Palindrome Checker

What a palindrome is and when to use this checker

A palindrome is any sequence of characters that reads the same forward and backward once you strip away formatting like spaces, punctuation, and letter case. Single words like "racecar," "level," and "civic" are the most familiar examples, but the same idea extends to full phrases ("A man, a plan, a canal, Panama") and to numbers (12321, 909, or a date written as 02/02/2020). This checker automates the comparison so you don't have to manually reverse a string and eyeball it, and it lets you control exactly which characters count via the three filter options.

Use it for word-game verification (Scrabble, crosswords, word puzzles), for checking programming-interview-style palindrome logic by hand, for classroom demonstrations of string manipulation, or just to settle a debate about whether a clever phrase you thought of actually qualifies as a palindrome.

The method

The checker applies your selected filters to the input, then compares the result to its own reversal:

• Ignore punctuation — removes any character that isn't a letter, digit, or space before comparison.
• Ignore spaces — removes all whitespace, so multi-word phrases are compared as one continuous string.
• Ignore letter case — converts everything to lowercase, so "Racecar" and "racecar" are treated identically.
• After filtering, the checker reverses the normalized string and checks whether it is identical to the original normalized string — if so, it is a palindrome.

Worked example

Take the phrase "A man a plan a canal Panama" with all three filters checked (the calculator's default). Removing punctuation leaves it unchanged (there is none), removing spaces gives "AmanaplanacanalPanama", and lowercasing gives "amanaplanacanalpanama". Reversing that string character by character gives back the exact same sequence: "amanaplanacanalpanama" — so the checker correctly reports "Yes, this is a palindrome!" with 21 characters checked, matching what the tool displays for this exact input.

Common mistakes and how to interpret the result

• Unchecking filters without realizing it changes the answer. "Racecar " with a trailing space, or "Race car" with an internal space, will fail the check if "ignore spaces" is unchecked, even though most people would call the phrase a palindrome.
• Expecting case-sensitive comparison by default. With "ignore letter case" checked (the default), "Level" and "level" are treated as the same — uncheck it only if you need a strict, case-sensitive comparison.
• Assuming numeric palindromes need special handling. Numbers are checked as character strings just like words — "12321" reversed is still "12321," so no separate numeric logic is needed.
• Forgetting that punctuation can hide a palindrome. A phrase with commas or periods (like "Madam, I'm Adam.") only reveals its palindrome structure once punctuation is stripped — leave that filter checked for natural-language phrases.

Frequently Asked Questions

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