In many software projects, Functional Requirements get most of the attention – what the system should do, how data should be processed… But did you know that Non-Functional Requirements (NFRs) are often the true factors that determine system performance, security, user experience, and scalability?

Based on real-world experience, BABOK v3, Requirement Quest, and enterprise templates, we’ve compiled 23 crucial NFRs that Business Analysts and Solution Architects frequently encounter, from security, performance, usability, to legal compliance and scalability.

This article will help you:

• Identify NFRs that are often overlooked.
• Understand the importance of each requirement type.
• Apply them in projects to avoid system failures, performance bottlenecks, and user complaints.

Are you ready to explore the 23 “invisible” NFRs that can make or break your project?

While BABOK v3.0 officially classifies NFRs into 15 types, real-world projects are often more complex. Based on my experience, references from BABOK, Requirement Quest, and several enterprise templates, I’ve expanded the list to 23 practical types of Non-Functional Requirements that business analysts and system designers frequently encounter.

Let’s go through them — concise and easy to digest, but packed with practical value.

1. Security

Security defines the rules that protect user data and system integrity — from login to logout, from data input to printing reports.

Typical examples include:

• Passwords must be hashed (e.g., MD5 or stronger algorithms).
• The system deactivates after 5 failed login attempts.
• Sensitive user data (password, phone, ID, email) must be encrypted using 1024-bit SSL.
• Reset password links are sent only to the registered email address.
• Payment modules must not store credit or debit card data.

2. Performance

Performance ensures that the system runs smoothly and efficiently.
Common metrics include:

• Response time per transaction
• Transactions per second
• System capacity (number of concurrent users or stored records)
• Hardware or resource usage (CPU, RAM, DB storage)

Example:

All input/output screens must load within 3 seconds under normal load (30 concurrent users, Intel i5 server, 4GB RAM, 500GB HDD, 500KB/s connection).

Failing to define these early can lead to major complaints later. Don’t skip this — performance bottlenecks are costly to fix.

3. Usability

Usability focuses on how easy and pleasant it is for users to interact with the system. It can be assessed by five key elements:

• Effectiveness: Users can accomplish what they need without unnecessary steps.
• Efficiency: Fewer clicks, faster actions, clear button labels.
• Engagement: UI design must suit the user’s role and context — not just look “cute.”
• Error Tolerance: Don’t wipe out all input fields when one validation fails.
• Ease of Learning: Consistent layout across forms helps users learn faster.

4. Data Integrity

Integrity ensures that data remains accurate, consistent, and trustworthy at all times — even during batch processing or asynchronous jobs.

If your system sometimes returns the right result and sometimes doesn’t, it’s a nightmare for users and your reputation.

5. Availability

Availability measures how reliably the system can be used:

• Must operate 24/7 with maximum downtime ≤ 1 hour per year.
• Scheduled maintenance: no more than once per quarter.
• Must not depend on any third-party components that can disrupt uptime.

6. Auditability

Audit requirements define what activities must be recorded for verification (not reporting):

• Audit logs stored in a separate database.
• Data backed up daily and retained for 30 days.
• Audit records are read-only from the user interface.

7. External Interface

This refers to integration between systems — APIs, data exchange formats, and synchronization rules.

Examples:

• All data must be exchanged via REST APIs.
• API results must be returned in JSON or XML format.
• Integration frequency and payload details must be documented.

8. User Interface

UI requirements define how the system looks and behaves:

• All grids must support sorting and filtering.
• Deletion actions require confirmation prompts (Y/N).
• Error messages must include recovery guidance.
• Prefer vertical scrolling, limit horizontal scrolling.
• Default resolution: 1024×768 pixels.
• Sequential workflows must include a progress bar.

9. Migration

Migration defines the process of transferring legacy data into the new system.

Example:

Migrate 250,000 customer records, 12,500 products, and 500 pricing tables from the legacy system to the new database.

Never underestimate data migration. It’s tedious, error-prone, and often underestimated by stakeholders.

10. Supportability

Supportability ensures that the system runs well on defined environments — OS, browsers, and hardware.

For instance:

The solution must support Windows 11, macOS, and Chrome v120+.

11. Compliance

Compliance requirements ensure the system follows laws and regulations, including:

• Financial or tax reporting standards
• Data privacy (GDPR, HIPAA)
• Environmental or labor laws
• Corporate branding or security policies

12. Flexibility

Flexibility measures how well the system adapts to different contexts — industries, geographies, or organizational structures.

For example, Microsoft Dynamics 365 is highly flexible, supporting 120+ countries and multiple industries (manufacturing, banking, healthcare, etc.).

13. Scalability

Scalability defines how easily the system can handle increased loads in the future:

• Servers can be upgraded.
• Databases can be split or replicated.
• Load balancers can be applied (e.g., HAProxy).

14. Extensibility

Extensibility focuses on functional expansion — adding new modules without breaking existing ones.

Examples:

• Add a new marketing cost module without altering the old schema.
• Extend inventory tracking without redesigning the core database.

15. Localization

Localization ensures that the system fits local languages, currencies, and regulations.

Examples:

• Support British vs. American English spelling.
• Follow local accounting standards (e.g., USA vs. Venezuela).
• Reflect local cultural preferences in UI and workflow.

16. Purchased Components

If the solution uses third-party components, these must be clearly documented — including license, features, and limitations.

Example: Using a prebuilt loyalty solution as a paid add-on to Dynamics 365 CRM instead of developing from scratch.

17. Maintainability

Maintainability determines how easily the system can be diagnosed and fixed when issues occur.

Examples:

• Quarterly upgrades should take less than 30 minutes.
• Code must follow defined conventions and be peer-reviewed.
• Documentation must cover every module and feature.

18. Safety

Safety requirements ensure that the system doesn’t harm users or the environment.

Example:

In a hospital system, prescriptions must be approved by a doctor before printing to avoid potentially harmful errors.

19. Legal and Copyright

This NFR covers intellectual property and branding:

• All IP generated during development belongs to the client.
• Customer logos must respect official color codes, dimensions, and brand guidelines.

20. Installability

Installability defines how the system can be deployed, upgraded, or uninstalled.

Examples:

• Installation must be performed by a certified administrator with ≥3 years of C# experience.
• Plugin upgrades must not alter existing data structures.

21. Accessibility

Accessibility ensures that the system is usable by people with disabilities.

Examples:

• Provide text transcripts for audio lessons (hearing-impaired users).
• Support voice control for visually impaired users.

22. Reusability

Reusability measures how components can be reused across different systems.

Example:

The FAQ module in one e-commerce project should be reusable in other subsidiaries’ websites.

23. Online Manual

An Online Manual provides built-in, contextual help for users — such as a Help button linking to live documentation or pop-up guides for error recovery.

These 23 Non-Functional Requirements may not always be visible, but they make or break your system’s reliability, scalability, and user experience.

If you’re a Business Analyst or Solution Architect, remember:

Ignoring NFRs is like building a car with a powerful engine but no brakes or seatb