Palindromes and anagrams: the rules, famous examples and how to check

A palindrome reads the same backwards as forwards, like racecar or "Never odd or even". An anagram uses exactly the same letters as another word or phrase, rearranged, like listen and silent. By convention both ignore capital letters, spaces and punctuation. The palindrome checker and the anagram checker do the comparison for you, and this guide covers the rules, some famous examples and how to make your own.

What counts as a palindrome

The usual rule compares letters only. "A man, a plan, a canal: Panama!" is a palindrome because once the capitals, spaces and punctuation are removed it reads amanaplanacanalpanama in both directions. Stricter versions exist: a character-by-character palindrome must match exactly, spaces and all, which the checker's Strict option tests. There are also word-unit palindromes, where whole words rather than letters mirror each other, as in "Fall leaves after leaves fall". A word that spells a different word backwards, such as stressed and desserts, is not a palindrome; it is sometimes called a semordnilap, which is palindromes spelled backwards. The reverse text tool is a quick way to find them.

Famous palindromes

• The Sator Square, a Latin word square found as graffiti at Pompeii, reads sator arepo tenet opera rotas and is a palindrome as a sentence.
• "A man, a plan, a canal: Panama" is credited to Leigh Mercer, published in 1948.
• Tattarrattat, James Joyce's word for a knock on the door in Ulysses, is a 12-letter palindrome.
• Saippuakivikauppias, Finnish for a soapstone seller, is a 19-letter palindrome often called the longest in everyday use.
• "Was it a car or a cat I saw?" and "Step on no pets" are popular short examples.

Dates can be palindromes too, but only in a given format: 22/02/2022 works when written day first.

Palindromic numbers and 196

Numbers such as 121 and 12321 are palindromes, and there is a famous game with them: reverse a number and add it to itself, and repeat until you reach a palindrome. 87 gets there in four steps: 87 + 78 = 165, 165 + 561 = 726, 726 + 627 = 1353, and 1353 + 3531 = 4884. Most numbers arrive quickly, but 89 takes 24 steps to reach 8813200023188. Then there is 196: nobody has ever produced a palindrome from it, despite enormous computer searches, and nobody has proved that it never will. Numbers like this are called Lychrel candidates, and 196 is the smallest. The checker's number section runs the game for you for up to 60 steps. Whether a number is a palindrome also depends on its base: 17 is not a palindrome in decimal, but in binary it is 10001, which is; Binary, explained from zero shows how to convert numbers to binary.

What makes an anagram

Two words or phrases are anagrams when they contain exactly the same letters, each used the same number of times. Dormitory and dirty room, astronomer and moon starer, and the eyes and they see are classics. Writers have used anagrams for pen names for centuries: the French writer François Rabelais published as Alcofribas Nasier, an exact anagram of his name. A good anagram uses every letter once with nothing left over, which is what separates it from a near miss.

How the checkers work

The palindrome checker strips everything except letters and digits, lowercases the text and removes accents so é matches e, then compares the first character with the last, the second with the second-to-last, and so on. If the phrase fails, it tells you the first mismatched pair and lists any palindromes of three or more letters hidden inside, such as racecar in a longer sentence. The anagram checker cleans both phrases the same way, sorts their letters and compares the results; its table shows each letter's count on both sides and highlights mismatches, so for apple and paper you can see the first has an extra l and the second an extra r. Neither searches a dictionary: they check the words you give them.

Making your own

Palindromes are easiest to build from the middle outwards: pick a centre such as a short word, then add letters to both ends in mirror order, testing as you go. Anagrams work best by writing the letters out, crossing them off as you form words, and checking the result. The word scramble game is good practice for seeing words in jumbled letters, and the crossword maker lets you use your finds as clues in a puzzle for friends.