What exactly counts as a palindrome?

A palindrome is a string that reads the same forwards and backwards. With the default rules (ignore case, ignore spaces and punctuation) words like racecar, level and noon pass, and so do phrases like Was it a car or a cat I saw. Single characters count as palindromes. Empty or whitespace-only input does not, because there is nothing to mirror.

Does "A man, a plan, a canal: Panama" count?

Yes, with the default rules. The tool first strips spaces, commas and the colon and lowercases everything, leaving amanaplanacanalpanama, which is symmetric. Turn off ignore spaces and punctuation and the same phrase fails, because the raw characters with their commas and capital letters no longer mirror. That toggle lets you check strict character equality when you need it.

Can it handle Chinese palindromes?

Yes. Comparison runs by Unicode code point, not byte, so each Han character is treated as one unit. The classic 上海自来水来自海上 (Shanghai tap water comes from the sea) reads the same in both directions and is reported as a palindrome. 上海的水 is not. Japanese, Korean, Arabic and accented Latin text are all judged the same correct way.

What is the longest palindrome substring it finds?

It is the longest run of characters inside your text that is itself a palindrome, returned as a real slice and highlighted. For babad it returns bab (the leftmost match when bab and aba tie on length); for cbbd it returns bb; for xracecary it returns racecar. This finder is case and punctuation sensitive on purpose so the highlight lines up with what you typed.

Does it care about uppercase and lowercase?

By default no, so Racecar and racecar both pass. Untick ignore case to make the check strict: then Racecar fails, because the capital R at the front does not equal the lowercase r at the end. Use the strict mode when case actually matters, for example validating an exact token rather than reading a phrase out loud.

Is my text sent anywhere?

No. Every step (cleaning, the mirror comparison and the longest-substring search) is plain JavaScript that runs in your browser tab. The one thing to know: the shareable link puts your text in the URL so a friend opening it sees the same input, which means a pasted share link will appear in the recipient server log. For something private, use the copy button instead of sharing the URL.

Practice the classic coding-interview question

Longest palindromic substring is a staple whiteboard problem. Paste a test string like babad or cbbd, read off the expected answer (bab and bb), and verify your own expand-around-center or DP solution against it. The highlight shows exactly which slice the tool picked and which end the tie broke toward, so when your code returns aba instead of bab you can see it is a leftmost-tie convention, not a bug.

Settle a word-game or crossword argument

Someone claims their phrase is a palindrome. Drop it in with ignore spaces and punctuation on, and the verdict is instant: Was it a car or a cat I saw passes, Almost a palindrome does not. For Scrabble and word-ladder players, the longest-palindrome finder also surfaces the best symmetric run buried in a long messy string.

Check a Chinese or bilingual palindrome

Chinese has a rich tradition of palindrome couplets. Paste 上海自来水来自海上 or 客上天然居居然天上客 and the tool confirms the symmetry by code point, which a naive byte check would get wrong. Mixed scripts work too, so a line that blends Latin and Han is judged the same correct way without you reformatting anything.

Validate test fixtures or generated strings

Building a palindrome generator, a data-cleaning script or a teaching demo? Paste a batch into per-line mode and every line gets a pass or fail tick at once, so you can eyeball a hundred fixtures in seconds rather than running them through a REPL one at a time. Copy the result straight into a bug report or a lesson handout.

Palindrome Checker and Longest Palindrome Finder

Tells you if text reads the same backwards, finds the longest palindrome inside, handles Chinese and emoji, runs in your browser

Runs locally
Category Text
Best for Removing repetitive cleanup work from everyday writing and operations.

Paste a word, phrase or several lines. The tool says whether it reads the same forwards and backwards, and finds the longest palindrome hiding inside. Comparison runs by Unicode code point, so accents, emoji and Chinese stay whole. Everything happens in your browser; nothing is uploaded.

Comparison rules

Ignore caseIgnore spaces and punctuationCheck each line separately

Your text

Verdict

Type something to check.

What this tool does

A free palindrome checker that tells you whether a word, phrase or whole line reads the same forwards and backwards, then finds the longest palindromic substring hiding inside it. Toggle two rules: ignore case and ignore spaces and punctuation. Both are on by default, which is why "A man, a plan, a canal: Panama" comes back as a palindrome even though the raw string clearly is not symmetric character for character. Comparison runs by Unicode code point, so accents stay attached, emoji never get torn in half, and Chinese palindromes such as "上海自来水来自海上" are judged correctly instead of byte by byte. The longest-palindrome finder uses expand-around -center and highlights the match in place, which is handy for coding interviews and word puzzles alike. Turn on per-line mode to check a whole list at once. One click copies the result, and the shareable URL reopens your exact text and settings. 100% client-side, nothing is uploaded.

Tool details

Input: Text; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Text · Student; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Palindrome Checker fits into your work

Use it to clean, compare, reshape, or extract plain text before it goes into a document, CMS, spreadsheet, or prompt.

Text jobs

Removing repetitive cleanup work from everyday writing and operations.
Making text easier to compare, paste, publish, or feed into another tool.
Working with content locally when the text is private or unfinished.

Text checks

Scan for unintended whitespace, duplicate lines, and lost punctuation.
For long text, test the first few lines before applying the whole change.
Copy the final output only after checking the preview.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Practice the classic coding-interview question
Longest palindromic substring is a staple whiteboard problem. Paste a test string like babad or cbbd, read off the expected answer (bab and bb), and verify your own expand-around-center or DP solution against it. The highlight shows exactly which slice the tool picked and which end the tie broke toward, so when your code returns aba instead of bab you can see it is a leftmost-tie convention, not a bug.
Settle a word-game or crossword argument
Someone claims their phrase is a palindrome. Drop it in with ignore spaces and punctuation on, and the verdict is instant: Was it a car or a cat I saw passes, Almost a palindrome does not. For Scrabble and word-ladder players, the longest-palindrome finder also surfaces the best symmetric run buried in a long messy string.
Check a Chinese or bilingual palindrome
Chinese has a rich tradition of palindrome couplets. Paste 上海自来水来自海上 or 客上天然居居然天上客 and the tool confirms the symmetry by code point, which a naive byte check would get wrong. Mixed scripts work too, so a line that blends Latin and Han is judged the same correct way without you reformatting anything.
Validate test fixtures or generated strings
Building a palindrome generator, a data-cleaning script or a teaching demo? Paste a batch into per-line mode and every line gets a pass or fail tick at once, so you can eyeball a hundred fixtures in seconds rather than running them through a REPL one at a time. Copy the result straight into a bug report or a lesson handout.

Common pitfalls

Assuming the empty string is a palindrome. Some textbook definitions call "" trivially palindromic; this tool reports empty and whitespace-only input as NOT a palindrome, because in real use a true verdict there just flatters junk input. A single character, however, does count.
Forgetting that the default rules ignore case and punctuation. If you actually need strict character equality (validating a token, not reading a phrase), untick both options first. Otherwise Racecar, RACECAR and racecar all pass, which is correct for reading aloud but wrong for an exact-match check.
Expecting the longest-palindrome finder to ignore case too. It deliberately works on the raw string so the highlight lines up with what you typed, so AbcbA returns bcb, not AbcbA. The verdict respects your options; the substring finder is always literal.

Privacy

Every step (the cleaning pass, the mirror comparison and the longest -substring search) is plain JavaScript that runs entirely in your browser tab. Your text, the verdict and the highlighted match never leave the page, and nothing about what you typed is logged. The one caveat: the shareable link encodes your text and the two option toggles in the URL query string, so a "share link" pasted into chat will record that text in the recipient server access log. For something you would rather keep private, use the copy button and paste the result instead of the URL.

FAQ

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Palindrome Checker and Longest Palindrome Finder

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Palindrome Checker fits into your work

Text jobs

Text checks

Good next steps

Real-world use cases

Practice the classic coding-interview question

Settle a word-game or crossword argument

Check a Chinese or bilingual palindrome

Validate test fixtures or generated strings

Common pitfalls

Privacy

FAQ

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