Software suitability for meeting user needs is a non-functional quality attribute, and here's why

Think about the software you rely on day in and day out. It’s not just the features it offers, but how it behaves while you’re using those features. That “how” is what people call non-functional requirements. They’re the seasoning on the main dish—taste, texture, and ease—more than the core ingredients themselves.

Let me explain the big idea with a simple setup. Imagine you’re choosing a project-tracking tool. Functional requirements would spell out things like “create a project,” “assign tasks,” or “generate status reports.” Those are the concrete actions the system must perform. Non-functional requirements, on the other hand, describe how well the system performs those actions. Can you find what you need quickly? Is the system reliable? Are the pages loading fast enough on a phone during a commute? Can you trust sensitive data to stay private? These questions aren’t about what the tool does, but how well it does it.

Here’s the question you’ll often see in assessment materials, sketched in a crisp multiple-choice format:

Suitability of the software to fulfill the needs of the user is an example of a quality attribute of what type of requirement?

A. Functional

B. Non-functional

C. Performance

D. Quality of Service

If you’re thinking purely in terms of definitions, you might blink and choose A, Functional. After all, “suitability to fulfill needs” sounds like a job for what the software can do. But here’s the crux: suitability isn’t about the functions themselves. It’s about how those functions are delivered—the user experience, the constraints, and the trade-offs that shape whether the software actually meets real-world needs. That’s the realm of non-functional requirements.

Why non-functional fits better than functional

First, separate the two ideas clearly. Functional requirements describe what the system must do. They define the verbs: login, search, filter, export. Non-functional requirements describe how the system should be while it’s doing those things. They cover the quality of the experience: usability, reliability, performance, security, accessibility, and maintainability. In short, functional asks, “What can you do?” non-functional asks, “How well does it work while you do it?”

Now, when we talk about “suitability to fulfill needs,” we’re judging quality. Does the software fit the user’s context, work well under expected load, recover gracefully after a glitch, present information in an understandable way, and keep data secure? Those criteria are not about adding more features; they’re about ensuring those features can be trusted, learned quickly, and used comfortably. That’s exactly what non-functional requirements capture.

A quick mental model helps here. Think of the functions as a car’s features—airbags, Bluetooth, heated seats. The non-functional attributes are more like how the car feels to drive: acceleration smoothness, braking responsiveness, fuel efficiency, cabin quietness, and tire traction in rain. You can have every feature in the world, but if the ride is loud, unsafe, and unreliable, the car won’t satisfy what you need. The same logic applies to software: features matter, but the experience that accompanies them determines overall suitability.

Common non-functional attributes you’ll encounter

To ground this in real-life terms, here are some non-functional attributes you’ll see mentioned often, with quick examples of what they cover:

• Usability: Is the interface intuitive? Can a new user accomplish core tasks without a long learning curve?

• Reliability: Does the system behave predictably, and does it recover gracefully after failures?

• Performance: Are response times acceptable under typical and peak loads? How fast can a user complete a task?

• Security and privacy: Are data protections robust? Is sensitive information safeguarded from unauthorized access?

• Availability: Is the system up and reachable when users need it? What’s the uptime?

• Accessibility: Can people with different abilities use the software effectively?

• Maintainability: How easy is it to fix issues or make changes without breaking other parts?

• Compatibility: Does the software work well across devices, browsers, and operating systems?

• Scalability: How well does the system handle growth—more users, more data, more transactions?

All of these speak to quality of service, not to a specific feature. They determine whether users actually value the software in real life, not just in a feature checklist.

Why this distinction matters in practice

If you want people to adopt software, you can’t rely on features alone. You need confidence that the product behaves as expected in the real world. A tool might offer a gorgeous dashboard and a powerful export function, but if it crashes during peak hours or leaves sensitive data exposed, users won’t stay. The trade-offs you make between speed, security, and ease of use shape every day decision-making.

This is why non-functional requirements are treated with serious weight in requirements engineering. They drive conversations with stakeholders about risk, cost, and user satisfaction. They influence design decisions, testing plans, and even the way you measure success after a release. In other words, non-functional attributes aren’t “nice-to-haves.” They’re essential to delivering software that people can rely on.

A practical approach to capturing these attributes

If you’re in a role that shapes software requirements, here are a few practical steps to make non-functional attributes observable and testable, not vague and abstract:

• Define concrete metrics: Instead of saying “the app is fast,” specify numbers. For example, “page load time under 2 seconds for 95% of user requests,” or “99.9% uptime per month.”

• Tie metrics to user tasks: Link performance targets to real actions, like “search results appear within 1 second for typical queries.”

• Prioritize by context: The importance of certain attributes will shift with the context. A mobile banking app might emphasize security and accessibility, while an analytics dashboard might stress performance and scalability.

• Include acceptance criteria: For each non-functional attribute, add acceptance criteria that teams can test against. This makes expectations clear and testable.

• Balance trade-offs: Rarely can you optimize everything at once. Document the rationale behind prioritizing some attributes over others and how you’ll monitor the impact.

A few tangible examples to illustrate

• Usability example: A CRM tool is functionally capable of managing contacts and opportunities, but if sales reps struggle to find the “create new contact” button, adoption will lag. An acceptance criterion could be: “New contact creation must be achievable within two clicks from the main dashboard for 90% of users.”

• Reliability example: A health-records system must handle transient outages without data loss. Acceptance criteria might include: “Data integrity checks pass after every reconnection, with automatic retry logic if a write fails.”

• Security example: An e-commerce platform stores payment data. Acceptance criteria could state: “All sensitive data is encrypted in transit and at rest; PCI compliance is maintained.”

• Accessibility example: A public portal should be usable by keyboard-only navigation and screen readers, with WCAG 2.1 AA conformance verified through testing.

Bringing it back to the bigger picture

So, where does this fit into the broader discipline of requirements engineering? Non-functional attributes anchor the user experience in reality. They remind teams that “meeting the user’s needs” isn’t only about what the product can do, but about how well it does it in the user’s environment. When you map requirements to real-world contexts, you avoid the pitfall of delivering a feature-rich product that nobody enjoys using.

If you’ve spent time studying foundational concepts, you’ll recognize a familiar model here. Quality models—like ISO 25010—group attributes into families and help teams speak the same language about quality. It’s less about prescribing a single path and more about ensuring the key questions get asked: What matters to users? How will we measure it? What risks do we tolerate? And how will we test to prove it?

A few reflections to keep in mind

• People first: Technology is a means to an end. Non-functional attributes are the bridge from capability to value. A tool that feels clunky may fail even if it’s technically correct.

• Trade-offs are inevitable: You might have to trade a bit of speed for stronger security or vice versa. Document the decision and monitor outcomes.

• Context matters: A tool deployed in a hospital environment has different non-functional priorities than a startup internal tool. Tailor your requirements to the setting.

• You can test what you value: Define concrete acceptance criteria, collect metrics, and run experiments or load tests to verify performance and reliability under realistic conditions.

A closing thought

The notion of “suitability to fulfill needs” sits squarely in the non-functional camp, even though it sounds like a feature cue. It’s about the experience—the confidence users feel, the simplicity they enjoy, the trust they place in the system when it matters most. If you want software that people actually reach for and rely on, you don’t just build the right functions. You shape a product that behaves consistently, safely, and pleasantly in the real world.

If you’re exploring these ideas with an eye toward software projects, you’ll notice a consistent thread: the quality attributes you decide to prioritize shape every downstream choice—from architecture and design to testing and release. And yes, the term “non-functional” may seem a bit clinical, but it’s a powerful lens. It helps you translate human needs into measurable criteria and, ultimately, into products that feel right when you use them.

So next time you evaluate a tool or draft a requirements spec, pause for a moment on suitability. Ask not only what the software can do, but how well it does it for the people who depend on it. The answer to that question often tells you everything you need to know about the true value of the system.

If you’re curious about the broader landscape of quality attributes, there are practical resources and real-world case studies that show how teams balance usability, reliability, and security in different industries. It’s a living conversation, not a checkbox. And that conversation, more than anything, determines whether software becomes a trusted companion in daily work—or just another tool that sits on the shelf.