Validates HTML code against the W3C standards instantly as known as HTML linter. Supports partial HTML code validation. Errors and warnings including line numbers and excerpt code will be printed if any.

Validates YAML data against the YAML specification instantly as known as YAML linter. Errors including line numbers and excerpt code will be printed if any.

Safely validates a credit card number instantly to check if it's a valid card and find the card type. Completely works on your browser for your safety and privacy.

Tests a regular expression against any string instantly with matches highlighted including a cheat sheet and a reference.