What Is a Functional Requirement? | Vantage
Functional Requirement A functional requirement describes a specific behavior or function of a system: what it must do, what inputs it accepts, and what outputs it produces. Functional requirements define the features and capabilities that users interact with. They answer the question: "What does the system do?"
Why functional requirement matters
Functional requirements define the scope of what engineering builds. Missing functional requirements mean missing features. Vague functional requirements mean features that do not match the PM's intent. Clear functional requirements align the team on exactly what will be built.
How it works
Each functional requirement follows a pattern: "The system shall [verb] [object] when [condition]." Example: "The system shall display a list of matching projects when the user enters a search query of 3 or more characters." Functional requirements are testable: you can verify whether the system does or does not satisfy each one.
Common mistakes
Confusing functional requirements with implementation details ("use React" is not a functional requirement)
Writing requirements that are not testable
Mixing functional and non-functional requirements in the same list
Not specifying edge cases and error handling
Requirements that are too broad ("the system shall be easy to use")
Related terms
How Vantage relates
Vantage extracts both functional and non-functional requirements from PRDs automatically. Each functional requirement is tagged with priority and effort, enabling clear prioritization of what to build first.