responsetime

Response time is the elapsed time between issuing a request and receiving a response. In computing and networking, it is often described using metrics such as Time to First Byte (TTFB) and end-to-end response time, which includes network transit, server processing, and client rendering.

Measurements use statistical summaries to capture performance characteristics. Common metrics include the mean and median, along with tail indicators like the p95 or p99 percentile to describe slower responses. Synthetic monitoring probes endpoints at regular intervals, while real-user monitoring (RUM) collects data from actual users. In web contexts, end-user response time relates to how quickly a page becomes usable.

Several factors influence response time. These include network latency, server load, application complexity, database queries, I/O performance, caching effectiveness, and payload size. Bottlenecks can occur at the client, the application server, the database, or external services. Techniques such as caching, content delivery networks (CDNs), and optimized queries commonly reduce response time, particularly for repeated or large requests.

In performance engineering, response time is a central quality attribute tracked through service-level objectives (SLOs) and, where applicable, service-level agreements (SLAs). Optimization approaches include caching, load balancing, query optimization, asynchronous processing, data compression, and hardware scaling. Observability and tracing help locate slow components and reduce tail latency to improve overall user experience.

The term also appears in human factors, where human response time measures the interval between a stimulus and a person’s reaction. This variant informs UI design, safety-critical systems, and studies of cognitive processing.