Card Number Checksum (Luhn) Validator

About the Card Number Checksum (Luhn) Validator

Card numbers, IMEI numbers and many ID numbers end with a Luhn check digit that catches typing mistakes. Enter a number to see whether its checksum is valid and which card network its prefix suggests. Developers use it to test payment forms with official test numbers; nothing is ever sent or stored.

How to use it

1. Type the number — spaces and dashes are fine.
2. See whether the Luhn checksum passes.
3. Check the detected network for card numbers.

Tips and good to know

• 4111 1111 1111 1111 is a widely used Visa test number.
• A valid checksum does not mean a card exists or can be charged.
• The Luhn check catches any single wrong digit and most swapped neighbours.
• Never paste real customer card numbers into any website.

About developer tools

Developer utilities are some of the most-searched tools online because everyone who touches code needs them, and they are usually needed right now: a minified API response to read, a Base64 string to decode, a token to inspect, a regular expression to debug. The risk with many online versions is that you paste secrets — API keys, tokens, customer data — into a server you know nothing about.

Every developer tool here runs entirely in JavaScript inside your browser tab and uses the standard Web Crypto and encoding APIs where relevant. You can open your browser's network panel and confirm that nothing is transmitted when you use them. Even so, treat production secrets with care: rotate any credential you have shared anywhere you did not intend.

These utilities follow the relevant open standards — RFC 8259 for JSON, RFC 4648 for Base64, RFC 3986 for URL encoding, RFC 7519 for JSON Web Tokens and FIPS 180-4 for the SHA family of hashes — so results match what your servers, libraries and command-line tools produce. Where browsers differ from other runtimes, such as JavaScript's regular expression flavour, the page says so. They are deliberately small and dependency-free so they load quickly on slow connections and keep working as browsers evolve. If a result surprises you, the guide on each page lists the most common causes, which are usually invisible characters, encoding mismatches or copied whitespace.

Popular ways people use developer tools

• Reading a minified API response while debugging an integration or a webhook payload.
• Inspecting a login token to see which claims it carries and exactly when it expires.
• Building and testing a regular expression for form validation before shipping it to users.
• Generating unique IDs for test fixtures, seed data or database migrations.
• Producing a checksum to confirm that a downloaded or copied file has not been altered.

How we build and test our free tools

Every tool in this collection is built and tested by The Curator team. Before a tool is published we check it against known reference results — textbook loan schedules, standard test vectors for hashes, sample files for conversions — and we re-check it whenever browsers change. Each page explains the method so you can verify the answer yourself rather than take it on trust.

The tools run as JavaScript inside your browser tab. When you choose a file, your browser reads it from your disk into memory; the tool processes it and gives you the result as a download. No copy is sent to us or to anyone else, and nothing is kept after you close the tab. That is why these tools are safe for personal documents, and why they keep working on a slow or interrupted connection once the page has loaded.

The collection is free because it is supported by advertising on these guide pages. We never charge for a tool, never add watermarks and never sell what you type. If something doesn't work as described, or you would like a tool we don't have yet, please contact us — new tools are added in regular batches based on what readers ask for.

Frequently asked questions

Is this safe?

The check happens in your browser and nothing is transmitted, but use test numbers anyway.

What else uses Luhn?

IMEI phone identifiers, Canadian social insurance numbers and many loyalty card numbers.

Is my input stored or sent anywhere?

No. Everything runs inside your browser tab and disappears when you close it.

Is the Card Number Checksum (Luhn) Validator really free?

Yes. There is no account, no trial and no watermark. The Curator is supported by advertising on its guide pages, never by charging for tools or selling your data.

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