The article provides a comprehensive guide on building a RESTful API using Ruby on Rails, focusing on an interface for the Cowsay program, which allows users to send text that can be customized with various parameters. It begins with setup instructions, including installing Ruby and Rails, and creating a lean Rails application tailored for API development by excluding unnecessary modules like ActiveRecord. The tutorial includes steps for adding a controller and defining a single endpoint, /say, which processes POST requests to generate responses. It further explains how to test the API using tools like curl and Postman, implement additional parameters for customization, and introduce validation for input parameters. The guide also covers deploying the API to Heroku for hosting and publishing it on RapidAPI to make it accessible to other developers. Finally, it suggests exploring database setup on Heroku and reviewing RapidAPI's documentation for further enhancement of API functionalities.