env_check

https://github.com/0xNadeem/env_check

EnvCheck is a lightweight Ruby gem that ensures your required and optional environment variables are present and valid before your app boots. Features smart config discovery (.env_check.yml or config/env_check.yml), comprehensive type validation with 9 built-in validators, .env loading with dotenv, and professional CLI tools. Framework-agnostic design works with Rails 7.1+ through Rails 8.0+, Ruby 3.0+.