diff --git a/serverside_challenge_2/challenge/.rspec b/serverside_challenge_2/challenge/.rspec
new file mode 100644
index 000000000..c99d2e739
--- /dev/null
+++ b/serverside_challenge_2/challenge/.rspec
@@ -0,0 +1 @@
+--require spec_helper
diff --git a/serverside_challenge_2/challenge/.rubocop.yml b/serverside_challenge_2/challenge/.rubocop.yml
new file mode 100644
index 000000000..db1c23f63
--- /dev/null
+++ b/serverside_challenge_2/challenge/.rubocop.yml
@@ -0,0 +1,10 @@
+Documentation:
+  Enabled: false
+MethodLength:
+  CountComments: true 
+  Max: 25 
+  Style/FrozenStringLiteralComment:
+  Enabled: false
+Metrics:
+  Enabled: false
+  
\ No newline at end of file
diff --git a/serverside_challenge_2/challenge/Gemfile b/serverside_challenge_2/challenge/Gemfile
index 43bf67fe3..a12bf9c7d 100644
--- a/serverside_challenge_2/challenge/Gemfile
+++ b/serverside_challenge_2/challenge/Gemfile
@@ -36,9 +36,12 @@ gem "bootsnap", require: false
 # Use Rack CORS for handling Cross-Origin Resource Sharing (CORS), making cross-origin AJAX possible
 # gem "rack-cors"
 
+gem 'rubocop-rails', '~> 2.32'
+
 group :development, :test do
   # See https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debug-gem
   gem "debug", platforms: %i[ mri mingw x64_mingw ]
+  gem 'rspec-rails'
 end
 
 group :development do
diff --git a/serverside_challenge_2/challenge/Gemfile.lock b/serverside_challenge_2/challenge/Gemfile.lock
index a47fb85f5..d6148432f 100644
--- a/serverside_challenge_2/challenge/Gemfile.lock
+++ b/serverside_challenge_2/challenge/Gemfile.lock
@@ -66,6 +66,7 @@ GEM
       i18n (>= 1.6, < 2)
       minitest (>= 5.1)
       tzinfo (~> 2.0)
+    ast (2.4.3)
     bootsnap (1.18.3)
       msgpack (~> 1.2)
     builder (3.2.4)
@@ -75,6 +76,7 @@ GEM
     debug (1.9.1)
       irb (~> 1.10)
       reline (>= 0.3.8)
+    diff-lcs (1.6.2)
     erubi (1.12.0)
     globalid (1.2.1)
       activesupport (>= 6.1)
@@ -84,6 +86,9 @@ GEM
     irb (1.11.2)
       rdoc
       reline (>= 0.4.2)
+    json (2.13.0)
+    language_server-protocol (3.17.0.5)
+    lint_roller (1.1.0)
     loofah (2.22.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
@@ -111,7 +116,12 @@ GEM
       racc (~> 1.4)
     nokogiri (1.16.2-x86_64-linux)
       racc (~> 1.4)
+    parallel (1.27.0)
+    parser (3.3.8.0)
+      ast (~> 2.4.1)
+      racc
     pg (1.5.4)
+    prism (1.4.0)
     psych (5.1.2)
       stringio
     puma (5.6.8)
@@ -148,16 +158,59 @@ GEM
       rake (>= 12.2)
       thor (~> 1.0)
       zeitwerk (~> 2.5)
+    rainbow (3.1.1)
     rake (13.1.0)
     rdoc (6.6.2)
       psych (>= 4.0.0)
+    regexp_parser (2.10.0)
     reline (0.4.2)
       io-console (~> 0.5)
+    rspec-core (3.13.5)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.5)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.5)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-rails (7.1.1)
+      actionpack (>= 7.0)
+      activesupport (>= 7.0)
+      railties (>= 7.0)
+      rspec-core (~> 3.13)
+      rspec-expectations (~> 3.13)
+      rspec-mocks (~> 3.13)
+      rspec-support (~> 3.13)
+    rspec-support (3.13.4)
+    rubocop (1.78.0)
+      json (~> 2.3)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.1.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 2.9.3, < 3.0)
+      rubocop-ast (>= 1.45.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 4.0)
+    rubocop-ast (1.46.0)
+      parser (>= 3.3.7.2)
+      prism (~> 1.4)
+    rubocop-rails (2.32.0)
+      activesupport (>= 4.2.0)
+      lint_roller (~> 1.1)
+      rack (>= 1.1)
+      rubocop (>= 1.75.0, < 2.0)
+      rubocop-ast (>= 1.44.0, < 2.0)
+    ruby-progressbar (1.13.0)
     stringio (3.1.0)
     thor (1.3.0)
     timeout (0.4.1)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
+    unicode-display_width (3.1.4)
+      unicode-emoji (~> 4.0, >= 4.0.4)
+    unicode-emoji (4.0.4)
     websocket-driver (0.7.6)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
@@ -173,6 +226,8 @@ DEPENDENCIES
   pg (~> 1.1)
   puma (~> 5.0)
   rails (~> 7.0.8)
+  rspec-rails
+  rubocop-rails (~> 2.32)
   tzinfo-data
 
 RUBY VERSION
diff --git a/serverside_challenge_2/challenge/app/controllers/api/v1/power_supply_plan_controller.rb b/serverside_challenge_2/challenge/app/controllers/api/v1/power_supply_plan_controller.rb
new file mode 100644
index 000000000..294345c2c
--- /dev/null
+++ b/serverside_challenge_2/challenge/app/controllers/api/v1/power_supply_plan_controller.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Api
+  module V1
+    class PowerSupplyPlanController < ApplicationController
+      def simulate_all
+        simulator = PowerSupplyPlanSimulator.new(params[:amp], params[:meter_rate])
+        result = simulator.call
+
+        return render json: [result] if result.is_a?(Hash) && result.key?(:error)
+
+        render json: result
+      end
+    end
+  end
+end
diff --git a/serverside_challenge_2/challenge/app/models/basic_charge.rb b/serverside_challenge_2/challenge/app/models/basic_charge.rb
new file mode 100644
index 000000000..a7c0f9e58
--- /dev/null
+++ b/serverside_challenge_2/challenge/app/models/basic_charge.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class BasicCharge < ApplicationRecord
+  belongs_to :power_supply_plan
+end
diff --git a/serverside_challenge_2/challenge/app/models/meter_rate_charge.rb b/serverside_challenge_2/challenge/app/models/meter_rate_charge.rb
new file mode 100644
index 000000000..2b932e845
--- /dev/null
+++ b/serverside_challenge_2/challenge/app/models/meter_rate_charge.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class MeterRateCharge < ApplicationRecord
+  belongs_to :power_supply_plan
+
+  def calculate_charge(meter_rate)
+    min_rate = min_meter_rate
+    max_rate = max_meter_rate
+    step_price = price
+    return 0 if min_rate > meter_rate
+
+    if max_rate.nil?
+      return step_price * meter_rate if min_rate.zero?
+
+      return step_price * (meter_rate - min_rate + 1)
+    end
+    if max_rate.to_i < meter_rate.to_i
+      return step_price * (max_rate - min_rate) if min_rate.zero?
+
+      step_price * (max_rate - min_rate + 1)
+    else
+      return step_price * (meter_rate - min_rate) if min_rate.zero?
+
+      step_price * (meter_rate - min_rate + 1)
+    end
+  end
+end
diff --git a/serverside_challenge_2/challenge/app/models/power_supply_plan.rb b/serverside_challenge_2/challenge/app/models/power_supply_plan.rb
new file mode 100644
index 000000000..5bbb3f71b
--- /dev/null
+++ b/serverside_challenge_2/challenge/app/models/power_supply_plan.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class PowerSupplyPlan < ApplicationRecord
+  belongs_to :provider
+  has_many :meter_rate_charges
+  has_many :basic_charges
+
+  def calculate_total_amount(amp, meter_rate)
+    basic_charge_record = basic_charges.where(amp: amp)
+    return nil if basic_charge_record.blank?
+
+    basic_charge_amount = basic_charge_record.first.price.to_f
+    meter_rate_charge_amount = calculate_meter_rate_charge(meter_rate)
+    (basic_charge_amount + meter_rate_charge_amount).floor(0).to_i
+  end
+
+  def calculate_meter_rate_charge(meter_rate)
+    total_meter_rate_charges = 0
+
+    meter_rate_charges.each do |step|
+      total_meter_rate_charges += step.calculate_charge(meter_rate.to_i)
+    end
+    total_meter_rate_charges
+  end
+end
diff --git a/serverside_challenge_2/challenge/app/models/provider.rb b/serverside_challenge_2/challenge/app/models/provider.rb
new file mode 100644
index 000000000..445f24073
--- /dev/null
+++ b/serverside_challenge_2/challenge/app/models/provider.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class Provider < ApplicationRecord
+  has_many :power_supply_plans
+end
diff --git a/serverside_challenge_2/challenge/app/services/power_supply_plan_simulator.rb b/serverside_challenge_2/challenge/app/services/power_supply_plan_simulator.rb
new file mode 100644
index 000000000..f990e9430
--- /dev/null
+++ b/serverside_challenge_2/challenge/app/services/power_supply_plan_simulator.rb
@@ -0,0 +1,60 @@
+class PowerSupplyPlanSimulator
+  VALID_AMPS = [10, 15, 20, 30, 40, 50, 60].freeze
+
+  def initialize(amp, meter_rate)
+    @amp = amp
+    @meter_rate = meter_rate
+    @errors = []
+  end
+
+  def call
+    unless validate_params
+      return {
+        error: {
+          code: 400,
+          message: @errors.join('\n')
+        }
+      }
+    end
+
+    result = []
+    PowerSupplyPlan.includes(:provider, :meter_rate_charges, :basic_charges).each do |plan|
+      calculate_result = plan.calculate_total_amount(@amp, @meter_rate)
+      next unless calculate_result
+
+      result << {
+        "provider_name": plan.provider.name,
+        "plan_name": plan.name,
+        "price": calculate_result
+      }
+    end
+    result
+  end
+
+  def validate_params
+    if @amp.blank?
+      @errors << "リクエストパラメータ 'amp' が不足しています。"
+    else
+      @errors << "リクエストパラメータ 'amp' の値が不正です。'10 / 15 / 20 / 30 / 40 / 50 / 60' のいずれかの値を指定してください。" unless valid_amp?(@amp)
+    end
+    if @meter_rate.blank?
+      @errors << "リクエストパラメータ 'meter_rate' が不足しています。"
+    else
+      unless numeric?(@meter_rate) && @meter_rate.to_i >= 0
+        @errors << "リクエストパラメータ 'meter_rate' の値が不正です。0以上の整数を指定してください。"
+      end
+    end
+    @errors.blank?
+  end
+
+  def numeric?(string)
+    Integer(string)
+    true
+  rescue ArgumentError, TypeError
+    false
+  end
+
+  def valid_amp?(amp)
+    VALID_AMPS.include?(amp.to_i)
+  end
+end
diff --git a/serverside_challenge_2/challenge/config/credentials.yml.enc b/serverside_challenge_2/challenge/config/credentials.yml.enc
index 57c5aee24..3530d435b 100644
--- a/serverside_challenge_2/challenge/config/credentials.yml.enc
+++ b/serverside_challenge_2/challenge/config/credentials.yml.enc
@@ -1 +1 @@
-bZE5VzGsIQoeBEOa79I28cq/Ax0SuIaPhy5+NFktLVZLNGpuzqmkTkAiWc+arbGUDU8aaedg9zUvnBBc0dPrATeWISHtFxVwJMScZQeSW1k7BUgSD6B6YsewlgtpEDFDAXoGZEQoTbM2FY3lDCd0dZF7I1+DsB4I9Z5NamOgOlNEK8gMQD3p3Csqc/mVhmdI3PjBEmblvTjkZIVOdfX1CmqJ/RZm1Lxu3RdNMaiXiOZL7I+oXE1SFfjWm7+CTwb+Vfs6nGMviDHDKh9k3jyb7Vflpx/frY4vYzP8WMzgbJPX4UHmxa7qS51tJ1ECpK265nS1mLsqxL7wRbjyzfUNtXknSSopGD7sDDm7F9ta8/e1nzU79uTH1LKFpWQWGMSbXmSu4EKPu655BA9ckdwnSsf67RYNX7/Nw5pp--9AT1V0z/SBAdVTZ5--JK/4x776vcnN7qGZuylM0g==
\ No newline at end of file
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--97QWVDZ45R2Bjr3G--byi/t6soITzi5vJv5PEsvw==
\ No newline at end of file
diff --git a/serverside_challenge_2/challenge/config/routes.rb b/serverside_challenge_2/challenge/config/routes.rb
index 262ffd547..e73a37fdf 100644
--- a/serverside_challenge_2/challenge/config/routes.rb
+++ b/serverside_challenge_2/challenge/config/routes.rb
@@ -3,4 +3,9 @@
 
   # Defines the root path route ("/")
   # root "articles#index"
+  namespace :api do
+    namespace :v1 do
+      get "simulate_all_plan", to: "power_supply_plan#simulate_all"
+    end
+  end
 end
diff --git a/serverside_challenge_2/challenge/db/migrate/20250723134304_create_basic_charges.rb b/serverside_challenge_2/challenge/db/migrate/20250723134304_create_basic_charges.rb
new file mode 100644
index 000000000..8b9371f43
--- /dev/null
+++ b/serverside_challenge_2/challenge/db/migrate/20250723134304_create_basic_charges.rb
@@ -0,0 +1,34 @@
+class CreateBasicCharges < ActiveRecord::Migration[7.0]
+  def change
+    create_table :providers do |t|
+      t.string :provider_name, :null => false
+      t.string :rounding_amount_method, :null => false
+
+      t.timestamps
+    end
+
+    create_table :power_supply_plans do |t|
+      t.belongs_to :provider
+      t.string :plan_name, :null => false
+
+      t.timestamps
+    end
+    
+    create_table :meter_rate_charges do |t|
+      t.belongs_to :power_supply_plan
+      t.integer :min_meter_rate, :null => false
+      t.integer :max_meter_rate
+      t.decimal :price, precision: 6, scale: 2, :null => false
+
+      t.timestamps
+    end
+
+    create_table :basic_charges do |t|
+      t.belongs_to :power_supply_plan 
+      t.integer :amp, :null => false
+      t.decimal :price, precision: 6, scale: 2, :null => false
+
+      t.timestamps
+    end
+  end
+end
diff --git a/serverside_challenge_2/challenge/db/migrate/20250726103216_remove_rounding_amount_method_from_provider.rb b/serverside_challenge_2/challenge/db/migrate/20250726103216_remove_rounding_amount_method_from_provider.rb
new file mode 100644
index 000000000..d9d065ba2
--- /dev/null
+++ b/serverside_challenge_2/challenge/db/migrate/20250726103216_remove_rounding_amount_method_from_provider.rb
@@ -0,0 +1,9 @@
+class RemoveRoundingAmountMethodFromProvider < ActiveRecord::Migration[7.0]
+  def up
+    remove_column :providers, :rounding_amount_method, :string
+  end
+
+  def down
+    add_column :providers, :rounding_amount_method, :string
+  end
+end
\ No newline at end of file
diff --git a/serverside_challenge_2/challenge/db/migrate/20250726111141_rename_provider_name_column_to_name.rb b/serverside_challenge_2/challenge/db/migrate/20250726111141_rename_provider_name_column_to_name.rb
new file mode 100644
index 000000000..4f338026f
--- /dev/null
+++ b/serverside_challenge_2/challenge/db/migrate/20250726111141_rename_provider_name_column_to_name.rb
@@ -0,0 +1,5 @@
+class RenameProviderNameColumnToName < ActiveRecord::Migration[7.0]
+  def change
+    rename_column :providers, :provider_name, :name
+  end
+end
diff --git a/serverside_challenge_2/challenge/db/migrate/20250726111346_rename_plan__name_column_to_name.rb b/serverside_challenge_2/challenge/db/migrate/20250726111346_rename_plan__name_column_to_name.rb
new file mode 100644
index 000000000..2bd08e0d5
--- /dev/null
+++ b/serverside_challenge_2/challenge/db/migrate/20250726111346_rename_plan__name_column_to_name.rb
@@ -0,0 +1,5 @@
+class RenamePlanNameColumnToName < ActiveRecord::Migration[7.0]
+  def change
+        rename_column :power_supply_plans, :plan_name, :name
+  end
+end
diff --git a/serverside_challenge_2/challenge/db/schema.rb b/serverside_challenge_2/challenge/db/schema.rb
new file mode 100644
index 000000000..ee18ba699
--- /dev/null
+++ b/serverside_challenge_2/challenge/db/schema.rb
@@ -0,0 +1,50 @@
+# This file is auto-generated from the current state of the database. Instead
+# of editing this file, please use the migrations feature of Active Record to
+# incrementally modify your database, and then regenerate this schema definition.
+#
+# This file is the source Rails uses to define your schema when running `bin/rails
+# db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
+# be faster and is potentially less error prone than running all of your
+# migrations from scratch. Old migrations may fail to apply correctly if those
+# migrations use external dependencies or application code.
+#
+# It's strongly recommended that you check this file into your version control system.
+
+ActiveRecord::Schema[7.0].define(version: 2025_07_26_111346) do
+  # These are extensions that must be enabled in order to support this database
+  enable_extension "plpgsql"
+
+  create_table "basic_charges", force: :cascade do |t|
+    t.bigint "power_supply_plan_id"
+    t.integer "amp", null: false
+    t.decimal "price", precision: 6, scale: 2, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["power_supply_plan_id"], name: "index_basic_charges_on_power_supply_plan_id"
+  end
+
+  create_table "meter_rate_charges", force: :cascade do |t|
+    t.bigint "power_supply_plan_id"
+    t.integer "min_meter_rate", null: false
+    t.integer "max_meter_rate"
+    t.decimal "price", precision: 6, scale: 2, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["power_supply_plan_id"], name: "index_meter_rate_charges_on_power_supply_plan_id"
+  end
+
+  create_table "power_supply_plans", force: :cascade do |t|
+    t.bigint "provider_id"
+    t.string "name", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["provider_id"], name: "index_power_supply_plans_on_provider_id"
+  end
+
+  create_table "providers", force: :cascade do |t|
+    t.string "name", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+  end
+
+end
diff --git a/serverside_challenge_2/challenge/db/seeds.rb b/serverside_challenge_2/challenge/db/seeds.rb
index bc25fce30..5b2bbf57e 100644
--- a/serverside_challenge_2/challenge/db/seeds.rb
+++ b/serverside_challenge_2/challenge/db/seeds.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This file should contain all the record creation needed to seed the database with its default values.
 # The data can then be loaded with the bin/rails db:seed command (or created alongside the database with db:setup).
 #
@@ -5,3 +7,99 @@
 #
 #   movies = Movie.create([{ name: "Star Wars" }, { name: "Lord of the Rings" }])
 #   Character.create(name: "Luke", movie: movies.first)
+
+p '==================== provider create ===================='
+
+Provider.create!(
+  [
+    { name: '東京電力エナジーパートナー' },
+    { name: '東京ガス' },
+    { name: 'Looopでんき' }
+  ]
+)
+
+p '==================== power_supply_plan create ===================='
+
+provider = Provider.find(1)
+plans = provider.power_supply_plans.new(
+  [
+    { name: '従量電灯B' },
+    { name: 'スタンダードS' }
+  ]
+)
+plans.each(&:save)
+
+Provider.find(2).power_supply_plans.create!(name: 'ずっとも電気1')
+Provider.find(3).power_supply_plans.create!(name: 'おうちプラン')
+
+p '==================== basic_charge create ===================='
+
+seed_data = [
+  { index: 1, data: [
+    { amp: 10, price: 286.00 },
+    { amp: 15, price: 429.00 },
+    { amp: 20, price: 572.00 },
+    { amp: 30, price: 858.00 },
+    { amp: 40, price: 1144.00 },
+    { amp: 50, price: 1430.00 },
+    { amp: 60, price: 1716.00 }
+  ] },
+  { index: 2, data: [
+    { amp: 10, price: 311.75 },
+    { amp: 15, price: 467.63 },
+    { amp: 20, price: 623.50 },
+    { amp: 30, price: 935.25 },
+    { amp: 40, price: 1247.00 },
+    { amp: 50, price: 1558.75 },
+    { amp: 60, price: 1870.50 }
+  ] },
+  { index: 3, data: [
+    { amp: 30, price: 858.00 },
+    { amp: 40, price: 1144.00 },
+    { amp: 50, price: 1430.00 },
+    { amp: 60, price: 1716.00 }
+  ] },
+  { index: 4, data: [
+    { amp: 10, price: 0.00 },
+    { amp: 15, price: 0.00 },
+    { amp: 20, price: 0.00 },
+    { amp: 30, price: 0.00 },
+    { amp: 40, price: 0.00 },
+    { amp: 50, price: 0.00 },
+    { amp: 60, price: 0.00 }
+  ] }
+]
+seed_data.each do |d|
+  plan = PowerSupplyPlan.find(d[:index])
+  basic_charges = plan.basic_charges.new(d[:data])
+  basic_charges.each(&:save)
+end
+
+p '==================== meter_ratecharge create ===================='
+
+seed_data = [
+  { index: 1, data: [
+    { min_meter_rate: 0, max_meter_rate: 120, price: 19.88 },
+    { min_meter_rate: 121, max_meter_rate: 300, price: 26.48 },
+    { min_meter_rate: 301, max_meter_rate: nil, price: 30.57 }
+  ] },
+  { index: 2, data: [
+    { min_meter_rate: 0, max_meter_rate: 120, price: 29.80 },
+    { min_meter_rate: 121, max_meter_rate: 300, price: 36.40 },
+    { min_meter_rate: 301, max_meter_rate: nil, price: 40.49 }
+  ] },
+  { index: 3, data: [
+    { min_meter_rate: 0, max_meter_rate: 140, price: 23.67 },
+    { min_meter_rate: 141, max_meter_rate: 350, price: 23.88 },
+    { min_meter_rate: 351, max_meter_rate: nil, price: 26.41 }
+  ] },
+  { index: 4, data: [
+    { min_meter_rate: 0, max_meter_rate: nil, price: 28.80 }
+  ] }
+]
+
+seed_data.each do |d|
+  plan = PowerSupplyPlan.find(d[:index])
+  basic_charges = plan.meter_rate_charges.new(d[:data])
+  basic_charges.each(&:save)
+end
diff --git a/serverside_challenge_2/challenge/spec/models/meter_rate_charge.rb b/serverside_challenge_2/challenge/spec/models/meter_rate_charge.rb
new file mode 100644
index 000000000..a5a346831
--- /dev/null
+++ b/serverside_challenge_2/challenge/spec/models/meter_rate_charge.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe PowerSupplyPlan, type: :model do
+  let!(:provider1) { Provider.create!(id: 1, name: '東京ガス') }
+  let!(:provider2) { Provider.create!(id: 2, name: 'Looopでんき') }
+  let!(:plan1) { PowerSupplyPlan.create!(id: 3, provider_id: 1, name: 'ずっとも電気1') }
+  let!(:plan2) { PowerSupplyPlan.create!(id: 4, provider_id: 2, name: 'おうちプラン') }
+  let!(:meter_rate_charge1) { MeterRateCharge.create!(power_supply_plan_id: 3, min_meter_rate: 0, max_meter_rate: 140, price: 23.67) }
+  let!(:meter_rate_charge2) { MeterRateCharge.create!(power_supply_plan_id: 3, min_meter_rate: 141, max_meter_rate: 350, price: 23.88) }
+  let!(:meter_rate_charge3) { MeterRateCharge.create!(power_supply_plan_id: 3, min_meter_rate: 351, max_meter_rate: nil, price: 26.41) }
+  let!(:meter_rate_charge4) { MeterRateCharge.create!(power_supply_plan_id: 4, min_meter_rate: 0, max_meter_rate: nil, price: 28.8) }
+
+  describe '#calculate_charge' do
+    context 'calculate on 3 steps plan' do
+      it 'calculate result with 1st step' do
+        expect(meter_rate_charge1.calculate_charge(120).to_f).to eq 2840.4
+        expect(meter_rate_charge1.calculate_charge(140).to_f).to eq 3313.8
+        expect(meter_rate_charge1.calculate_charge(150).to_f).to eq 3313.8
+      end
+
+      it 'calculate result with middle step' do
+        expect(meter_rate_charge2.calculate_charge(150).to_f).to eq 238.8
+        expect(meter_rate_charge2.calculate_charge(350).to_f).to eq 5014.8
+        expect(meter_rate_charge2.calculate_charge(400).to_f).to eq 5014.8
+      end
+
+      it 'calculate result with highest step' do
+        expect(meter_rate_charge3.calculate_charge(351).to_f).to eq 26.41
+        expect(meter_rate_charge3.calculate_charge(400).to_f).to eq 1320.5
+      end
+    end
+
+    context 'calculate on single step plan' do
+      it 'calculate result with single step plan' do
+        expect(meter_rate_charge4.calculate_charge(100).to_f).to eq 2880
+      end
+    end
+  end
+end
diff --git a/serverside_challenge_2/challenge/spec/models/power_supply_plan.rb b/serverside_challenge_2/challenge/spec/models/power_supply_plan.rb
new file mode 100644
index 000000000..331e86c5c
--- /dev/null
+++ b/serverside_challenge_2/challenge/spec/models/power_supply_plan.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe PowerSupplyPlan, type: :model do
+  let!(:provider) { Provider.create!(id: 1, name: '東京ガス') }
+  let!(:plan) { PowerSupplyPlan.create!(id: 3, provider_id: 1, name: 'ずっとも電気1') }
+  let!(:basic_charge1) { BasicCharge.create!(power_supply_plan_id: 3, amp: 30, price: 858.0) }
+  let!(:basic_charge2) { BasicCharge.create!(power_supply_plan_id: 3, amp: 40, price: 1144.0) }
+  let!(:basic_charge3) { BasicCharge.create!(power_supply_plan_id: 3, amp: 50, price: 1430.0) }
+  let!(:basic_charge4) { BasicCharge.create!(power_supply_plan_id: 3, amp: 60, price: 1716.0) }
+  let!(:meter_rate_charge1) do
+    MeterRateCharge.create!(power_supply_plan_id: 3, min_meter_rate: 0, max_meter_rate: 140, price: 23.67)
+  end
+  let!(:meter_rate_charge2) do
+    MeterRateCharge.create!(power_supply_plan_id: 3, min_meter_rate: 141, max_meter_rate: 350, price: 23.88)
+  end
+  let!(:meter_rate_charge3) do
+    MeterRateCharge.create!(power_supply_plan_id: 3, min_meter_rate: 351, max_meter_rate: nil, price: 26.41)
+  end
+  let(:amp) { 10 }
+  let(:meter_rate) { 120 }
+  describe '#calculate_total_amount' do
+    context 'when no meter rate charge available ' do
+      it 'returns nil' do
+        expect(plan.calculate_total_amount(amp, meter_rate)).to be nil
+      end
+    end
+
+    context 'when meter rate charge available' do
+      it 'calculate with designated basic charge' do
+        allow(plan).to receive(:calculate_meter_rate_charge).with(meter_rate).and_return(1000.00)
+        expect(plan.calculate_total_amount(30, meter_rate).to_f).to eq 1858.00
+      end
+    end
+  end
+
+  describe '#calculate_meter_rate_charge' do
+    it 'returns calculation result with 1st step only' do
+      expect(plan.calculate_meter_rate_charge(meter_rate).to_f).to eq 2840.40
+    end
+    it 'returns calculation result with 1st and 2nd step' do
+      expect(plan.calculate_meter_rate_charge(150).to_f).to eq 3552.6
+    end
+  end
+end
diff --git a/serverside_challenge_2/challenge/spec/rails_helper.rb b/serverside_challenge_2/challenge/spec/rails_helper.rb
new file mode 100644
index 000000000..0d761946b
--- /dev/null
+++ b/serverside_challenge_2/challenge/spec/rails_helper.rb
@@ -0,0 +1,69 @@
+# This file is copied to spec/ when you run 'rails generate rspec:install'
+require 'spec_helper'
+ENV['RAILS_ENV'] ||= 'test'
+require_relative '../config/environment'
+# Prevent database truncation if the environment is production
+abort("The Rails environment is running in production mode!") if Rails.env.production?
+# Uncomment the line below in case you have `--require rails_helper` in the `.rspec` file
+# that will avoid rails generators crashing because migrations haven't been run yet
+# return unless Rails.env.test?
+require 'rspec/rails'
+# Add additional requires below this line. Rails is not loaded until this point!
+
+# Requires supporting ruby files with custom matchers and macros, etc, in
+# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
+# run as spec files by default. This means that files in spec/support that end
+# in _spec.rb will both be required and run as specs, causing the specs to be
+# run twice. It is recommended that you do not name files matching this glob to
+# end with _spec.rb. You can configure this pattern with the --pattern
+# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
+#
+# The following line is provided for convenience purposes. It has the downside
+# of increasing the boot-up time by auto-requiring all files in the support
+# directory. Alternatively, in the individual `*_spec.rb` files, manually
+# require only the support files necessary.
+#
+# Rails.root.glob('spec/support/**/*.rb').sort_by(&:to_s).each { |f| require f }
+
+# Checks for pending migrations and applies them before tests are run.
+# If you are not using ActiveRecord, you can remove these lines.
+begin
+  ActiveRecord::Migration.maintain_test_schema!
+rescue ActiveRecord::PendingMigrationError => e
+  abort e.to_s.strip
+end
+RSpec.configure do |config|
+  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
+  config.fixture_path = Rails.root.join('spec/fixtures')
+
+  # If you're not using ActiveRecord, or you'd prefer not to run each of your
+  # examples within a transaction, remove the following line or assign false
+  # instead of true.
+  config.use_transactional_fixtures = true
+
+  # You can uncomment this line to turn off ActiveRecord support entirely.
+  # config.use_active_record = false
+
+  # RSpec Rails uses metadata to mix in different behaviours to your tests,
+  # for example enabling you to call `get` and `post` in request specs. e.g.:
+  #
+  #     RSpec.describe UsersController, type: :request do
+  #       # ...
+  #     end
+  #
+  # The different available types are documented in the features, such as in
+  # https://rspec.info/features/7-1/rspec-rails
+  #
+  # You can also this infer these behaviours automatically by location, e.g.
+  # /spec/models would pull in the same behaviour as `type: :model` but this
+  # behaviour is considered legacy and will be removed in a future version.
+  #
+  # To enable this behaviour uncomment the line below.
+  # config.infer_spec_type_from_file_location!
+
+  # Filter lines from Rails gems in backtraces.
+  config.filter_rails_from_backtrace!
+  # arbitrary gems may also be filtered via:
+  # config.filter_gems_from_backtrace("gem name")
+  # 
+end
diff --git a/serverside_challenge_2/challenge/spec/services/power_supply_plan_simulator.rb b/serverside_challenge_2/challenge/spec/services/power_supply_plan_simulator.rb
new file mode 100644
index 000000000..fee48dd72
--- /dev/null
+++ b/serverside_challenge_2/challenge/spec/services/power_supply_plan_simulator.rb
@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'PowerSupplyPlanSimulator' do
+  context 'when input parameter is valid' do
+    let(:service) { PowerSupplyPlanSimulator.new(amp, meter_rate) }
+    let(:result) { service.call }
+    let(:amp) { 10 }
+    let(:meter_rate) { 120 }
+    let(:provider1) { double(Provider, name: '東京電力エナジーパートナー') }
+    let(:provider2) { double(Provider, name: '東京ガス') }
+    let(:plan1) { double(PowerSupplyPlan, name: '従量電灯B', provider: provider1) }
+    let(:plan2) { double(PowerSupplyPlan, name: 'ずっとも電気1', provider: provider2) }
+
+    it 'returns all valid array' do
+      allow(PowerSupplyPlan).to receive(:includes).and_return([plan1, plan2])
+      allow(plan1).to receive(:calculate_total_amount).with(amp, meter_rate).and_return 4101.6
+      allow(plan2).to receive(:calculate_total_amount).with(amp, meter_rate).and_return 4556.4
+
+      expect(result.length).to eq 2
+      expect(result).to include({ "provider_name": '東京電力エナジーパートナー', plan_name: '従量電灯B', price: 4101.6 })
+      expect(result).to include({ "provider_name": '東京ガス', plan_name: 'ずっとも電気1', price: 4556.4 })
+    end
+
+    it 'returns result with basic_charge availble plans' do
+      allow(PowerSupplyPlan).to receive(:includes).and_return([plan1, plan2])
+      allow(plan1).to receive(:calculate_total_amount).with(amp, meter_rate).and_return 4101.6
+      allow(plan2).to receive(:calculate_total_amount).with(amp, meter_rate).and_return nil
+
+      expect(result.length).to eq 1
+      expect(result).to include({ "provider_name": '東京電力エナジーパートナー', plan_name: '従量電灯B', price: 4101.6 })
+      expect(result).not_to include({ "provider_name": '東京ガス', plan_name: 'ずっとも電気1', price: 4556.4 })
+    end
+  end
+
+  context 'when input parameter is invalid' do
+    let(:service) { PowerSupplyPlanSimulator.new(amp, meter_rate) }
+    let(:result) { service.call }
+
+    context 'invalid amp' do
+      let(:amp) { -10 }
+      let(:meter_rate) { 120 }
+
+      it 'validate_params to be false and return error hash ' do
+        expect(result.is_a?(Hash)).to be_truthy
+      end
+
+      it 'returns amp invalid error' do
+        expect(result.is_a?(Hash)).to be_truthy
+        expect(result[:error][:message]).to start_with "リクエストパラメータ 'amp' の値が不正です。"
+      end
+    end
+
+    context 'invalid meter_rate' do
+      let(:amp) { 10 }
+      let(:meter_rate) { -120 }
+
+      it 'validate_params to be false' do
+        expect(result.is_a?(Hash)).to be_truthy
+      end
+
+      it 'return meter_rate invalid error' do
+        expect(result[:error][:message]).to start_with "リクエストパラメータ 'meter_rate' の値が不正です。"
+      end
+    end
+
+    context 'amp is missing' do
+      let(:amp) { nil }
+      let(:meter_rate) { 120 }
+
+      it 'validate_params to be false' do
+        expect(result.is_a?(Hash)).to be_truthy
+      end
+
+      it 'return amp missing error' do
+        expect(result.is_a?(Hash)).to be_truthy
+        expect(result[:error][:message]).to eq "リクエストパラメータ 'amp' が不足しています。"
+      end
+    end
+
+    context 'meter_rate is missing' do
+      let(:amp) { 10 }
+      let(:meter_rate) { nil }
+
+      it 'validate_params to be false' do
+        expect(result.is_a?(Hash)).to be_truthy
+      end
+
+      it 'return amp missing error' do
+        expect(result.is_a?(Hash)).to be_truthy
+        expect(result[:error][:message]).to eq "リクエストパラメータ 'meter_rate' が不足しています。"
+      end
+    end
+  end
+end
diff --git a/serverside_challenge_2/challenge/spec/spec_helper.rb b/serverside_challenge_2/challenge/spec/spec_helper.rb
new file mode 100644
index 000000000..327b58ea1
--- /dev/null
+++ b/serverside_challenge_2/challenge/spec/spec_helper.rb
@@ -0,0 +1,94 @@
+# This file was generated by the `rails generate rspec:install` command. Conventionally, all
+# specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
+# The generated `.rspec` file contains `--require spec_helper` which will cause
+# this file to always be loaded, without a need to explicitly require it in any
+# files.
+#
+# Given that it is always loaded, you are encouraged to keep this file as
+# light-weight as possible. Requiring heavyweight dependencies from this file
+# will add to the boot time of your test suite on EVERY test run, even for an
+# individual file that may not need all of that loaded. Instead, consider making
+# a separate helper file that requires the additional dependencies and performs
+# the additional setup, and require it from the spec files that actually need
+# it.
+#
+# See https://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+RSpec.configure do |config|
+  # rspec-expectations config goes here. You can use an alternate
+  # assertion/expectation library such as wrong or the stdlib/minitest
+  # assertions if you prefer.
+  config.expect_with :rspec do |expectations|
+    # This option will default to `true` in RSpec 4. It makes the `description`
+    # and `failure_message` of custom matchers include text for helper methods
+    # defined using `chain`, e.g.:
+    #     be_bigger_than(2).and_smaller_than(4).description
+    #     # => "be bigger than 2 and smaller than 4"
+    # ...rather than:
+    #     # => "be bigger than 2"
+    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
+  end
+
+  # rspec-mocks config goes here. You can use an alternate test double
+  # library (such as bogus or mocha) by changing the `mock_with` option here.
+  config.mock_with :rspec do |mocks|
+    # Prevents you from mocking or stubbing a method that does not exist on
+    # a real object. This is generally recommended, and will default to
+    # `true` in RSpec 4.
+    mocks.verify_partial_doubles = true
+  end
+
+  # This option will default to `:apply_to_host_groups` in RSpec 4 (and will
+  # have no way to turn it off -- the option exists only for backwards
+  # compatibility in RSpec 3). It causes shared context metadata to be
+  # inherited by the metadata hash of host groups and examples, rather than
+  # triggering implicit auto-inclusion in groups with matching metadata.
+  config.shared_context_metadata_behavior = :apply_to_host_groups
+
+# The settings below are suggested to provide a good initial experience
+# with RSpec, but feel free to customize to your heart's content.
+=begin
+  # This allows you to limit a spec run to individual examples or groups
+  # you care about by tagging them with `:focus` metadata. When nothing
+  # is tagged with `:focus`, all examples get run. RSpec also provides
+  # aliases for `it`, `describe`, and `context` that include `:focus`
+  # metadata: `fit`, `fdescribe` and `fcontext`, respectively.
+  config.filter_run_when_matching :focus
+
+  # Allows RSpec to persist some state between runs in order to support
+  # the `--only-failures` and `--next-failure` CLI options. We recommend
+  # you configure your source control system to ignore this file.
+  config.example_status_persistence_file_path = "spec/examples.txt"
+
+  # Limits the available syntax to the non-monkey patched syntax that is
+  # recommended. For more details, see:
+  # https://rspec.info/features/3-12/rspec-core/configuration/zero-monkey-patching-mode/
+  config.disable_monkey_patching!
+
+  # Many RSpec users commonly either run the entire suite or an individual
+  # file, and it's useful to allow more verbose output when running an
+  # individual spec file.
+  if config.files_to_run.one?
+    # Use the documentation formatter for detailed output,
+    # unless a formatter has already been configured
+    # (e.g. via a command-line flag).
+    config.default_formatter = "doc"
+  end
+
+  # Print the 10 slowest examples and example groups at the
+  # end of the spec run, to help surface which specs are running
+  # particularly slow.
+  config.profile_examples = 10
+
+  # Run specs in random order to surface order dependencies. If you find an
+  # order dependency and want to debug it, you can fix the order by providing
+  # the seed, which is printed after each run.
+  #     --seed 1234
+  config.order = :random
+
+  # Seed global randomization in this process using the `--seed` CLI option.
+  # Setting this allows you to use `--seed` to deterministically reproduce
+  # test failures related to randomization by passing the same `--seed` value
+  # as the one that triggered the failure.
+  Kernel.srand config.seed
+=end
+end