The guide provides a comprehensive overview of building RESTful APIs using Node.js, focusing on the comparison of various libraries and design decisions. It emphasizes the importance of understanding REST design principles such as semantic URI endpoints, statelessness, and idempotence, and discusses the main layers of a tech stack, including HTTP servers, routing, JSON serialization, databases, and security. It highlights popular frameworks like Express, Koa, Hapi, and Restify, and delves into the use of JSON Web Tokens (JWT) and opaque tokens for authentication. Additionally, it discusses rate limiting, reverse proxies, and the potential of generating APIs automatically through frameworks like Loopback, Nodal, and Deployd. The guide also touches on the use of WebSockets for real-time applications, although noting their scalability challenges compared to HTTP REST APIs. Overall, it depicts the Node.js ecosystem as highly flexible and growing, with Express and React being popular choices for API development.