Validators & Checkers
Validate addresses, structured data and identifiers locally in your browser.
Email Validator
Check whether an email address matches the common dot-atom syntax.
JSON Validator
Check whether text is syntactically valid JSON and see its parsed shape.
UUID Validator
Check whether a string is a canonical RFC 9562 UUID and read its version.
IP Address Validator
Check whether a string is a valid IPv4 address or IPv6 address, including compressed forms.
IBAN Validator
Check an IBAN's structure, country length and ISO 7064 checksum.
ISBN Validator
Check an ISBN-10 or ISBN-13 checksum after removing hyphens and spaces.
Phone Number Validator
Check whether a phone number matches the structural E.164 format.
Password Strength Checker
Score a password's length, character variety and repeated patterns locally.
XML Validator
Check whether XML is well-formed using the same parser as the XML converters.
VAT Number Validator
Check a VAT registration number's format against its country's expected pattern.
HTML Validator
Check HTML for unclosed tags, mismatched nesting and duplicate IDs.
CSS Validator
Check CSS for unclosed braces, brackets, strings and comments.
What this category covers
Local, browser-based validation for identifiers and structured data: email addresses, IBANs, ISBNs, phone numbers, JSON, XML, HTML, CSS, UUIDs, IP addresses, VAT numbers and password strength — each checked against its real specification, not just a loose pattern.
How to choose the right tool
Format-only checks (Email Validator, UUID Validator, IP Address Validator) confirm a value is syntactically valid. Checksum-backed validators (IBAN Validator, ISBN Validator) go further and verify the value is mathematically consistent — not just shaped correctly. Structured-document validators (JSON Validator, XML Validator, HTML Validator, CSS Validator) parse the full document and report the first syntax error. VAT Number Validator checks only the country-specific format, since VAT numbers aren't checksummed the way IBANs are — pair it with an official VIES lookup before trusting a number for invoicing. Password Strength Checker scores an entered password without ever sending it anywhere.
Common use cases
A developer validates a webhook payload's JSON before parsing it; an accountant checks an IBAN before wiring an international payment; a publisher confirms an ISBN before listing a book; a support team verifies a customer's phone number format before dialing; a user checks their new password's strength before setting it as their account password.