "olleh". Neither mirrored pair matches (h/o and e/l), so the match is 0%. The longest palindrome inside the word is the double "ll".
Strict mode catches capital letters
In strict mode "R" and "r" are different characters, so the first pair fails while the other two pairs (a/a and c/c) match: 2 of 3 = 66.7%. The longest exact palindrome is "aceca".
Word-order palindrome
Read word by word, the five words come back in the same order when reversed (fall, leaves, after, leaves, fall), even though the letters themselves do not form a palindrome.
Counting palindromic words in a sentence
The sentence as a whole is not symmetrical, but five of its words are palindromes of three letters or more: wow, racecar, did, level and noon.
Frequently asked questions
What is a palindrome?+
A palindrome is a word, phrase, number or other sequence that reads the same backwards as forwards, such as "level", "racecar", "noon" or 12321. Phrase palindromes usually ignore spaces, punctuation and capital letters.
What is the longest palindrome word in English?+
Among dictionary words, "tattarrattat" (12 letters, coined by James Joyce in Ulysses) is often cited; common words include "redivider" (9 letters) and "racecar" (7). The Finnish "saippuakivikauppias" (19 letters) is a famous non-English example.
Are numbers palindromes too?+
Yes. A palindromic number reads the same in both directions, such as 121, 1331 or 12321. Dates can be palindromes as well — for example 02/02/2020 written as 02022020.
Does punctuation count in a palindrome?+
Conventionally no. Sentence palindromes like "Was it a car or a cat I saw?" only work when spaces, punctuation and capitals are ignored. Use strict mode if you need an exact character-for-character mirror.
What is a word-unit palindrome?+
A word-unit palindrome reads the same when the order of words is reversed, such as "Fall leaves after leaves fall". The letters need not be symmetrical — only the sequence of words.