Non-Functional Requirements
A non-functional requirement (sometimes called a quality attribute, or NFR for short) does not describe what the product does, but how it must behave while doing it. Besides stories, a real backlog contains defects, technical work, regulatory obligations, and precisely these constraints; forcing them into the story mold produces the fictions of the fake user.
Why they don't fit in an individual story
"As a user, I want the page to load quickly" has no beneficiary distinguishable from that of any other story, nor does it fit in a sprint: it is a system constraint, not a slice of value that can be prioritized against another. Entering it as a story causes two kinds of harm. On the one hand, it cannot be ordered by value, because it affects everything. On the other, it is confirmed only once, when in fact performance or accessibility degrade with every change and must be verified continuously.
Where Each One Goes Based on Its Scope
The deciding factor is the scope of the quality:
- General system quality (overall performance, accessibility, encryption): it belongs in the Definition of Done or in a cross-cutting constraint, and is verified in every increment.
- Threshold specific to one piece of functionality (a response time particular to this screen): here it is indeed an acceptance criterion of that specific story.
The same logic separates acceptance criteria from the Definition of Done: if something must be met in everything that is delivered, it goes in the DoD; if it is specific to this need, it is a criterion. When the non-functional requirement is an obligation with enforceable evidence (a regulation that requires traceability and approval), it is treated as regulatory compliance, with an identifiable owner.
Common mistake
Adding non-functional requirements as stories. "As a user, I want the page to load fast" has no distinguishable beneficiary and doesn't fit in a sprint. Confirming a constraint only once is just as dangerous: performance and accessibility degrade with every change, so they belong in the Definition of Done or in a cross-cutting constraint, verified in every increment; only a threshold specific to a particular feature is an acceptance criterion of that story.
Resources
🏦 Skill User storiesState of the art and development guide · Skill Arena
📄 Historias de usuario v.5.0 [User Stories v.5.0, in Spanish]Free download · Scrum Manager · Jan 2026
📄 Scrum Master en equipos con IA v.1.0 [Scrum Master in Teams with AI v.1.0, in Spanish]Free download · Scrum Manager
References
- Cohn, Mike. (2004). User Stories Applied (chapter on non-functional requirements). Addison-Wesley.
- Schwaber, Ken; Sutherland, Jeff. (2020). The Scrum Guide.
See also
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