As an online business grows in popularity it can highlight scalability problems in your architecture. Certain hardware and/or software components can struggle to keep up with increased demand and it may not be easy or cost-effective to address this by extending them in their present form, especially when the demand is ‘spiky’ in nature. My team was recently faced with such an issue. We decided to engineer our way out of the problem by designing a more scalable replacement solution. Key technical requirements for the new solution included the throughput and latency of a public web API. In this post I share details of how you can measure these performance characteristics of an API using Apache JMeter, and in the process I identify a very useful supporting JMeter plugin.