Validators

Check the WCAG contrast ratio between two colors, with pass/fail results for AA and AAA at both text sizes.

Check a card number’s format with the Luhn checksum and detect its likely network.

Validate a 5-field cron expression and see its schedule described in plain English.

Check whether an email address is correctly formatted, with a plain-English reason when it isn’t.

Check an IBAN’s format and mod-97 checksum, with country/length and checksum shown separately.

Validate ISBN-10 and ISBN-13 checksums with auto-detection, plus convert between the two formats.

Compare two JSON values and see exactly which keys were added, removed, or changed.

Check a password against length and character-variety rules, with a live strength meter.

Validate a phone number’s format for the US, UK, India, or international E.164 notation.

Check whether a string is a valid, URL-safe slug and get a corrected suggestion if not.

Check whether a string is a valid URL and see it broken into protocol, host, path, and more.