gistfile1.rb

# BEFORE
>> a = User.new; a.valid?
>> a.errors.to_json
=> "[["name", "can't be blank"], ["password_confirmation", "can't be blank"], ["password", "can't be blank"], ["password", "is too short (minimum is 6 characters)"], ["email", "can't be blank"], ["email", "is too short (minimum is 6 characters)"], ["email", "should look like an email address."]]"

# config/initializers/sane_errors_to_json.rb

module ActiveRecord
  class Errors
    def to_json
      @errors.to_json
    end
  end
end

# AFTER

>> a = User.new; a.valid?
>> a.errors.to_json
=> "{"name": ["can't be blank"], "password_confirmation": ["can't be blank"], "password": ["can't be blank", "is too short (minimum is 6 characters)"], "email": ["can't be blank", "is too short (minimum is 6 characters)", "should look like an email address."]}"