Back-end developer: ∟📂 Server-side programming (Python,Java,PHP, NodeJs,Go,Rust) ∟📂 Databases (SQL, NoSQL) ∟📂 APIs and web services ∟📂 Security and authentication ∟📂 Caching and performance tuning ∟📂 Scalability and load balancing ∟📂 Deployment and DevOps ∟📂 Data structures and algorithms ∟📂 Error handling and logging ∟📂 Testing ∟📂 Continuous integration and delivery ∟📂 Cloud services and management