Backend developers are responsible for application logic, APIs, databases, authentication, security, and communication between different systems.
Important backend skills include a programming language such as Java, Python, C#, JavaScript or Go; SQL; REST APIs; Git; databases; authentication; testing; debugging; and basic deployment knowledge.
Java developers should additionally understand Spring Boot, Spring Data JPA, Hibernate, Spring Security, Maven or Gradle, and unit testing.
As experience grows, developers can move toward Docker, caching, message queues, microservices, cloud platforms, system design, and performance optimization.