How to Measure and Reduce API Latency in C# .NET Applications

API latency — the total time between a client request and server response — significantly affects user experience, scalability, and infrastructure costs in .NET applications. The three main sources of latency are network transmission, server-side processing, and database interactions, each requiring distinct mitigation strategies. Developers can measure latency using tools such as Stopwatch, custom middleware, Application Insights, and distributed tracing platforms like OpenTelemetry or Jaeger. Key optimization techniques include switching from synchronous to asynchronous code with async/await, adding database indexes, using in-memory or Redis caching, and enabling response compression. Additional gains can be achieved by offloading heavy tasks to message queues, reducing payload sizes, and using the faster System.Text.Json serializer.