How to Validate Emails, URLs, IPv4 Addresses and Credit Card Numbers in Your Browser
Learn what each validation mode actually checks, from the email pattern and URL parser to the IPv4 regex and the Luhn checksum for card numbers.
Universal Format Validator
Introduction
Malformed emails, URLs, IP addresses and card numbers cause failed signups, broken integrations and rejected payments. The Universal Format Validator checks a single string against one of four syntax rules and reports Valid Format or Invalid Syntax immediately. Every check runs locally in the browser, so the value you paste is never transmitted.
Step-by-Step Instructions
- Choose a mode from the switcher: Email Address, URL Endpoint, IPv4 Address or Credit Card (Luhn).
- Paste or type the value in the text field labelled Type string value to validate.
- Read the result badge, which shows Valid Format in green or Invalid Syntax in red.
- Edit the value in place to see the badge update on every keystroke.
- Switch to another mode to test the same string against a different rule.
Key Use Cases
- Form Debugging: Check why a user's email keeps failing your signup validation.
- Config Review: Confirm an API endpoint includes a scheme and parses as a valid URL.
- Test Card Data: Verify that a sample card number passes the Luhn checksum before using it in a payment sandbox.
Frequently Asked Questions
Does the tool verify that an email address or domain actually exists?
No. Email mode checks the shape only: at least one character, an @ sign, a domain part and a dot, with no spaces. It does not look up DNS records or confirm the mailbox exists.
Why is example.com reported as an invalid URL?
URL mode uses the browser's built-in URL parser, which requires a scheme such as https:// or ftp://. A bare domain without a scheme fails to parse, so add the protocol prefix to validate it.
What does the Credit Card (Luhn) check actually confirm?
It strips every non-digit character, requires 13 to 19 digits, then runs the Luhn mod-10 checksum. A pass means the number is structurally valid, not that the card is real, active or has funds. IPv4 mode similarly checks only dotted-quad syntax and does not accept IPv6 or CIDR notation.