Palindrome Checker
Check whether a word, sentence, list or number reads the same backwards – and see exactly where it doesn’t, the longest palindrome inside and how to fix it.
- Mirror view
- Text, words, lists, numbers
- Longest palindrome inside
- Runs in your browser
Checked in your browser. Nothing is uploaded.
How to check a palindrome
- Choose what to checkPick Text for words and sentences, Words for word-by-word palindromes, Lines to check a list, or Number.
- Type or pasteThe answer appears as you type. Choose whether to ignore capitals, spaces, punctuation and accents.
- Explore the resultThe mirror view highlights any characters that don’t match. See the longest palindrome inside your text and the fewest changes needed to make one.
Famous palindromes
| Palindrome | Type |
|---|---|
| racecar, level, kayak, rotator, Malayalam | Words |
| A man, a plan, a canal: Panama | Sentence |
| Was it a car or a cat I saw? | Sentence |
| Madam, in Eden, I’m Adam | Sentence |
| Fall leaves after leaves fall | Word-level |
| 12321, 9009, 1234554321 | Numbers |
| 02/02/2020, 22/02/2022 | Dates (DDMMYYYY) |
How palindromes are checked
The text is cleaned according to your options, then the first character is compared with the last, the second with the second-last, and so on towards the middle. If every pair matches, it’s a palindrome. The longest palindrome inside your text is found with Manacher’s algorithm, which scans the text once.
Palindromes in programming
“Is it a palindrome?” is a classic coding interview question. A simple solution reverses the cleaned string and compares; a faster one uses two pointers moving inward. Related problems include the longest palindromic substring and the minimum insertions to form a palindrome – both shown in the results above.
Frequently asked questions
What is a palindrome?
A word, phrase, number or sequence that reads the same forwards and backwards, such as “level”, “racecar” or 12321. For sentences, spaces, punctuation and capital letters are usually ignored – so “A man, a plan, a canal: Panama” counts.
What is a word-level palindrome?
A sentence whose words, not letters, read the same in reverse order – for example “Fall leaves after leaves fall”. Choose the Words mode to check these.
Is 0 or a single letter a palindrome?
Yes. Any single character reads the same both ways, so “a” and 7 are palindromes. Negative numbers like -121 are not, because the minus sign has no partner at the other end.
What does “insertions to fix” mean?
It’s the smallest number of characters you’d need to add anywhere to turn your text into a palindrome. For example, “abc” needs 2 (abcba). “Changes to fix” is how many characters you’d need to replace instead.
What is a Lychrel number?
A number that never becomes a palindrome when you repeatedly reverse its digits and add them to the original. 196 is the most famous candidate – it has been taken to billions of digits without reaching a palindrome, though no one has proved it never will.
Does it work with accents and other languages?
Yes. The checker works with any script and treats emoji and accented letters as single characters. Tick “Ignore accents” so that é matches e.
Can I check a whole list at once?
Yes. Choose Lines, paste one item per line, and every line is marked ✓ or ✗. You can then copy just the palindromes or just the others.
Is my text uploaded?
No. Everything is checked in your browser.
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