Modern applications depend heavily on APIs. From mobile apps and SaaS platforms to AI-powered services and IoT devices, APIs are the backbone that allows systems to communicate efficiently. In 2026, RESTful APIs remain one of the most widely adopted architectural styles because they are scalable, flexible, and easy to integrate across platforms. However, designing a RESTful API today requires more than simply exposing endpoints and returning JSON responses. Developers now expect better security, predictable structures, faster performance, AI-friendly integrations, and developer-first experiences. Poorly designed APIs create technical debt, security risks, and frustrating integration experiences that slow down product growth. This article explores the best practices for RESTful API design in 2026, covering everything from endpoint naming conventions and versioning strategies to authentication, observability, and AI-era considerations. What Is a RESTful API?…