diff --git a/.gitmodules b/.gitmodules
index b9efa1a1..0f95dc17 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -202,6 +202,9 @@
 [submodule "gems/recaptcha/5.15/_src"]
 	path = gems/recaptcha/5.15/_src
 	url = https://github.com/ambethia/recaptcha.git
+[submodule "gems/dotenv-rails/2.8/_src"]
+	path = gems/dotenv-rails/2.8/_src
+	url = https://github.com/bkeepers/dotenv.git
 [submodule "gems/activerecord-import/1.5/_src"]
 	path = gems/activerecord-import/1.5/_src
 	url = https://github.com/zdennis/activerecord-import.git
diff --git a/gems/dotenv-rails/2.8/_scripts/test b/gems/dotenv-rails/2.8/_scripts/test
new file mode 100755
index 00000000..106695f3
--- /dev/null
+++ b/gems/dotenv-rails/2.8/_scripts/test
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+# Exit command with non-zero status code, Output logs of every command executed, Treat unset variables as an error when substituting.
+set -eou pipefail
+# Internal Field Separator - Linux shell variable
+IFS=$'\n\t'
+# Print shell input lines
+set -v
+
+# Set RBS_DIR variable to change directory to execute type checks using `steep check`
+RBS_DIR=$(cd $(dirname $0)/..; pwd)
+# Set REPO_DIR variable to validate RBS files added to the corresponding folder
+REPO_DIR=$(cd $(dirname $0)/../../..; pwd)
+# Validate RBS files, using the bundler environment present
+bundle exec rbs --repo $REPO_DIR -r dotenv-rails:2.8 validate --silent
+
+cd ${RBS_DIR}/_test
+# Run type checks
+bundle exec steep check
+
+$(git rev-parse --show-toplevel)/bin/check-untyped-call.rb
diff --git a/gems/dotenv-rails/2.8/_src b/gems/dotenv-rails/2.8/_src
new file mode 160000
index 00000000..45b712a5
--- /dev/null
+++ b/gems/dotenv-rails/2.8/_src
@@ -0,0 +1 @@
+Subproject commit 45b712a5c17d707959df69595b1dd12e0a18cfd1
diff --git a/gems/dotenv-rails/2.8/_test/Steepfile b/gems/dotenv-rails/2.8/_test/Steepfile
new file mode 100644
index 00000000..a7e92930
--- /dev/null
+++ b/gems/dotenv-rails/2.8/_test/Steepfile
@@ -0,0 +1,11 @@
+D = Steep::Diagnostic
+
+target :test do
+  check "."
+  signature "."
+
+  repo_path "../../../"
+  library "dotenv-rails"
+
+  configure_code_diagnostics(D::Ruby.all_error)
+end
diff --git a/gems/dotenv-rails/2.8/_test/env_files/file1.env b/gems/dotenv-rails/2.8/_test/env_files/file1.env
new file mode 100644
index 00000000..3f094562
--- /dev/null
+++ b/gems/dotenv-rails/2.8/_test/env_files/file1.env
@@ -0,0 +1 @@
+KEY1=key1
diff --git a/gems/dotenv-rails/2.8/_test/env_files/file2.env b/gems/dotenv-rails/2.8/_test/env_files/file2.env
new file mode 100644
index 00000000..99d6ce17
--- /dev/null
+++ b/gems/dotenv-rails/2.8/_test/env_files/file2.env
@@ -0,0 +1,2 @@
+KEY1=key1-hoge
+KEY2=key2
diff --git a/gems/dotenv-rails/2.8/_test/test.rb b/gems/dotenv-rails/2.8/_test/test.rb
new file mode 100644
index 00000000..899e9f4e
--- /dev/null
+++ b/gems/dotenv-rails/2.8/_test/test.rb
@@ -0,0 +1,18 @@
+# Write Ruby code to test the RBS.
+# It is type checked by `steep check` command.
+
+require 'dotenv'
+
+Dotenv.load
+Dotenv.load('./env_files/file1.env', './env_files/file2.env')
+Dotenv.load('./env_files/file3.env')
+
+Dotenv.load!
+Dotenv.load!('./env_files/file1.env', './env_files/file2.env')
+
+Dotenv.require_keys('KEY1', 'KEY2')
+
+pp Dotenv.parse('./env_files/file1.env', './env_files/file2.env')['KEY1']
+
+Dotenv.overload('./env_files/file1.env', './env_files/file2.env')
+Dotenv.overload!('./env_files/file1.env', './env_files/file2.env')
diff --git a/gems/dotenv-rails/2.8/dotenv-rails.rbs b/gems/dotenv-rails/2.8/dotenv-rails.rbs
new file mode 100644
index 00000000..f8063557
--- /dev/null
+++ b/gems/dotenv-rails/2.8/dotenv-rails.rbs
@@ -0,0 +1,21 @@
+module Dotenv
+  def self.load: (*String filenames) -> void
+               | () -> void
+  def self.load!: (*String filenames) -> void
+                | () -> void
+
+  def self.require_keys: (*String keys) -> void
+  def self.parse: (*String filenames) -> Environment
+
+  def self.overload: (*String filenames) -> void
+                   | () -> void
+  def self.overload!: (*String filenames) -> void
+                    | () -> void
+
+  class Environment < Hash[String, untyped]
+    attr_reader filename: String
+
+    def initialize: (String filename, boolish is_load) -> void
+    def load: (boolish is_load) -> self
+  end
+end