Palindrome Checker

Type a phrase and this tool tells you right away whether it's a palindrome, text that reads the same forwards and backwards, which every checker on the web manages. What almost none of them do is show you the reason. When the answer is no, this one points at the exact place the mirror falls apart, and it lines up the cleaned text beside its reverse in color so you can see which characters matched and which one broke it. It runs in your browser, updates as you type, and nothing you paste is ever uploaded.

It also handles two different kinds of palindrome. The usual kind works on letters, so "racecar" and "A man, a plan, a canal: Panama" both come back green. The second works on whole words, a rarer puzzle most checkers cannot do at all. Switch the mode to Words and "King, are you glad you are king?" reads the same word for word in reverse, even though the letters are a jumble. You choose which question you are asking with one toggle.

1. Type or paste your text into the box. A word, a sentence, a phone number, whatever you have. The verdict appears the moment you stop typing.
2. Pick how to check. Leave it on Letters for the normal palindrome. Switch to Words to test whether the word order reads the same in reverse.
3. Read the color-coded comparison. The left box shows the text as the tool actually compared it, the right box shows that same text reversed. Green means a character or word lined up with its mirror partner, red marks the ones that did not.
4. When it says no, read the line below the verdict. It tells you how far the mirror held and the exact pair that broke it, so you are not left scanning the whole string yourself.
5. Adjust the two matching options for a stricter test. Turn off Ignore case to make "R" and "r" count as different letters. Turn off Ignore spaces and punctuation to demand a literal, character for character match.
6. Tap an example to load a known palindrome, and one that is not. The word-order example flips the mode for you so you can watch that feature in action.
7. Copy the result to keep it, or use Share to send a link that reopens your exact text and settings on someone else's screen.

A short word you can verify with your eyes. "level" is obvious, so is "hello". The trouble starts the moment a phrase gets long. Counting inward from both ends of a twenty-word sentence palindrome, you lose your place, and one letter out of position hands you a confident wrong answer. That is the moment a bare yes or no stops being any help.

So the comparison here is built to make the break visible. Every character is colored by whether it agrees with its partner on the far side, and when something disagrees the reversed box shows a run of green with a single red character sitting right where the two sides parted ways. Underneath, a plain sentence says what happened, something close to "the first nine letters mirror correctly, then 'r' meets 't' and the match stops". You go fix that one spot instead of rereading the whole phrase and hoping.

This helps most when you wrote the palindrome yourself and it came out almost right, which is the hardest case to catch by eye and the one a plain checker helps with least.

Most people picture a palindrome as a letter game, flip the letters and see if they match. There is a second kind though, and it is the reason for the Words mode. A word-level palindrome reads the same when you reverse the order of the whole words, even though the individual letters come out scrambled. "King, are you glad you are king?" is the classic. Read the words backwards and you get king, are, you, glad, you, are, king, the same list, even though those letters mirror nowhere.

These are a genuinely different puzzle, and harder to write because you are limited by real words rather than single letters. The same two matching options still apply. With Ignore case and punctuation on, "king?" and "king" count as the same word and the phrase passes. Turn them off and that trailing question mark makes the two ends disagree.

There are two honest ways to check a palindrome and they can disagree on the same input. The default here is the everyday one. It strips out anything that is not a letter or a number, treats upper and lower case as equal, then compares what is left. That is why a messy sentence like "Was it a car or a cat I saw?" comes back as a palindrome, because underneath the spaces and the question mark it is perfectly symmetric.

The strict check keeps everything. Every space, every comma, and the gap between a capital and a small letter all count. Under that rule "racecar" still passes, but "Racecar" fails, because the capital R at the start lands on a lowercase r at the end once you flip it. Both answers are defensible, and which you want depends on the job. A poet playing with sentence palindromes wants the everyday check. A coding test that has to reject "Racecar" on its capital needs the strict one.

Palindromes are not only a letter thing. The tool keeps digits when it cleans the input, so you can paste a number straight in. 12321 and 9009 come back green, and so does a phone number that happens to mirror. Dates work once you drop the slashes, so 02/02/2020 passes with the defaults. Anything made of letters and numbers is fair game.

"Check if a string is a palindrome" is a staple interview warm-up, usually with the twist to ignore case and skip non-letter characters. That is the same everyday-versus-strict split the toggles expose. Match the options to the problem, type an input, and you have the expected output to test your own function against, including the edge cases people forget, a single character, an empty string, or all punctuation.