Headhunter is an HTML and CSS validation tool that injects itself into your Rails feature tests and automagically checks all your generated HTML and CSS for validity. In addition, it also looks out for unused (and therefore superfluous) CSS selectors.

Encapsulate form logic and validations in a simple object

Personnummer handles validation of Swedish personal identity numbers.

A development toolkit for Ruby with several small/cohesive abstractions (monads, enums, business logic, data validation...) to empower your development workflow - It's totally free of dependencies.

Easily add Judge client side validation to your SimpleForm forms.

This gem preps a new Rails app with some of the best Rails gems and Jquery sweetness available( Twitter-Bootstrap, Devise, CanCan, Rails Admin, Spreadsheet, ) Not only does it takes care of the installation of these gems, it also extends your scaffolds to give aesthetically improved views. Furthe...

Keep your code DRY by inferring column validations from table properties! Automagically validate presence, length, numericality, inclusion and uniqueness of ActiveRecord backed columns.

IBAN + SWIFT/BIC: Information, Validation and Formatting.

This library helps validate attributes to specific types in the same way that ActiveModel valiations work. Able to chain additional modifiers to each validation.

Handles application errors and model validations

Ruby gem for runtime data validation and monitoring using the contracts approach.

Membrane provides an easy to use DSL for specifying validation logic declaratively.

Checks required env variables and its format using dotenv and .env.sample files. Sample files include validation documentation which is interpreted and used to validate your environment.

Swift code validation and lookup Ruby gem

Token validation for distributed resource servers

ActiveModel validation that checks email addresses against a blacklist of trash-mail providers

Validate iTunes Transaction and Unified style receipts with local decoding and remote validation.

A Ruby Library for dealing with validation cryptocurrency adresses.

Decode iTunes OS X and iOS receipts without remote server-side validation by using the Apple Inc Root Certificate.

Provide validation/generation for UPC/EAN/GTIN numbers