diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..8eb3b06
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,12 @@
+/.bundle/
+/.yardoc
+/Gemfile.lock
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+
+# rspec failure tracking
+.rspec_status
diff --git a/.rspec b/.rspec
new file mode 100644
index 0000000..8c18f1a
--- /dev/null
+++ b/.rspec
@@ -0,0 +1,2 @@
+--format documentation
+--color
diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..6f2dd3a
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,11 @@
+Metrics/BlockLength:
+  Max: 120
+
+Metrics/LineLength:
+  Max: 110
+  
+Metrics/MethodLength:
+  Max: 12
+
+Style/Documentation:
+  Enabled: false
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..7df13ae
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,9 @@
+sudo: false
+language: ruby
+rvm:
+  - 2.4.0
+  - 2.3.3
+before_install:
+  - gem install bundler -v 1.14.6
+script:
+  - bundle exec rake
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 0000000..6a99ea1
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1,74 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, gender identity and expression, level of experience,
+nationality, personal appearance, race, religion, or sexual identity and
+orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+advances
+* Trolling, insulting/derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or electronic
+  address, without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting the project team at k1lowxb@gmail.com. All
+complaints will be reviewed and investigated and will result in a response that
+is deemed necessary and appropriate to the circumstances. The project team is
+obligated to maintain confidentiality with regard to the reporter of an incident.
+Further details of specific enforcement policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
+available at [http://contributor-covenant.org/version/1/4][version]
+
+[homepage]: http://contributor-covenant.org
+[version]: http://contributor-covenant.org/version/1/4/
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..f06c821
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+
+# Specify your gem's dependencies in faultline-rack.gemspec
+gemspec
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..017aba2
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2017 k1LoW
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..9ca21ad
--- /dev/null
+++ b/README.md
@@ -0,0 +1,34 @@
+# Faultline::Rack
+
+> [faultline](https://github.com/faultline/faultline) exception and error notifier for Rack application.
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+```ruby
+gem 'faultline-rack'
+```
+
+And then execute:
+
+    $ bundle
+
+Or install it yourself as:
+
+    $ gem install faultline-rack
+
+## Usage
+
+```ruby
+
+```
+
+## References
+
+- [airbrake/airbrake](https://github.com/airbrake/airbrake)
+    - Airbrake is licensed under [The MIT License (MIT)](https://github.com/airbrake/airbrake/LICENSE.md).
+
+## License
+
+MIT © Ken'ichiro Oyama
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..a32f908
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,8 @@
+require 'bundler/gem_tasks'
+require 'rspec/core/rake_task'
+require 'octorelease'
+require 'rubocop/rake_task'
+RSpec::Core::RakeTask.new(:spec)
+RuboCop::RakeTask.new
+
+task default: %i(spec rubocop)
diff --git a/bin/console b/bin/console
new file mode 100755
index 0000000..4d48ebd
--- /dev/null
+++ b/bin/console
@@ -0,0 +1,7 @@
+#!/usr/bin/env ruby
+
+require 'bundler/setup'
+require 'faultline/rack'
+
+require 'pry'
+Pry.start
diff --git a/bin/setup b/bin/setup
new file mode 100755
index 0000000..dce67d8
--- /dev/null
+++ b/bin/setup
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here
diff --git a/faultline-rack.gemspec b/faultline-rack.gemspec
new file mode 100644
index 0000000..1174052
--- /dev/null
+++ b/faultline-rack.gemspec
@@ -0,0 +1,38 @@
+# coding: utf-8
+
+lib = File.expand_path('../lib', __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+require 'faultline/rack/version'
+
+Gem::Specification.new do |spec|
+  spec.name          = 'faultline-rack'
+  spec.version       = Faultline::Rack::VERSION
+  spec.authors       = ['k1LoW']
+  spec.email         = ['k1lowxb@gmail.com']
+
+  spec.summary       = 'faultline exception and error notifier for Rack application'
+  spec.description   = 'faultline exception and error notifier for Rack application'
+  spec.homepage      = 'https://github.com/faultline/faultline-rack'
+  spec.license       = 'MIT'
+
+  spec.files         = `git ls-files -z`.split("\x0").reject do |f|
+    f.match(%r{^(test|spec|features)/})
+  end
+  spec.bindir        = 'exe'
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ['lib']
+
+  spec.add_runtime_dependency 'faultline', '~> 0.1'
+  spec.add_runtime_dependency 'airbrake', '~> 6.0'
+  spec.add_runtime_dependency 'rack', '~> 1'
+  spec.add_development_dependency 'bundler', '~> 1.14'
+  spec.add_development_dependency 'rake', '~> 10.0'
+  spec.add_development_dependency 'rspec', '~> 3.0'
+  spec.add_development_dependency 'rspec-wait', '~> 0'
+  spec.add_development_dependency 'webmock', '~> 2'
+  spec.add_development_dependency 'rack-test', '~> 0'
+  spec.add_development_dependency 'warden', '~> 1.2.6'
+  spec.add_development_dependency 'rubocop', '~> 0.47.0'
+  spec.add_development_dependency 'octorelease'
+  spec.add_development_dependency 'pry'
+end
diff --git a/lib/faultline/rack.rb b/lib/faultline/rack.rb
new file mode 100644
index 0000000..878dadc
--- /dev/null
+++ b/lib/faultline/rack.rb
@@ -0,0 +1,10 @@
+require 'faultline'
+require 'rack'
+require 'airbrake'
+require 'faultline/rack/version'
+require 'faultline/rack/middleware'
+
+module Faultline
+  module Rack
+  end
+end
diff --git a/lib/faultline/rack/middleware.rb b/lib/faultline/rack/middleware.rb
new file mode 100644
index 0000000..406eee6
--- /dev/null
+++ b/lib/faultline/rack/middleware.rb
@@ -0,0 +1,19 @@
+module Faultline
+  module Rack
+    class Middleware < Airbrake::Rack::Middleware
+      def initialize(app, notifier_name = :default)
+        @app = app
+        @notifier = Faultline[notifier_name]
+
+        # Prevent adding same filters to the same notifier.
+        return if @@known_notifiers.include?(notifier_name)
+        @@known_notifiers << notifier_name
+
+        return unless @notifier
+        RACK_FILTERS.each do |filter|
+          @notifier.add_filter(filter.new)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/faultline/rack/version.rb b/lib/faultline/rack/version.rb
new file mode 100644
index 0000000..7e27ab6
--- /dev/null
+++ b/lib/faultline/rack/version.rb
@@ -0,0 +1,5 @@
+module Faultline
+  module Rack
+    VERSION = '0.1.0'.freeze
+  end
+end
diff --git a/spec/apps/rack/dummy_app.rb b/spec/apps/rack/dummy_app.rb
new file mode 100644
index 0000000..2bbd74d
--- /dev/null
+++ b/spec/apps/rack/dummy_app.rb
@@ -0,0 +1,17 @@
+DummyApp = Rack::Builder.new do
+  use Rack::ShowExceptions
+  use Faultline::Rack::Middleware
+  use Warden::Manager
+
+  map '/' do
+    run(
+      proc do |_env|
+        [200, { 'Content-Type' => 'text/plain' }, ['Hello from index']]
+      end
+    )
+  end
+
+  map '/crash' do
+    run proc { |_env| raise FaultlineTestError }
+  end
+end
diff --git a/spec/faultline/rack/middleware_spec.rb b/spec/faultline/rack/middleware_spec.rb
new file mode 100644
index 0000000..f246614
--- /dev/null
+++ b/spec/faultline/rack/middleware_spec.rb
@@ -0,0 +1,145 @@
+require 'spec_helper'
+
+# rubocop:disable Style/DotPosition
+RSpec.describe Faultline::Rack::Middleware do
+  let(:app) do
+    proc { |env| [200, env, 'Bingo bango content'] }
+  end
+
+  let(:faulty_app) do
+    proc { raise FaultlineTestError }
+  end
+
+  let(:post_error_endpoint) do
+    'https://xxxxxxxxx.execute-api.ap-northeast-1.amazonaws.com/v0/projects/faultline-rack/errors'
+  end
+
+  let(:middleware) { described_class.new(app) }
+
+  def env_for(url, opts = {})
+    Rack::MockRequest.env_for(url, opts)
+  end
+
+  def wait_for_a_request_with_body(body)
+    wait_for(a_request(:post, post_error_endpoint).with(body: body)).to have_been_made.once
+  end
+
+  before do
+    stub_request(:post, post_error_endpoint).to_return(status: 201, body: '{}')
+  end
+
+  describe '#new' do
+    it "doesn't add filters if no notifiers are configured" do
+      expect do
+        expect(described_class.new(faulty_app, :unknown_notifier))
+      end.not_to raise_error
+    end
+  end
+
+  describe '#call' do
+    context 'when app raises an exception' do
+      context 'and when the notifier name is specified' do
+        let(:notifier_name) { :rack_middleware_initialize }
+
+        let(:bingo_post_error_endpoint) do
+          'https://xxxxxxxxx.execute-api.ap-northeast-1.amazonaws.com/v1/projects/faultline-bingo/errors'
+        end
+
+        let(:expected_body) do
+          /"errors":\[{"type":"FaultlineTestError"/
+        end
+
+        before do
+          Faultline.configure(notifier_name) do |c|
+            c.project = 'faultline-bingo'
+            c.api_key = 'xxxxXXXXXxXxXXxxXXXXXXXxxxxXXXXXX'
+            c.endpoint = 'https://xxxxxxxxx.execute-api.ap-northeast-1.amazonaws.com/v1'
+            c.logger = Logger.new('/dev/null')
+          end
+
+          stub_request(:post, bingo_post_error_endpoint).to_return(status: 201, body: '{}')
+        end
+
+        after { Faultline[notifier_name].close }
+
+        it 'notifies via the specified notifier' do
+          expect do
+            described_class.new(faulty_app, notifier_name).call(env_for('/'))
+          end.to raise_error(FaultlineTestError)
+
+          wait_for(
+            a_request(:post, bingo_post_error_endpoint).
+              with(body: expected_body)
+          ).to have_been_made.once
+
+          expect(
+            a_request(:post, post_error_endpoint).
+              with(body: expected_body)
+          ).not_to have_been_made
+        end
+      end
+
+      context 'and when the notifier is not configured' do
+        it 'rescues the exception, notifies Faultline & re-raises it' do
+          expect { described_class.new(faulty_app).call(env_for('/')) }.
+            to raise_error(FaultlineTestError)
+
+          wait_for_a_request_with_body(/"errors":\[{"type":"FaultlineTestError"/)
+        end
+
+        it 'sends framework version and name' do
+          expect { described_class.new(faulty_app).call(env_for('/bingo/bango')) }.
+            to raise_error(FaultlineTestError)
+
+          wait_for_a_request_with_body(
+            %r("context":{.*"version":"1.2.3 (Rails|Sinatra|Rack\.version)/.+".+})
+          )
+        end
+      end
+    end
+
+    context "when app doesn't raise" do
+      context 'and previous middleware stored an exception in env' do
+        shared_examples 'stored exception' do |type|
+          it "notifies on #{type}, but doesn't raise" do
+            env = env_for('/').merge(type => FaultlineTestError.new)
+            described_class.new(app).call(env)
+
+            wait_for_a_request_with_body(/"errors":\[{"type":"FaultlineTestError"/)
+          end
+        end
+
+        ['rack.exception', 'action_dispatch.exception', 'sinatra.error'].each do |type|
+          include_examples 'stored exception', type
+        end
+      end
+
+      it "doesn't notify Faultline" do
+        described_class.new(app).call(env_for('/'))
+        sleep 1
+        expect(a_request(:post, post_error_endpoint)).not_to have_been_made
+      end
+    end
+
+    it 'returns a response' do
+      response =  described_class.new(app).call(env_for('/'))
+
+      expect(response[0]).to eq(200)
+      expect(response[1]).to be_a(Hash)
+      expect(response[2]).to eq('Bingo bango content')
+    end
+  end
+
+  context 'when Faultline is not configured' do
+    it 'returns nil' do
+      allow(Faultline[:default]).to receive(:build_notice).and_return(nil)
+      allow(Faultline[:default]).to receive(:notify)
+
+      expect { described_class.new(faulty_app).call(env_for('/')) }.
+        to raise_error(FaultlineTestError)
+
+      expect(Faultline[:default]).to have_received(:build_notice)
+      expect(Faultline[:default]).not_to have_received(:notify)
+    end
+  end
+end
diff --git a/spec/faultline/rack_spec.rb b/spec/faultline/rack_spec.rb
new file mode 100644
index 0000000..27b5e56
--- /dev/null
+++ b/spec/faultline/rack_spec.rb
@@ -0,0 +1,7 @@
+require 'spec_helper'
+
+RSpec.describe Faultline::Rack do
+  it 'has a version number' do
+    expect(Faultline::Rack::VERSION).not_to be nil
+  end
+end
diff --git a/spec/integration/rack/rack_spec.rb b/spec/integration/rack/rack_spec.rb
new file mode 100644
index 0000000..e7fff54
--- /dev/null
+++ b/spec/integration/rack/rack_spec.rb
@@ -0,0 +1,17 @@
+require 'spec_helper'
+require 'integration/shared_examples/rack_examples'
+
+RSpec.describe 'Rack integration specs' do
+  let(:app) { DummyApp }
+
+  include_examples 'rack examples'
+
+  describe 'context payload' do
+    it 'includes version' do
+      get '/crash'
+      wait_for_a_request_with_body(
+        /"context":{.*"version":"1.2.3 Rack\.version.+Rack\.release/
+      )
+    end
+  end
+end
diff --git a/spec/integration/shared_examples/rack_examples.rb b/spec/integration/shared_examples/rack_examples.rb
new file mode 100644
index 0000000..5928c6e
--- /dev/null
+++ b/spec/integration/shared_examples/rack_examples.rb
@@ -0,0 +1,129 @@
+RSpec.shared_examples 'rack examples' do
+  include Warden::Test::Helpers
+
+  after { Warden.test_reset! }
+
+  let(:post_error_endpoint) do
+    'https://xxxxxxxxx.execute-api.ap-northeast-1.amazonaws.com/v0/projects/faultline-rack/errors'
+  end
+
+  def wait_for_a_request_with_body(body)
+    wait_for(a_request(:post, post_error_endpoint).with(body: body)).to have_been_made.once
+  end
+
+  before do
+    # Make sure the Logger integration doesn't get in the way.
+    allow_any_instance_of(Logger).to receive(:airbrake_notifier).and_return(nil)
+
+    stub_request(:post, post_error_endpoint).to_return(status: 201, body: '{}')
+  end
+
+  describe 'application routes' do
+    describe '/index' do
+      it 'successfully returns 200 and body' do
+        get '/'
+
+        expect(last_response.status).to eq(200)
+        expect(last_response.body).to eq('Hello from index')
+
+        wait_for(a_request(:post, post_error_endpoint)).not_to have_been_made
+      end
+    end
+
+    describe '/crash' do
+      it 'returns 500 and sends a notice to Airbrake' do
+        get '/crash'
+
+        expect(last_response.status).to eq(500)
+        wait_for_a_request_with_body(/"errors":\[{"type":"FaultlineTestError"/)
+      end
+    end
+  end
+
+  describe 'context payload' do
+    context 'when the user is present' do
+      let(:common_user_params) do
+        { id: 1, email: 'qa@example.com', username: 'qa-dept' }
+      end
+
+      before do
+        login_as(OpenStruct.new(user_params))
+        get '/crash'
+      end
+
+      context 'when the user has first and last names' do
+        let(:user_params) do
+          common_user_params.merge(first_name: 'Bingo', last_name: 'Bongo')
+        end
+
+        it "reports the user's first and last names" do
+          wait_for_a_request_with_body(/
+            "context":{.*
+              "user":{
+                "id":"1",
+                "name":"Bingo\sBongo",
+                "username":"qa-dept",
+                "email":"qa@example.com"}
+          /x)
+        end
+      end
+
+      context 'when the user has only name' do
+        let(:user_params) do
+          common_user_params.merge(name: 'Bingo')
+        end
+
+        it "reports the user's name" do
+          wait_for_a_request_with_body(/
+            "context":{.*
+              "user":{
+                "id":"1",
+                "name":"Bingo",
+                "username":"qa-dept",
+                "email":"qa@example.com"}
+          /x)
+        end
+      end
+    end
+
+    context 'when additional parameters present' do
+      before do
+        get '/crash', nil, 'HTTP_USER_AGENT' => 'Bot', 'HTTP_REFERER' => 'bingo.com'
+      end
+
+      it 'features url' do
+        wait_for_a_request_with_body(
+          %r("context":{.*"url":"http://example\.org/crash".*})
+        )
+      end
+
+      it 'features hostname' do
+        wait_for_a_request_with_body(/"context":{.*"hostname":".+".*}/)
+      end
+
+      it 'features userAgent' do
+        wait_for_a_request_with_body(/"context":{.*"userAgent":"Bot".*}/)
+      end
+    end
+  end
+
+  describe 'environment payload' do
+    before do
+      get '/crash', nil, 'HTTP_REFERER' => 'bingo.com'
+    end
+
+    it 'features referer' do
+      wait_for_a_request_with_body(/"environment":{.*"referer":"bingo.com".*}/)
+    end
+
+    it 'contains HTTP headers' do
+      wait_for_a_request_with_body(
+        /"environment":{.*"headers":{.*"CONTENT_LENGTH":"0".*}/
+      )
+    end
+
+    it 'contains HTTP method' do
+      wait_for_a_request_with_body(/"environment":{.*"httpMethod":"GET".*}/)
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..0da970b
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,37 @@
+require 'bundler/setup'
+require 'webmock'
+require 'webmock/rspec'
+require 'rspec/wait'
+require 'rack'
+require 'rack/test'
+require 'rake'
+require 'pry'
+require 'faultline/rack'
+
+Faultline.configure do |c|
+  c.project = 'faultline-rack'
+  c.api_key = 'xxxxXXXXXxXxXXxxXXXXXXXxxxxXXXXXX'
+  c.endpoint = 'https://xxxxxxxxx.execute-api.ap-northeast-1.amazonaws.com/v0'
+  c.app_version = '1.2.3'
+  c.logger = Logger.new('/dev/null')
+  c.workers = 5
+end
+
+RSpec.configure do |config|
+  # Enable flags like --only-failures and --next-failure
+  config.example_status_persistence_file_path = '.rspec_status'
+
+  config.order = 'random'
+  config.color = true
+  config.disable_monkey_patching!
+  config.wait_timeout = 3
+
+  config.include Rack::Test::Methods
+end
+
+require 'warden'
+require 'apps/rack/dummy_app'
+
+Thread.abort_on_exception = true
+
+FaultlineTestError = Class.new(StandardError)