Performance requirement describes how fast, how many, or how well a system must perform. I use the term “performance requirement” to mean timing, speed, volume, capacity, throughput, latency, and similar measurable characteristics. For example, I specify response time, transactions per second, or maximum concurrent users. In addition, I state the units and measurement method. This makes the requirement testable and clear.
First, I place performance requirements in the requirements classification. Usually, I treat them as a sub-category of quality requirements. However, I also recognize that teams sometimes treat them as a requirement type of their own. Therefore, I link performance requirements to non-functional requirements. Furthermore, I relate them to system requirements and user requirements when appropriate. In other words, I make explicit where the performance need comes from.
Second, I make performance requirements measurable. I write numeric targets. For example, I require “95% of search responses under 300 ms under 1,000 concurrent users.” Thus, I include thresholds, percentiles, and time windows. Moreover, I define load profiles and peak conditions. Consequently, testers can verify whether the system meets the requirement.
Third, I describe the context for measurement. I specify the environment, the test data, and the tools to measure performance. Likewise, I note any constraints such as hardware, network limits, or third-party services. Also, I indicate acceptable degradation modes. For instance, I allow reduced throughput during scheduled maintenance. Meanwhile, I avoid vague phrases like “fast” or “scalable.” Instead, I use concrete metrics.
Fourth, I connect performance requirements to architecture and design. Performance requirements often influence the system architecture. For example, latency targets may drive caching or microservice design. Therefore, I share performance requirements early with architects and developers. In addition, I include them in the requirements management plan. As a result, teams plan capacity, reliability, and scalability appropriately.
Fifth, I ensure traceability and change control. I link each performance requirement to its source. Thus, I record stakeholder needs, business rules, or contractual SLAs that justify the target. Then, I version the requirement and manage changes. Consequently, I avoid unplanned impacts on system behavior.
Sixth, I describe acceptance criteria. I define how to prove compliance. For example, I list test scenarios, monitoring KPIs, and observation windows. Also, I state who accepts the result. Furthermore, I include fall-back thresholds and remediation steps. This reduces ambiguity during validation and operations.
Seventh, I consider solution dependence. Sometimes I phrase performance goals independently of the solution. For example, I state a business goal like “customers will experience no more than 2-second wait time.” However, sometimes I give solution-related guidance. For instance, I require that a specific service handle 10,000 requests per minute. Thus, I balance goal-level and solution-level descriptions.
Finally, I apply best practices when writing performance requirements. To do so, I keep sentences short. In addition, I use clear metrics and test methods. Early on, I involve stakeholders. As the context changes, I update requirements. Consequently, teams implement systems that meet business needs and contractual obligations.
If you want, I can give templates for performance requirement statements. Then, you can adapt them to your project and measurement tools.