Palindrome Checker

Check if a word or phrase reads the same forwards and backwards. Supports batch mode and includes a famous palindromes reference.

Enter a word or phrase above to check if it is a palindrome.

How to Use the Palindrome Checker

  1. Check mode — Type or paste any word or phrase. The tool instantly shows whether it is a palindrome, displays the cleaned and reversed strings, and highlights matching character pairs.
  2. Batch mode — Paste a list of words or phrases (one per line) to check them all at once. Results appear in a table with pass/fail indicators.
  3. Famous Palindromes — Browse a reference list of well-known palindromes organized by type.

What Is a Palindrome?

A palindrome is a word, phrase, number, or sequence that reads the same forwards and backwards when you ignore spacing, punctuation, and capitalization. The term comes from the Greek "palindromos" (πᾰλίνδρομος) meaning "running back again." Single-word palindromes include "racecar," "level," "madam," "civic," "radar," and "rotator." Sentence palindromes — sometimes called semordnilaps or phonetic palindromes — include classics like "A man, a plan, a canal: Panama" and "Was it a car or a cat I saw?"

How Palindrome Detection Works

The algorithm is straightforward: (1) Remove all non-alphanumeric characters from the string, (2) Convert to lowercase, (3) Compare the cleaned string to its reverse. In code, the two-pointer technique is commonly used — starting a pointer at each end and moving them toward the center, comparing characters at each step. If any pair of characters does not match, the string is not a palindrome. The two-pointer approach runs in O(n) time and O(1) space. The sort-based approach requires O(n) space but is equivalent in correctness. This tool uses the reverse-and-compare method for clarity.

Palindromic Numbers

Palindromic numbers read the same in both directions: 121, 1331, 12321, 99, 11. They appear frequently in combinatorics and recreational mathematics. The problem of finding the next palindromic number after a given number is a common coding exercise. Palindromic primes (primes that are also palindromes) include 2, 3, 5, 7, 11, 101, 131, 151, 181, 191.

Palindromes in Computer Science

Palindrome problems are a staple of technical interviews and competitive programming. Common variants include: checking if a linked list is a palindrome (in O(n) time, O(1) space using the fast/slow pointer technique), finding the longest palindromic substring (Manacher's algorithm runs in O(n)), counting palindromic substrings, and generating all partitions of a string where every partition is a palindrome. These problems test understanding of two-pointer techniques, dynamic programming, and string manipulation. Related tools: Anagram Checker, Diff Checker.

Frequently Asked Questions

A palindrome is a word, phrase, number, or sequence that reads the same forwards and backwards. Examples include "racecar", "level", and "A man, a plan, a canal: Panama". Spacing and punctuation are ignored when checking phrases.
The checker strips all non-alphanumeric characters and converts to lowercase. It then compares the cleaned string to its reverse. If they match, the input is a palindrome. Both the cleaned string and reversed form are shown for verification.
Yes. The checker keeps alphanumeric characters (letters and digits) and discards everything else. So "1001" is a palindrome, "1 2 1" is a palindrome, and "A1b1A" (cleaned to "a1b1a") is a palindrome.
Batch mode lets you paste a list of words or phrases (one per line) and checks all of them at once. Results appear in a table with a pass/fail indicator for each entry. Useful for testing large word lists.
Some of the longest palindromes include "A man, a plan, a canal: Panama" and "Was it a car or a cat I saw?". The word "tattarrattat" coined by James Joyce is often cited as the longest palindromic word in the Oxford English Dictionary.