Check Palindrome Number Online
Check whether a number is a palindrome in strict or digits-only mode, with nearest palindromes, binary palindrome, and repdigit stats. Free.
Type a number to find out if it reads the same forwards and backwards, plus the nearest palindromes, binary palindrome check, and repdigit flag.
Details
Nearest palindromes
Scans up to 1,000,000 steps in each direction and stops at the boundary if no palindrome is found.
How to Use Check Palindrome Number Online
- Type a number into the input field. Integers, decimals like
12.21, and negatives like-121are all accepted. - Pick a mode: "Digits only" (default) strips the sign and decimal point before comparing - so
-121and12.21become palindromes. "Strict" compares the exact string, so the minus sign or decimal point can break symmetry. - Watch the verdict: green for palindrome, amber for not - updates 150 ms after you stop typing.
- Scan the details card: digit count, reversed string, repdigit flag (all digits identical), and a bonus binary-palindrome flag when the integer value is small enough to fit in a safe integer.
- Check the neighbours: the closest palindromic integer before and after your input - handy for next-palindrome puzzles.
- Press
Ctrl+Enter(⌘+Enteron Mac) to force a check at any time. - Copy the summary or Download a timestamped `.txt` for sharing or archiving.
Frequently asked questions
What is a palindrome number?
A number whose string representation reads the same forwards and backwards. Examples: 121, 12321, 1001, 7337. The definition depends on how you represent the number – this tool makes the choice explicit via the mode selector.
Is my input uploaded anywhere?
No. The check runs entirely in your browser – a string reverse and a compare. Nothing touches the network.
What does “digits only” mode do?
It strips everything except 0-9 before comparing. That makes -121 → 121 (palindrome) and 12.21 → 1221 (palindrome). Useful when you care about the digit sequence regardless of formatting.
What does “strict” mode do?
It compares the exact trimmed string. So -121 is NOT a palindrome (the minus sign has no match on the right), and 12.21 IS a palindrome (the decimal point mirrors itself).
Are single-digit numbers palindromes?
Yes. 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 each read the same in both directions – the simplest case of palindromic numbers.
Can negative numbers be palindromes?
It depends on the mode. In “digits only” mode, negatives can be palindromes because the minus sign is stripped. In “strict” mode, the leading minus has no match on the right end so negatives are never palindromes.
What’s a binary palindrome?
A number whose base-2 (binary) representation is itself a palindrome. For example, 9 in binary is 1001, which is a palindrome. The tool shows this as a bonus stat when the input fits in a safe JavaScript integer.
What’s a repdigit?
A number with a single repeated digit (111, 4444, 77777). Every repdigit is a palindrome; the reverse also holds only for length-1 numbers.
How does the nearest-palindrome scan work?
A forward/backward linear scan over integers, bounded by a 1,000,000-step limit so very large inputs don’t freeze the tab. The boundary is almost never reached for normal inputs – the longest gap between palindromes up to a million is tens of steps.
Does it work offline?
After the page loads, yes. HTML, CSS, and JS are self-contained – disconnect Wi-Fi and keep checking.