Simple client side validation that keeps validation in the models

Realtime remote form input validations delivered via websockets

ActiveValidators is a collection of ActiveModel/ActiveRecord validations

Simple model and validation mixins for RubyMotion

A gem/plugin for Rails 3+ that enables client-side validation using ActiveModel + HTML5

Robust options validation for methods.

A Ruby wrapper for the World Wide Web Consortium’s online validation services.

Rails plugin that maps model validations to class names on form elements to integrate with Validatious.

Phone number parsing, validation and formatting

Regressor generates regression specs based on ActiveRecord models. Currently relations, validations, attributes, and database indexes are supported.

ActiveRecord Tableless Models provides a simple mixin for creating models that are not bound to the database. This approach is useful for taking advantage of the features of ActiveRecord such as validation, relationships, etc.

Includes a couple of core functions such as callbacks, timestamping, typecasting and lots of generic validation routines.

Introspects your database string field maximum lengths and automatically defines length validations.

Minimalist validation matcher

cucumber-api allows API JSON response validation and verification in BDD style.

Machinery is a systems management toolkit for Linux. It supports configuration discovery, system validation, and service migration. It's based on the idea of a universal system description.

A gem that provides credit card validation. It is basically a ruby port of the javascript credit card validator by Thomas Fuchs (madrobby) (http://github.com/madrobby/creditcard_js).

Add a validation filter to your controller.

Automatically includes Modules from app/concerns/<module_with_concerns>/<concern>.rb into <module_with_concerns> to ease monkey-patching associations and validations on ActiveRecord::Base descendents from other gems when layering schemas.

Rack middleware for Weixin apps: message validation/parser/generator