Validacity adds an extra layer of validation objects where all your validation logic can be moved to.

Mount to an endpoint of your application, give it forms fields, and it'll return the validations errors/success in JSON. Really usefull when you want to add on-unblur or before-submit validations.

A Rails 3.1 & 3.2 version of Encrypted Cookie Store by FooBarWidget

Params validations for Ruby on Rails

validate-response is a gem for bringing error messages from one or more ActiveRecord objects to the unified structure & highlight validation errors in forms (ajax supported).

ActiveRecord model validation against stopforumspam.com (Rails 3)

Brazilian zipcode validations for ActiveRecord, integrated with correios-cep gem.

ActiveRecord validations for danish CVR numbers

Some description for validates-gem

Use those validators for Australian numbers as ABN, TFN, ...

SWIFT validator for ActiveRecord attributes.

Validates TeamViewer ID for ActiveRecord attributes.

Validate if an association has unique values on a specific attribute.

A notifier for form validation errors.

Find and report ActiveRecord validation errors.

A extension activemodel's validations to validation step by step.

Reuse your Rails model validations on the client-side.

Tracks each validation error, providing an aggregate to identify UI issues

Checks whether an ActiveModel Validator is attached to an attribute of a Model and with which options

Rails 3 generator plugin that generates validator's skeleton files.