TLDR: How exactly the system must achieve the requirements

Specifications are the detailed descriptions of both functional and non-functional requirements. They translate high-level requirements into precise, actionable guidelines for developers and testers. Specifications clarify the behavior of the system and how to achieve desired performance or standards.

For functional requirements: A specification might describe exact input formats, error handling, and expected outputs. For example, a specification for the login feature could specify that the system must validate user credentials against a database and display an error message for incorrect logins.

For non-functional requirements: A specification might define measurable goals such as "the application must process 100 transactions per second" or "encryption must be AES-256."

Spell: Software Engineering and Architectures