Software requirements specification (SFS) describes the functionality the software needs to meet all stakeholders’ needs, how it should operate, and in what way it should be developed. In most cases, software requirements for app development consists of three core parts: business requirements, user requirements, and system requirements. Each part describes the project from its side: business requirements include information about the project vision, objectives, financial part, etc.; user requirements document data received from potential software consumers; system requirements describe technical part of software development: programming languages used, technologies implemented, third-party APIs, possible system restrictions, etc.