diff --git a/Dockerfile.dev b/Dockerfile.dev
index a8ea7f21..3baf5377 100644
--- a/Dockerfile.dev
+++ b/Dockerfile.dev
@@ -16,7 +16,6 @@ RUN apk update && \
     mysql-dev \
     openssh \
     ruby-dev \
-    ruby-json \
     tzdata \
     yaml \
     yaml-dev \
diff --git a/Dockerfile.system-test b/Dockerfile.system-test
index 0bff879c..e6aca55f 100644
--- a/Dockerfile.system-test
+++ b/Dockerfile.system-test
@@ -16,7 +16,6 @@ RUN apk update && \
   mysql-dev \
   openssh \
   ruby-dev \
-  ruby-json \
   tzdata \
   yaml \
   yaml-dev \
diff --git a/README.md b/README.md
index 3132d0a0..c0b7e56f 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 [![Gem Version](https://badge.fury.io/rb/bucky-core.svg)](https://badge.fury.io/rb/bucky-core) [![CircleCI](https://circleci.com/gh/lifull-dev/bucky-core/tree/master.svg?style=svg)](https://circleci.com/gh/lifull-dev/bucky-core/tree/master) [![Maintainability](https://api.codeclimate.com/v1/badges/adf9599d98a55ac87a2e/maintainability)](https://codeclimate.com/github/lifull-dev/bucky-core/maintainability) [![Test Coverage](https://api.codeclimate.com/v1/badges/adf9599d98a55ac87a2e/test_coverage)](https://codeclimate.com/github/lifull-dev/bucky-core/test_coverage)
 
 ## Overview
-Bucky-core can run test code which is written in YAML. End-to-End test (working with Selenium) and Linkstatus test (HTTP status check) are supported in default. Page object model pattern and page based element management is the main concept in Bucky-core.  You can create scenarios and execute it easily by using Bucky-core.
+Bucky-core can run test code which is written in YAML form. End-to-End test (working with Selenium) and Linkstatus test (HTTP status check) are supported in default. Page object model pattern and page based element management is the main concept in Bucky-core.  You can create scenarios and execute it easily by using Bucky-core.
 
 When working with [Bucky-management](https://github.com/lifull-dev/bucky-management), Bucky-core can also record test results. You can make test results visualization by using Bucky-management.