Simple and agile Ruby data validation tool inspired by refinement types and functional approach

  • Powerful. Algebraic Data Type guarantees that gem is enough to implement any kind of complex data validation, while Functional Approach gives you full control over validation outcomes
  • Simple. You could write your first Refinment Type as simple as single Ruby method in single class
  • Brings transparency. Comes with instrumentation tools, so now you will exactly know how often each type matches in your production
  • Rubyish. DSL is inspired by Ruby Struct. If you love Ruby way you'd like the BloodContracts types
  • Born in production. Created on basis of eBaymag project, used as a tool to control and monitor data inside API communication
# Write your "types" as simple as...
class Email < ::BC::Refined
  REGEX = /\A[\w+\-.][email protected][a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i

  def match
    return if (context[:email] = value.to_s) =~ REGEX

class Phone < ::BC::Refined
  REGEX = /\A(\+7|8)(9|8)\d{9}\z/i

  def match
    return if (context[:phone] = value.to_s) =~ REGEX

# ... compose them...
Login = Email.or_a(Phone)

# ... and match!
case match = Login.match("not-a-login")
when Phone, Email
  match # use as you wish, you exactly know what kind of login you received
when BC::ContractFailure # translate error message
  match.messages # => [:no_matches, :invalid_phone, :invalid_email]
else raise # to make sure you covered all scenarios (Functional Way)

# And then in
# config/initializers/contracts.rb

module Contracts
  class YabedaInstrument
    def call(session)
      valid_marker = session.valid? ? "V" : "I"
      result = "[#{valid_marker}] #{session.result_type_name}"
      Yabeda.api_contract_matches.increment(result: result)

BloodContracts::Instrumentation.configure do |cfg|
  # Attach to every BC::Refined ancestor with Login in the name
  cfg.instrument "Login",


Add this line to your application's Gemfile:

gem 'blood_contracts'

And then execute:

$ bundle

Or install it yourself as:

$ gem install blood_contracts


This gem is just facade for the whole data validation and monitoring toolset.

For deeper understanding see BloodContracts::Core, BloodContracts::Ext and BloodContracts::Instrumentation


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the BloodContracts project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.