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Functional requirements
A functional requirement describes something a product must do: a specific behavior, feature, or response to a given input. Functional requirements define what the system delivers to its users, such as processing a payment or generating a report, and together they describe how the product is meant to behave in practice.
What it means
Functional requirements are the 'what it does' half of a specification. Each one states a behavior the system has to provide, ideally clearly enough that a developer can build it and a tester can check it. 'The system shall email a receipt after each successful payment' is functional. It names an action, a trigger, and an expected result.
They pair with non-functional requirements, which cover how well the system does those things, like speed, security, and reliability. Keeping the two apart matters, because a feature that works but is painfully slow still fails its users. Teams usually capture functional requirements as user stories or requirement statements and trace each one to the tests that prove it works.
In practice
For an online banking app, 'a user can transfer money between their own accounts' is a functional requirement, because it describes a concrete capability. The related non-functional requirement might say that transfer must complete within three seconds, which is about quality rather than the capability itself.
Foire aux questions
What is the difference between functional and non-functional requirements?
How do you write a good functional requirement?
Manage requirements the modern way
Modern Requirements brings documentation, traceability, and reviews together inside Azure DevOps.
