diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
index de49c1e..44513f9 100644
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -3,7 +3,7 @@
     "dockerfile": "Dockerfile",
     "args": {
       "VARIANT": "3.3",
-      "NODE_VERSION": "21"
+      "NODE_VERSION": "20"
     }
   },
   "postCreateCommand": [".devcontainer/bootstrap.sh"]
diff --git a/.github/workflows/prettier.yml b/.github/workflows/prettier.yml
new file mode 100644
index 0000000..3f41942
--- /dev/null
+++ b/.github/workflows/prettier.yml
@@ -0,0 +1,16 @@
+name: Format Files
+
+on:
+  - push
+
+jobs:
+  prettier:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 20.x
+          cache: yarn
+      - run: yarn install --frozen-lockfile
+      - run: yarn run prettier --check '**/**.{yml,md}'
diff --git a/.gitignore b/.gitignore
index f40fbd8..5820dc2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,5 @@ _site
 .jekyll-cache
 .jekyll-metadata
 vendor
+
+node_modules
diff --git a/README.md b/README.md
index 8122d08..6ddee67 100644
--- a/README.md
+++ b/README.md
@@ -1 +1 @@
-# anipos.github.io
\ No newline at end of file
+# anipos.github.io
diff --git a/_config.yml b/_config.yml
index f9c3447..961e258 100644
--- a/_config.yml
+++ b/_config.yml
@@ -26,7 +26,7 @@ description: >- # this means to ignore newlines until "baseurl:"
 baseurl: "" # the subpath of your site, e.g. /blog
 url: "https://anipos.github.io" # the base hostname & protocol for your site, e.g. http://example.com
 twitter_username: anipos_co_jp
-github_username:  anipos
+github_username: anipos
 
 # Build settings
 theme: minima
@@ -35,7 +35,6 @@ plugins:
   - jekyll-mentions
   - jekyll-seo-tags
   - jekyll-sitemap
-
 # Exclude from processing.
 # The following items will not be processed, by default.
 # Any item listed under the `exclude:` key here will be automatically added to
diff --git a/_posts/2024-02-02-rails-7-1-introduced-filtering-tests-by-line-ranges.md b/_posts/2024-02-02-rails-7-1-introduced-filtering-tests-by-line-ranges.md
index 2612a01..350aeda 100644
--- a/_posts/2024-02-02-rails-7-1-introduced-filtering-tests-by-line-ranges.md
+++ b/_posts/2024-02-02-rails-7-1-introduced-filtering-tests-by-line-ranges.md
@@ -1,6 +1,6 @@
 ---
 layout: post
-title:  "Rails 7.1で指定した範囲の行にあるテストを実行可能になりました"
+title: "Rails 7.1で指定した範囲の行にあるテストを実行可能になりました"
 author: "@shouichi"
 date: 2024-02-02 17:26:14 +09:00
 categories: rails
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..85ce21b
--- /dev/null
+++ b/package.json
@@ -0,0 +1,6 @@
+{
+  "private": true,
+  "devDependencies": {
+    "prettier": "*"
+  }
+}
diff --git a/yarn.lock b/yarn.lock
new file mode 100644
index 0000000..5f95aef
--- /dev/null
+++ b/yarn.lock
@@ -0,0 +1,8 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+prettier@*:
+  version "3.2.5"
+  resolved "https://registry.yarnpkg.com/prettier/-/prettier-3.2.5.tgz#e52bc3090586e824964a8813b09aba6233b28368"
+  integrity sha512-3/GWa9aOC0YeD7LUfvOG2NiDyhOWRvt1k+rcKhOuYnMY24iiCphgneUfJDyFXd6rZCAnuLBv6UeAULtrhT/F4A==