diff --git a/Guardfile b/Guardfile
index 1542d79..e4f2f3e 100644
--- a/Guardfile
+++ b/Guardfile
@@ -9,6 +9,8 @@ group :sinatra do
           all_on_start: true,
           cmd: "RACK_ENV=#{env} bundle exec appraisal sinatra14 rspec" do
       watch(%r{^spec/integration/sinatra_spec.rb$})
+      watch('lib/loga/context_manager.rb')
+      watch('spec/loga/context_manager_spec.rb')
     end
   end
 end
@@ -34,6 +36,8 @@ group :rails do
         end
 
         watch(%r{^spec/integration/rails/.+_spec\.rb$})
+        watch('lib/loga/context_manager.rb')
+        watch('spec/loga/context_manager_spec.rb')
       end
     end
   end
@@ -50,6 +54,8 @@ group :sidekiq do
         'spec/loga/sidekiq_spec.rb',
       ]
     end
+    watch('lib/loga/context_manager.rb')
+    watch('spec/loga/context_manager_spec.rb')
   end
 end
 
@@ -57,5 +63,7 @@ group :unit do
   guard :rspec, cmd: 'bundle exec appraisal unit rspec' do
     watch(%r{^spec/unit/.+_spec\.rb$})
     watch(%r{^lib/(.+)\.rb$}) { |m| "spec/unit/#{m[1]}_spec.rb" }
+    watch('lib/loga/context_manager.rb')
+    watch('spec/loga/context_manager_spec.rb')
   end
 end
diff --git a/lib/loga.rb b/lib/loga.rb
index 20242c8..04285a6 100644
--- a/lib/loga.rb
+++ b/lib/loga.rb
@@ -9,32 +9,53 @@
 require 'loga/rack/request_id'
 require 'loga/railtie' if defined?(Rails)
 require 'loga/sidekiq'
+require 'loga/context_manager'
 
 module Loga
   ConfigurationError = Class.new(StandardError)
 
-  def self.configuration
-    unless @configuration
-      raise ConfigurationError,
-            'Loga has not been configured. Configure with Loga.configure(options)'
+  class << self
+    def configuration
+      unless @configuration
+        raise ConfigurationError,
+              'Loga has not been configured. Configure with Loga.configure(options)'
+      end
+
+      @configuration
     end
 
-    @configuration
-  end
+    def configure(options, framework_options = {})
+      raise ConfigurationError, 'Loga has already been configured' if @configuration
 
-  def self.configure(options, framework_options = {})
-    raise ConfigurationError, 'Loga has already been configured' if @configuration
+      @configuration ||= Configuration.new(options, framework_options)
 
-    @configuration ||= Configuration.new(options, framework_options)
+      Loga::Sidekiq.configure_logging
+    end
 
-    Loga::Sidekiq.configure_logging
-  end
+    def logger
+      configuration.logger
+    end
 
-  def self.logger
-    configuration.logger
-  end
+    def reset
+      @configuration = nil
+    end
 
-  def self.reset
-    @configuration = nil
+    def attach_context(payload)
+      current_context.attach_context(payload)
+    end
+
+    def clear_context
+      current_context.clear
+    end
+
+    def retrieve_context
+      current_context.retrieve_context
+    end
+
+    private
+
+    def current_context
+      ContextManager.current
+    end
   end
 end
diff --git a/lib/loga/configuration.rb b/lib/loga/configuration.rb
index f0e22ec..43d0867 100644
--- a/lib/loga/configuration.rb
+++ b/lib/loga/configuration.rb
@@ -14,44 +14,42 @@ class Configuration
       Sinatra::NotFound
     ].freeze
 
-    attr_accessor :device, :filter_exceptions, :filter_parameters,
-                  :host, :level, :service_version, :sync, :tags, :hide_pii
-    attr_reader :logger, :format, :service_name
+    attr_reader :device, :filter_exceptions, :filter_parameters, :format, :hide_pii,
+                :host, :level, :service_name, :service_version, :sync, :tags
 
-    # rubocop:disable Metrics/MethodLength
     def initialize(user_options = {}, framework_options = {})
       options = default_options.merge(framework_options)
                                .merge(environment_options)
                                .merge(user_options)
 
-      self.device            = options[:device]
-      self.filter_exceptions = options[:filter_exceptions]
-      self.filter_parameters = options[:filter_parameters]
-      self.format            = options[:format]
-      self.host              = options[:host]
-      self.level             = options[:level]
-      self.service_name      = options[:service_name]
-      self.service_version   = options[:service_version] || ServiceVersionStrategies.call
-      self.sync              = options[:sync]
-      self.tags              = options[:tags]
-      self.hide_pii          = options[:hide_pii]
+      @device            = options[:device]
+      @filter_exceptions = options[:filter_exceptions]
+      @filter_parameters = options[:filter_parameters]
+      @format            = options[:format].to_s.to_sym
+      @hide_pii          = options[:hide_pii]
+      @host              = options[:host]
+      @level             = options[:level]
+      @service_name      = options[:service_name].to_s.strip
+      @service_version   = options[:service_version] || ServiceVersionStrategies.call
+      @sync              = options[:sync]
+      @tags              = options[:tags]
 
       validate
-
-      @logger = initialize_logger
     end
-    # rubocop:enable Metrics/MethodLength
 
-    def format=(name)
-      @format = name.to_s.to_sym
+    def structured?
+      format == :gelf
     end
 
-    def service_name=(name)
-      @service_name = name.to_s.strip
-    end
+    def logger
+      @logger ||= begin
+        device.sync          = sync
+        new_logger           = Logger.new(device)
+        new_logger.formatter = assign_formatter
+        new_logger.level     = constantized_log_level
 
-    def structured?
-      format == :gelf
+        TaggedLogging.new(new_logger)
+      end
     end
 
     private
@@ -79,14 +77,6 @@ def environment_options
       { format: ENV['LOGA_FORMAT'].presence }.reject { |_, v| v.nil? }
     end
 
-    def initialize_logger
-      device.sync      = sync
-      logger           = Logger.new(device)
-      logger.formatter = assign_formatter
-      logger.level     = constantized_log_level
-      TaggedLogging.new(logger)
-    end
-
     def constantized_log_level
       Logger.const_get(level.to_s.upcase)
     end
@@ -98,15 +88,13 @@ def hostname
     end
 
     def assign_formatter
-      if format == :gelf
-        Formatters::GELFFormatter.new(
-          service_name:    service_name,
-          service_version: service_version,
-          host:            host,
-        )
-      else
-        Formatters::SimpleFormatter.new
-      end
+      return Formatters::SimpleFormatter.new if format != :gelf
+
+      Formatters::GELFFormatter.new(
+        service_name:    service_name,
+        service_version: service_version,
+        host:            host,
+      )
     end
   end
 end
diff --git a/lib/loga/context_manager.rb b/lib/loga/context_manager.rb
new file mode 100644
index 0000000..1204455
--- /dev/null
+++ b/lib/loga/context_manager.rb
@@ -0,0 +1,31 @@
+require 'thread'
+
+module Loga
+  class ContextManager
+    def self.current
+      Thread.current[:__loga_context_manager] ||= new
+    end
+
+    def initialize
+      @semaphore = Mutex.new
+
+      clear
+    end
+
+    def clear
+      @semaphore.synchronize do
+        @context = {}
+      end
+    end
+
+    def attach_context(payload)
+      @semaphore.synchronize do
+        @context.update(payload)
+      end
+    end
+
+    def retrieve_context
+      @semaphore.synchronize { @context }
+    end
+  end
+end
diff --git a/lib/loga/formatters/gelf_formatter.rb b/lib/loga/formatters/gelf_formatter.rb
index bbc9b40..bbaa13b 100644
--- a/lib/loga/formatters/gelf_formatter.rb
+++ b/lib/loga/formatters/gelf_formatter.rb
@@ -48,12 +48,15 @@ def build_event(time, message)
 
         event.timestamp ||= time
         event.data ||= {}
-        event.data.tap do |hash|
-          hash.merge! compute_exception(event.exception)
-          hash.merge! compute_type(event.type)
+
+        event.data.tap do |data_hash|
+          data_hash.merge!(compute_exception(event.exception))
+          data_hash.merge!(compute_type(event.type))
           # Overwrite hash with Loga's additional fields
-          hash.merge! loga_additional_fields
+          data_hash.merge!(loga_additional_fields)
+          data_hash.merge!(Loga.retrieve_context)
         end
+
         event
       end
 
diff --git a/lib/loga/rack/logger.rb b/lib/loga/rack/logger.rb
index 81e880b..f6cffad 100644
--- a/lib/loga/rack/logger.rb
+++ b/lib/loga/rack/logger.rb
@@ -43,7 +43,7 @@ def set_data
         data['request_ip'] = request.ip
         data['user_agent'] = request.user_agent
         data['controller'] = request.controller_action_name if request.controller_action_name
-        data['duration']   = duration_in_ms(started_at, Time.now)
+        data['duration']   = duration_in_ms(started_at)
       end
       # rubocop:enable Metrics/LineLength
 
@@ -55,6 +55,7 @@ def send_message
           timestamp:  started_at,
           type:       'request',
         )
+
         logger.public_send(compute_level, event)
       end
 
diff --git a/spec/fixtures/rails32.rb b/spec/fixtures/rails32.rb
index f4ba24f..eb029c7 100644
--- a/spec/fixtures/rails32.rb
+++ b/spec/fixtures/rails32.rb
@@ -49,6 +49,12 @@ def update
     @id = params[:id]
     render '/user'
   end
+
+  def attach_context
+    Loga.attach_context(animal: 'monkey')
+
+    render json: { hello: :world }
+  end
 end
 
 class FakeMailer < ActionMailer::Base
@@ -68,6 +74,27 @@ def basic_mail
   end
 end
 
+class FakeMailerWithContext < ActionMailer::Base
+  default from: 'notifications@example.com'
+
+  def self.send_email
+    Loga.attach_context(tshirt_size: 'XL')
+    Loga.attach_context(height: 155)
+    Loga.attach_context(weight: 122)
+
+    basic_mail.deliver
+  end
+
+  def basic_mail
+    mail(
+      to: 'user@example.com',
+      subject: 'Welcome to My Awesome Site',
+      body: 'Banana muffin',
+      content_type: 'text/html',
+    )
+  end
+end
+
 Dummy.routes.append do
   get 'ok'        => 'application#ok'
   get 'error'     => 'application#error'
@@ -75,6 +102,8 @@ def basic_mail
   post 'users'    => 'application#create'
   get 'new'       => 'application#new'
   put 'users/:id' => 'application#update'
+
+  get 'attach_context' => 'application#attach_context'
 end
 
 Dummy.initialize!
diff --git a/spec/fixtures/rails40.rb b/spec/fixtures/rails40.rb
index b33aa20..7b060b1 100644
--- a/spec/fixtures/rails40.rb
+++ b/spec/fixtures/rails40.rb
@@ -49,6 +49,12 @@ def update
     @id = params[:id]
     render '/user'
   end
+
+  def attach_context
+    Loga.attach_context(animal: 'monkey')
+
+    render json: { hello: :world }
+  end
 end
 
 class FakeMailer < ActionMailer::Base
@@ -68,6 +74,27 @@ def basic_mail
   end
 end
 
+class FakeMailerWithContext < ActionMailer::Base
+  default from: 'notifications@example.com'
+
+  def self.send_email
+    Loga.attach_context(tshirt_size: 'XL')
+    Loga.attach_context(height: 155)
+    Loga.attach_context(weight: 122)
+
+    basic_mail.deliver
+  end
+
+  def basic_mail
+    mail(
+      to: 'user@example.com',
+      subject: 'Welcome to My Awesome Site',
+      body: 'Banana muffin',
+      content_type: 'text/html',
+    )
+  end
+end
+
 Dummy.routes.append do
   get 'ok'        => 'application#ok'
   get 'error'     => 'application#error'
@@ -75,6 +102,8 @@ def basic_mail
   post 'users'    => 'application#create'
   get 'new'       => 'application#new'
   put 'users/:id' => 'application#update'
+
+  get 'attach_context' => 'application#attach_context'
 end
 
 Dummy.initialize!
diff --git a/spec/fixtures/rails42.rb b/spec/fixtures/rails42.rb
index 6e7995c..c02c9eb 100644
--- a/spec/fixtures/rails42.rb
+++ b/spec/fixtures/rails42.rb
@@ -49,6 +49,12 @@ def update
     @id = params[:id]
     render '/user'
   end
+
+  def attach_context
+    Loga.attach_context(animal: 'monkey')
+
+    render json: { hello: :world }
+  end
 end
 
 class FakeMailer < ActionMailer::Base
@@ -68,6 +74,27 @@ def basic_mail
   end
 end
 
+class FakeMailerWithContext < ActionMailer::Base
+  default from: 'notifications@example.com'
+
+  def self.send_email
+    Loga.attach_context(tshirt_size: 'XL')
+    Loga.attach_context(height: 155)
+    Loga.attach_context(weight: 122)
+
+    basic_mail.deliver_now
+  end
+
+  def basic_mail
+    mail(
+      to: 'user@example.com',
+      subject: 'Welcome to My Awesome Site',
+      body: 'Banana muffin',
+      content_type: 'text/html',
+    )
+  end
+end
+
 Dummy.routes.append do
   get 'ok'        => 'application#ok'
   get 'error'     => 'application#error'
@@ -75,6 +102,8 @@ def basic_mail
   post 'users'    => 'application#create'
   get 'new'       => 'application#new'
   put 'users/:id' => 'application#update'
+
+  get 'attach_context' => 'application#attach_context'
 end
 
 Dummy.initialize!
diff --git a/spec/fixtures/rails50.rb b/spec/fixtures/rails50.rb
index 1fae3cb..da03f27 100644
--- a/spec/fixtures/rails50.rb
+++ b/spec/fixtures/rails50.rb
@@ -49,6 +49,12 @@ def update
     @id = params[:id]
     render '/user'
   end
+
+  def attach_context
+    Loga.attach_context(animal: 'monkey')
+
+    render json: { hello: :world }
+  end
 end
 
 class FakeMailer < ActionMailer::Base
@@ -68,6 +74,27 @@ def basic_mail
   end
 end
 
+class FakeMailerWithContext < ActionMailer::Base
+  default from: 'notifications@example.com'
+
+  def self.send_email
+    Loga.attach_context(tshirt_size: 'XL')
+    Loga.attach_context(height: 155)
+    Loga.attach_context(weight: 122)
+
+    basic_mail.deliver_now
+  end
+
+  def basic_mail
+    mail(
+      to: 'user@example.com',
+      subject: 'Welcome to My Awesome Site',
+      body: 'Banana muffin',
+      content_type: 'text/html',
+    )
+  end
+end
+
 Dummy.routes.append do
   get 'ok'        => 'application#ok'
   get 'error'     => 'application#error'
@@ -75,6 +102,8 @@ def basic_mail
   post 'users'    => 'application#create'
   get 'new'       => 'application#new'
   put 'users/:id' => 'application#update'
+
+  get 'attach_context' => 'application#attach_context'
 end
 
 Dummy.initialize!
diff --git a/spec/fixtures/rails52.rb b/spec/fixtures/rails52.rb
index 9c5ddf1..ea244a3 100644
--- a/spec/fixtures/rails52.rb
+++ b/spec/fixtures/rails52.rb
@@ -49,6 +49,12 @@ def update
     @id = params[:id]
     render '/user'
   end
+
+  def attach_context
+    Loga.attach_context(animal: 'monkey')
+
+    render json: { hello: :world }
+  end
 end
 
 class FakeMailer < ActionMailer::Base
@@ -68,6 +74,27 @@ def basic_mail
   end
 end
 
+class FakeMailerWithContext < ActionMailer::Base
+  default from: 'notifications@example.com'
+
+  def self.send_email
+    Loga.attach_context(tshirt_size: 'XL')
+    Loga.attach_context(height: 155)
+    Loga.attach_context(weight: 122)
+
+    basic_mail.deliver_now
+  end
+
+  def basic_mail
+    mail(
+      to: 'user@example.com',
+      subject: 'Welcome to My Awesome Site',
+      body: 'Banana muffin',
+      content_type: 'text/html',
+    )
+  end
+end
+
 Dummy.routes.append do
   get 'ok'        => 'application#ok'
   get 'error'     => 'application#error'
@@ -75,6 +102,8 @@ def basic_mail
   post 'users'    => 'application#create'
   get 'new'       => 'application#new'
   put 'users/:id' => 'application#update'
+
+  get 'attach_context' => 'application#attach_context'
 end
 
 Dummy.initialize!
diff --git a/spec/integration/rails/action_mailer_spec.rb b/spec/integration/rails/action_mailer_spec.rb
index 47f1ceb..4ca419c 100644
--- a/spec/integration/rails/action_mailer_spec.rb
+++ b/spec/integration/rails/action_mailer_spec.rb
@@ -59,5 +59,17 @@
 
       expect(last_log_entry).to have_key('_unique_id')
     end
+
+    it 'attaches custom context' do
+      FakeMailerWithContext.send_email
+
+      expected_context = {
+        '_tshirt_size' => 'XL',
+        '_height' => 155,
+        '_weight' => 122,
+      }
+
+      expect(last_log_entry).to include(expected_context)
+    end
   end
 end
diff --git a/spec/integration/rails/request_spec.rb b/spec/integration/rails/request_spec.rb
index 9e6f338..7c1c727 100644
--- a/spec/integration/rails/request_spec.rb
+++ b/spec/integration/rails/request_spec.rb
@@ -6,12 +6,14 @@
 
   let(:log_entries) do
     entries = []
+
     STREAM.tap do |s|
       s.rewind
       entries = s.read.split("\n").map { |line| JSON.parse(line) }
       s.close
       s.reopen
     end
+
     entries
   end
 
@@ -22,43 +24,56 @@
 
   it 'preserves rails parameters' do
     get '/show'
+
     expect(json_response).to eq('action' => 'show', 'controller' => 'application')
   end
 
   it 'includes the controller name and action' do
     get '/ok'
+
     expect(last_log_entry).to include('_request.controller' => 'ApplicationController#ok')
   end
 
-  describe 'LogSubscriber' do
-    describe 'ActionController' do
-      let(:action_controller_notifications) do
-        log_entries.select { |e| e.to_json =~ /Processing by|Completed/ }
-      end
+  describe 'ActionController::LogSubscriber' do
+    let(:action_controller_notifications) do
+      log_entries.select { |e| e.to_json =~ /Processing by|Completed/ }
+    end
 
-      it 'silences ActionController::LogSubscriber' do
-        get '/show'
-        expect(action_controller_notifications).to be_empty
-      end
+    it 'silences ActionController::LogSubscriber' do
+      get '/show'
+
+      expect(action_controller_notifications).to be_empty
     end
+  end
 
-    describe 'ActionView' do
-      let(:action_view_notifications) do
-        log_entries.select { |e| e.to_json =~ /Rendered/ }
-      end
+  describe 'ActionView::LogSubscriber' do
+    let(:action_view_notifications) do
+      log_entries.select { |e| e.to_json =~ /Rendered/ }
+    end
 
-      it 'silences ActionView::LogSubscriber' do
-        put '/users/5'
-        expect(action_view_notifications).to be_empty
-      end
+    it 'silences ActionView::LogSubscriber' do
+      put '/users/5'
+
+      expect(action_view_notifications).to be_empty
     end
   end
 
-  describe 'when request causes ActionDispatch 404' do
+  context 'when request causes ActionDispatch 404' do
     it 'does not log ActionDispatch::DebugExceptions' do
       get '/not_found', {}, 'HTTP_X_REQUEST_ID' => '471a34dc'
-      expect(log_entries.count).to eq(1)
-      expect(last_log_entry['short_message']).to eq('GET /not_found 404 in 0ms')
+
+      aggregate_failures do
+        expect(log_entries.count).to eq(1)
+        expect(last_log_entry['short_message']).to eq('GET /not_found 404 in 0ms')
+      end
+    end
+  end
+
+  context 'when custom context is attached' do
+    it 'adds context to the log' do
+      get '/attach_context'
+
+      expect(last_log_entry['_animal']).to eq 'monkey'
     end
   end
 end
diff --git a/spec/integration/sidekiq_spec.rb b/spec/integration/sidekiq_spec.rb
index 62f83b5..aebf33b 100644
--- a/spec/integration/sidekiq_spec.rb
+++ b/spec/integration/sidekiq_spec.rb
@@ -12,10 +12,20 @@
   config.redis = dummy_redis_config
 end
 
-class MySidekiqWorker
-  include Sidekiq::Worker
+module Loga
+  class MySidekiqWorker
+    include ::Sidekiq::Worker
 
-  def perform(_name); end
+    def perform(_name); end
+  end
+
+  class DummyWorkerWithContext
+    include ::Sidekiq::Worker
+
+    def perform(name)
+      Loga.attach_context(name_upcased: name.upcase)
+    end
+  end
 end
 
 describe 'Sidekiq client logger' do
@@ -54,12 +64,12 @@ def perform(_name); end
   end
 
   it 'pushes a new element in the default queue' do
-    MySidekiqWorker.perform_async('Bob')
+    Loga::MySidekiqWorker.perform_async('Bob')
 
     last_element = JSON.parse(Redis.current.lpop('queue:default'))
 
     aggregate_failures do
-      expect(last_element['class']).to eq 'MySidekiqWorker'
+      expect(last_element['class']).to eq 'Loga::MySidekiqWorker'
       expect(last_element['args']).to eq ['Bob']
       expect(last_element['retry']).to eq true
       expect(last_element['queue']).to eq 'default'
@@ -98,7 +108,7 @@ def options
     end
 
     it 'logs the job processing event' do
-      MySidekiqWorker.perform_async('Bob')
+      Loga::MySidekiqWorker.perform_async('Bob')
 
       require 'sidekiq/processor'
       Sidekiq::Processor.new(mgr.new).start
@@ -108,7 +118,7 @@ def options
         '_queue'=> 'default',
         '_retry'=> true,
         '_params'=> ['Bob'],
-        '_class'=> 'MySidekiqWorker',
+        '_class'=> 'Loga::MySidekiqWorker',
         '_type'=> 'sidekiq',
         '_service.name'=> 'hello_world_app',
         '_service.version'=> '1.0',
@@ -124,8 +134,18 @@ def options
           expect(json_line).to have_key(key)
         end
 
-        expect(json_line['short_message']).to match(/MySidekiqWorker with jid:*/)
+        expect(json_line['short_message']).to match(/Loga::MySidekiqWorker with jid:*/)
       end
     end
+
+    it 'attaches a custom context' do
+      Loga::DummyWorkerWithContext.perform_async('John Doe')
+
+      require 'sidekiq/processor'
+      Sidekiq::Processor.new(mgr.new).start
+      sleep 0.5
+
+      expect(json_line['_name_upcased']).to eq 'JOHN DOE'
+    end
   end
 end
diff --git a/spec/integration/sinatra_spec.rb b/spec/integration/sinatra_spec.rb
index d304565..44ea015 100644
--- a/spec/integration/sinatra_spec.rb
+++ b/spec/integration/sinatra_spec.rb
@@ -1,6 +1,6 @@
 require 'spec_helper'
 
-class MySinatraApp < Sinatra::Base
+Loga::MySinatraApp = Class.new(Sinatra::Base) do
   set :logging, false
 
   get '/ok' do
@@ -19,27 +19,35 @@ class MySinatraApp < Sinatra::Base
   get '/new' do
     redirect '/ok'
   end
+
+  get '/attach_context' do
+    Loga.attach_context(fruit: 'banana')
+
+    'I am a banana'
+  end
 end
 
 RSpec.describe 'Structured logging with Sinatra', :with_hostname, :timecop do
-  let(:io) { StringIO.new }
-  let(:format) {}
+  let(:device) { StringIO.new }
+
   let(:last_log_entry) do
-    io.rewind
-    JSON.parse(io.read)
+    device.rewind
+    JSON.parse(device.read)
   end
+
   let(:app) do
     Rack::Builder.new do
       use Loga::Rack::RequestId
       use Loga::Rack::Logger
-      run MySinatraApp
+      run Loga::MySinatraApp
     end
   end
 
   before do
     Loga.reset
+
     Loga.configure(
-      device: io,
+      device: device,
       filter_parameters: [:password],
       format: format,
       service_name: 'hello_world_app',
@@ -48,80 +56,113 @@ class MySinatraApp < Sinatra::Base
     )
   end
 
-  context 'when RACK_ENV is production', if: ENV['RACK_ENV'].eql?('production') do
+  describe 'RACK_ENV is production', if: ENV['RACK_ENV'].eql?('production') do
     let(:format) { :gelf }
 
     include_examples 'request logger'
 
+    it 'attaches a custom context' do
+      get '/attach_context'
+
+      expect(last_log_entry['_fruit']).to eq 'banana'
+    end
+
     it 'does not include the controller name and action' do
       get '/ok'
+
       expect(last_log_entry).not_to include('_request.controller')
     end
   end
 
-  # rubocop:disable Metrics/LineLength
-  context 'when RACK_ENV is development', if: ENV['RACK_ENV'].eql?('development') do
+  describe 'RACK_ENV is development', if: ENV['RACK_ENV'].eql?('development') do
     let(:format) { :simple }
+
     let(:last_log_entry) do
-      io.rewind
-      io.read
-    end
-    let(:data) do
-      {
-        'status' => 200,
-        'method' => 'GET',
-        'path'   => '/ok',
-        'params' => { 'username'=>'yoshi' },
-        'request_id' => '700a6a01',
-        'request_ip' => '127.0.0.1',
-        'user_agent' => nil,
-        'duration'   => 0,
-      }
+      device.rewind
+      device.read
     end
-    let(:data_as_text)  { "data=#{{ request: data }.inspect}" }
+
     let(:time_pid_tags) { '[2015-12-15T09:30:05.123000+06:00 #999][700a6a01 TEST_TAG]' }
 
-    before do
-      allow(Process).to receive(:pid).and_return(999)
-    end
+    before { allow(Process).to receive(:pid).and_return(999) }
+
+    context 'when request responds with HTTP status 200' do
+      let(:data) do
+        {
+          request: {
+            'status' => 200,
+            'method' => 'GET',
+            'path'   => '/ok',
+            'params' => { 'username'=>'yoshi' },
+            'request_id' => '700a6a01',
+            'request_ip' => '127.0.0.1',
+            'user_agent' => nil,
+            'duration'   => 0,
+          },
+        }
+      end
 
-    describe 'get request' do
       it 'logs the request' do
         get '/ok', { username: 'yoshi' }, 'HTTP_X_REQUEST_ID' => '700a6a01'
 
-        expect(last_log_entry).to eq("I, #{time_pid_tags} GET /ok?username=yoshi 200 in 0ms type=request #{data_as_text}\n")
+        result = "I, #{time_pid_tags} GET /ok?username=yoshi "\
+                 "200 in 0ms type=request data=#{data.inspect}\n"
+
+        expect(last_log_entry).to eq(result)
       end
     end
 
-    describe 'request with redirect' do
+    context 'when request responds with HTTP status 302' do
       let(:data) do
-        super().merge(
-          'status' => 302,
-          'path'   => '/new',
-          'params' => {},
-        )
+        {
+          request: {
+            'status' => 302,
+            'method' => 'GET',
+            'path'   => '/new',
+            'params' => {},
+            'request_id' => '700a6a01',
+            'request_ip' => '127.0.0.1',
+            'user_agent' => nil,
+            'duration'   => 0,
+          },
+        }
       end
 
-      it 'specifies the original path' do
+      it 'logs the request' do
         get '/new', {}, 'HTTP_X_REQUEST_ID' => '700a6a01'
-        expect(last_log_entry).to eql("I, #{time_pid_tags} GET /new 302 in 0ms type=request #{data_as_text}\n")
+
+        result = "I, #{time_pid_tags} GET /new 302 "\
+                 "in 0ms type=request data=#{data.inspect}\n"
+
+        expect(last_log_entry).to eql(result)
       end
     end
 
-    context 'when the request raises an exception' do
+    context 'when the request responds with HTTP status 500' do
       let(:data) do
-        super().merge(
-          'status' => 500,
-          'path'   => '/error',
-          'params' => {},
-        )
+        {
+          request: {
+            'status' => 500,
+            'method' => 'GET',
+            'path'   => '/error',
+            'params' => {},
+            'request_id' => '700a6a01',
+            'request_ip' => '127.0.0.1',
+            'user_agent' => nil,
+            'duration'   => 0,
+          },
+        }
       end
 
-      it 'logs the request with the exception' do
+      it 'logs the request' do
         get '/error', {}, 'HTTP_X_REQUEST_ID' => '700a6a01'
-        expect(last_log_entry).to eql("E, #{time_pid_tags} GET /error 500 in 0ms type=request #{data_as_text} exception=undefined method `name' for nil:NilClass\n")
+
+        result = "E, #{time_pid_tags} GET /error 500 "\
+                 "in 0ms type=request data=#{data.inspect} "\
+                 "exception=undefined method `name' for nil:NilClass\n"
+
+        expect(last_log_entry).to eql(result)
       end
     end
   end
-  # rubocop:enable Metrics/LineLength
 end
diff --git a/spec/loga/context_manager_spec.rb b/spec/loga/context_manager_spec.rb
new file mode 100644
index 0000000..641de40
--- /dev/null
+++ b/spec/loga/context_manager_spec.rb
@@ -0,0 +1,37 @@
+require 'spec_helper'
+
+RSpec.describe Loga::ContextManager do
+  subject(:manager) { described_class.new }
+
+  describe '.current' do
+    it 'returns an instance of context manager' do
+      expect(described_class.current).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#clear' do
+    it 'sets the value of @context to nil' do
+      manager.clear
+
+      expect(manager.instance_variable_get(:@context)).to eq({})
+    end
+  end
+
+  describe '#attach_context' do
+    it 'adds the given custom attributes to @context' do
+      attach_action = -> { manager.attach_context(uuid: 'lorem-ipsum') }
+
+      expect(&attach_action).to change { manager.instance_variable_get(:@context) }
+        .from({})
+        .to(uuid: 'lorem-ipsum')
+    end
+  end
+
+  describe '#retrieve_context' do
+    it 'can retrieve context' do
+      manager.attach_context(fruit: 'banana')
+
+      expect(manager.retrieve_context).to eq(fruit: 'banana')
+    end
+  end
+end