Palindromes Explained: Words That Read the Same Backwards

A palindrome is a word, phrase or number that reads the same forwards and backwards. "Level", "radar" and "racecar" are classic examples.

Types of palindromes

• Word palindromes: kayak, refer, madam, rotor.
• Sentence palindromes, which usually ignore spaces, punctuation and capital letters: "A man, a plan, a canal: Panama", "Never odd or even", "Was it a car or a cat I saw?"
• Number palindromes: 121, 1331, 12321.
• Date palindromes: dates such as 12/02/2021 (in day/month/year or month/day/year form) read the same in both directions.
• Word-unit palindromes, where the order of words, not letters, is symmetrical: "Fall leaves after leaves fall."

How to check a palindrome

1. Paste the phrase into the reverse text generator.
2. Compare the input with the Reverse letters output.
3. For sentences, ignore capitals, spaces and punctuation when comparing.

The Reverse word order output is useful for testing word-unit palindromes.

Palindromes in programming

Checking whether a string is a palindrome is a classic coding exercise:

function isPalindrome(text) {
  const clean = text.toLowerCase().replace(/[^a-z0-9]/g, '');
  return clean === [...clean].reverse().join('');
}

Palindromes in nature and science

DNA contains "palindromic sequences", where a strand reads the same as its complementary strand in the opposite direction. These sequences are important in genetics, including as recognition sites for some enzymes.

Try making your own

Start from the middle and build outwards, adding matching letters on both sides. It is harder than it looks, which is exactly why palindromes make great puzzles.

Frequently asked questions

What are some famous palindromes?

Famous palindromes include "A man, a plan, a canal: Panama", "Never odd or even" and "Was it a car or a cat I saw?". Palindrome words include level, radar, kayak and racecar. These palindrome sentences ignore spaces and punctuation.

What are palindrome numbers and palindrome dates?

Palindrome numbers read the same both ways, like 121 or 12321. Palindrome dates do the same, such as 22/02/2022 written in day/month/year format.

Is there a palindrome checker?

Use the reverse text generator as a palindrome checker: compare your text with the "Reverse letters" output. For sentences, ignore spaces, punctuation and capital letters when comparing.

How to write a palindrome program?

A simple palindrome program removes non-letters, lowercases the text, reverses it and compares. Palindrome in JavaScript: clean === [...clean].reverse().join(''). The same idea works in any language.

What words spell other words backwards?

Words that spell other words backwards are called semordnilaps (palindromes spelled backwards): stressed and desserts, live and evil, star and rats. An anagram is different: it rearranges letters in any order.