Every time a website crashes under load, or a feature responds so slowly that users abandon it, you’ve run into a missing or poorly defined non-functional requirement. Studies show that unclear requirements contribute to nearly 47% of project failures. Most of those failures come from missing or weak non-functional requirements.
If you’re a business owner trying to steer technology or a DevOps engineer building for uptime and performance, understanding sample non functional requirements is critical. This article walks you step-by-step through how to think about them, write them well, and keep them alive throughout your project lifecycle.
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Here’s what we’ll cover:
- What non-functional requirements are and why they matter
- Core categories of non-functional requirements (with sample items)
- How to write good non-functional requirements: templates & steps
- Testing, validating, and measuring them
- How DevOps & continuous delivery impact non-functional requirements
- Real examples & a mini case study you can learn from
- Common pitfalls, gaps, and how to avoid them
- FAQ — “People Also Ask” style
Sample Non Functional Requirements: Your Guide to Quality Attributes
In short: while functional requirements specify what a system does (e.g. “the system shall allow user login”), non-functional requirements describe how it must perform (e.g. “login must succeed within 2 seconds under up to 5,000 concurrent logins”).
Why Non-Functional Requirements Matter
When I’ve tested projects in the real world, the features often worked—but they failed under load, or user experience degraded. Why? Because non-functional aspects were forgotten or vague. Crafting good NFRs protects you from that failure mode.
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- They define quality expectations—performance, security, availability, usability, etc.
- They guide architecture and infrastructure choices.
- They enable measurable validation (“Did we meet the bar?”).
- They reduce rework by surfacing expectations early.
- They make SLAs and compliance measurable and enforceable.
Key Types & Sample Non Functional Requirements (with Templates)
Each category of non-functional requirement defines a key dimension of quality. Here’s a table showing the major ones and example statements.
| Category | Sample Requirement | Notes |
|---|---|---|
| Performance / Latency | The system must respond to API requests within 200 ms at 1,000 requests per second. | May conflict with heavy validation logic. |
| Scalability / Throughput | The system must scale to support 10× current user base with no more than 10% performance degradation. | Requires architectural foresight and horizontal scaling. |
| Availability / Reliability | The system must maintain 99.95% uptime with a mean time to recovery (MTTR) under 5 minutes. | May increase infrastructure cost. |
| Security / Compliance | All user data must be encrypted using AES-256 at rest and TLS 1.3 in transit. | Encryption adds computational overhead. |
| Maintainability / Operability | Developers must be able to deploy a patch in under 2 hours with zero downtime. | Needs robust CI/CD and rollback pipelines. |
| Usability / Accessibility | The onboarding flow must be completable by a first-time user within 2 minutes and meet WCAG 2.2 AA compliance. | Validated through real user testing. |
| Recoverability / Disaster Recovery | The system must restore operations within 30 minutes after failure; recovery point objective ≤ 5 minutes. | Requires backup, replication, and failover strategies. |
Pro Tip: Never define a requirement that can’t be verified. “Fast” or “secure” means nothing without metrics like “under 200 ms” or “encrypted with AES-256.”
How to Write Good Sample Non Functional Requirements (6 Steps)
- Gather stakeholder expectations. Interview business, operations, and security leads about priorities and acceptable limits.
- Define measurable success metrics. Example: p95 latency, uptime percentage, MTTR, error rate.
- Use SMART criteria. Each requirement should be specific, measurable, achievable, relevant, and time-bound.
- List assumptions and constraints. For example, “Under 20% CPU utilization.”
- Model dependencies and trade-offs. Note which NFRs may conflict (e.g., security vs. performance).
- Review and iterate. Validate requirements with your full DevOps and business team.
Here’s a reusable template:
“Under load of X users, the system shall achieve metric Y (≤ or ≥ value Z) with error rate ≤ N%. Acceptable degradation: up to P% under condition C.”
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Testing & Validation: Ensuring You Meet Your NFRs
Writing NFRs is step one—testing them is where real quality assurance begins. Non-functional testing validates how the system performs under stress, not just whether it works.
- Load Testing: Measure performance under expected and peak loads.
- Stress Testing: Push the system beyond limits to find breakpoints.
- Security Testing: Scan for vulnerabilities, compliance, and encryption strength.
- Usability Testing: Check real-world completion rates and accessibility standards.
- Chaos Testing: Simulate failures to measure recoverability and resilience.
| Stage | Validation Method | Purpose |
|---|---|---|
| QA / Staging | Load and stress testing | Catch bottlenecks early |
| CI/CD Pipeline | Automated performance checks | Block regressions before deploy |
| Production | Monitoring and alerting | Track compliance with NFR targets |
Pro Tip: Tie your NFRs to SLIs (Service Level Indicators) and SLOs (Service Level Objectives). For example, “99.95% of requests must complete in under 300 ms.” LoadFocus helps automate that validation.
DevOps and Continuous Delivery: Keeping NFRs Alive
In DevOps workflows, non-functional requirements can’t be “write once, forget forever.” They must evolve with your system. Embed them in every sprint review, design doc, and monitoring dashboard.
- Include NFR checks in your CI/CD pipelines.
- Automate performance regression tests using tools like LoadFocus.
- Monitor NFR metrics (uptime, latency, error rate) with alerting thresholds.
- Re-baseline every 3–6 months as traffic and architecture evolve.
Pro Tip: Treat NFRs as “contracts” between product, business, and engineering. Each one defines a measurable promise about the system’s behavior.
Case Study: Using LoadFocus to Validate NFRs
When I tested an onboarding API expected to handle 2,000 signups per minute, I defined five non-functional requirements up front. Using LoadFocus, I simulated 2,000 requests per second to verify compliance.
- Throughput: 95th percentile latency ≤ 250 ms, error rate ≤ 1%.
- Availability: 99.9% uptime during load test.
- Scalability: No node exceeded 80% CPU.
- Recovery: Auto failover restored service within 2 minutes.
- Security: All requests served via HTTPS with MFA-enabled access.
Screenshot placeholder: Screenshot of LoadFocus dashboard showing test results with API latency curve under 2,000 RPS and error rate highlighted below 1%.
The test revealed spikes to 300 ms during write bursts. We tuned connection pooling and caching until latency stabilized under 250 ms. The NFRs weren’t just checkboxes—they became active engineering goals.
Common Pitfalls and Gaps to Avoid
- Writing vague, non-measurable requirements (“system must be fast”).
- Skipping trade-off discussions (e.g. security vs. performance).
- Failing to re-evaluate NFRs as systems evolve.
- Leaving NFR ownership unclear between teams.
- Testing only once—instead of monitoring continuously.
Frequently Asked Questions
What is a sample non functional requirement?
A sample non functional requirement is a measurable statement about system behavior, such as “The system shall respond to user queries within 300 ms for 95% of requests.”
Who defines non functional requirements?
They’re typically defined collaboratively by product owners, DevOps engineers, QA testers, and architects. Each group brings a different perspective to performance, reliability, and usability expectations.
Can non functional requirements change over time?
Yes—and they should. As your user base grows or your tech stack evolves, you’ll need to adjust thresholds and metrics to reflect new realities.
How do you test non functional requirements?
Use performance and load testing tools like LoadFocus to simulate real usage, monitor key metrics, and validate whether your application meets defined NFR thresholds.
Conclusion & Key Takeaways
- Non-functional requirements define how well a system performs, not what it does.
- Each NFR must be specific, measurable, and testable.
- Regular testing and monitoring keep them relevant in continuous delivery.
- Tools like LoadFocus make NFR validation effortless by providing automated load and performance testing.
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