Functional specification

A functional specification is a document in systems engineering and software development that outlines the functions a system or component must perform, typically forming part of a broader requirements specification and building on the results of requirements analysis. It describes what users need from a system and the required properties of its inputs and outputs, without defining implementation details or how the system works internally, focusing instead on external interactions, for example stating that clicking a button closes a dialog and returns focus to the main window. The document serves developers by communicating what must be built, testers by defining what tests should validate, and stakeholders by clarifying what they will receive, letting teams reach agreement before committing resources to coding and testing. It functions as the more technical counterpart to a matching requirements document, helping negotiate a cost effective way of meeting the software requirements. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/