Clear custom software requirements specification is one of the key factors affecting the success of any project. It helps estimate the cost of work, understand the goals, and create a project scope. In this article, we’ll review a step-by-step process of writing this document. After reading the post, you’ll be able to correctly write and structure a simple software requirements document. 

What Is Custom Software Requirements Specification?

Any software development life cycle (SDLC) includes an SRS record that stands for software requirement specification, documentation that contains detailed information on how software should run. It gives a complete overview of functional and non-functional requirements. Usually, business analysts along with team lead developers and project managers are responsible for writing such a paper.

Below is a complete list of information included in any SRS:

  1. Inputs, outputs, behavior.
  2. Criteria to evaluate the operation.
  3. Use cases that define user interaction.

Simply put, SRS describes what an app/system is to do and what it is not to do. It serves as a basis for estimating the cost of the final product, deadlines, risks, timeline, and delivery schedules. The document is preceded by a concept of operations that describes the features of the product from the viewpoint of its users.

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Why You Should Write SRS

The main objectives of writing a software specification are as follows:

  • Providing the basis for cost estimation.
  • Serving as a basis for validation.
  • Facilitating on-time delivery of the project.
  • Defining a testing framework.
  • Giving a basis for future fixes and improvements.

An SRS record can act out as an FSD (Functional Specification Document) or PRD (Product Requirement Document). FSD is responsible for the software part of a new project while PRD contains information about the hardware part.

What Are the Difficulties of Using the SRS?

A well-structured SRS document is the best and the most right basis for contracts between a client and an engineering company. However, a lot of stakeholders ignore the importance of such records. That’s the major concern of most entrepreneurs working in the information technology industry.

Coders explain that the unwillingness to write or use software requirements is caused by the lack of information on how to outline, write, and format the documents of that style. We prepared comprehensive information on writing specs together with a sample outline for you to learn the essentials of tech papers writing.

Diceus team focuses on thorough preparation for the development of a new product to ensure its high performance. We have certified business analysts and project managers that craft informative software requirements specification documents that fully display the scope of the project and show you its functionality. 

How to Write Software Requirement Documentation: Here’re 4 Simple Steps 

We give you a step-by-step guide on how to craft a high-quality SRS document for a new product that will help you eliminate the risks and improve the overall development process.

1. Create an outline

An outline is a plan of your document that contains key points about the product and its scope. You can use it for generating new ideas and organize them in a logical structure. Here’s a sample of an outline.

  • 1. Introduction
  • 1.1. Purpose
  • 1.2. Document Conventions
  • 1.3. Intended Audience
  • 1.4. Product Scope
  • 1.5. References
  • 2. Overall Description
  • 2.1. Product Perspective
  • 2.2. Product Functions
  • 2.3. User Classes and Characteristics
  • 2.4. Operating Environment
  • 2.5. Design and Implementation Constraints
  • 2.6. User Documentation
  • 2.7. Assumptions and Dependencies
  • 3. External Interface Requirements
  • 3.1. User Interfaces
  • 3.2. Hardware Interfaces
  • 3.3. Software Interfaces
  • 3.4. Communications Interfaces
  • 4. System Features
  • 4.1. System Feature 1
  • 4.2. System Feature 2 (and so on)
  • 5. Other Non-Functional Requirements
  • 5.1. Performance Requirements
  • 5.2. Safety Requirements
  • 5.3. Security Requirements
  • 5.4. Software Quality Attributes
  • 5.5. Business Rules
  • 6. Other Requirements
  • Appendix

2. Define the goals

To define the goals of your project, answer the following questions:

  • What is a new product developed for?
  • What kind of value does it bring?
  • Who are the major competitors? Can you make a better product?
  • What are the essential requirements for a future project?

You can sum up the answers and formulate the objectives. It’s good to make a list of people that will have access to the document and how they will use it. You can add BAs, project managers, coders, QAs, people from the client’s side and your sales (marketing) teams.

Use and Audience

During this stage of the SRS writing process, you should decide on who will be able to read and use the SRS documentation. The intended group of people may include test engineers, developers, PMs, and other stakeholders. 

Scope and definitions

The scope should include all the benefits the stakeholders can get with the software under development. It must also describe the general business goals. Add the definitions of the terms you use throughout the document. 

3. Add details to the requirements

There are a few types of requirements that you should add to the document. We can roughly divide them into high-level and low-level ones. Here are the high-level requirements:

  • Business requirements – goals, mission, problems to solve, etc.
  • User needs – the interaction of a user with a new system, functionalities they need.
  • System requirements – functional and non-functional.

Here are the essential low-level requirements:

  • User interface
  • Market specs
  • Stakeholder specs

Let’s take a closer look at system specifications.

Functional requirements

They are the so-called goals of a new system that you’re going to build. It’s a description of a system and its functions that will solve the users’ tasks. There are a few ways to document such specs.

User story

It’s a system requirement that focuses on the people (and their viewpoints) that will use the solution. It’s about the impact and perception. This is a component of epics and initiatives.

Here are the acceptance criteria for a user story:

  • You note down the parameters and boundaries of a user story
  • It’s completed
  • It works as predefined

Have a look at the example of acceptance criteria for a user story:

Possible variants of the acceptance criteria for this user story:

  • Show the balance after successful authentication. E.g: $1,400
  • Show Total balance. E.g: $3,700
  • Display Payment due date. E.g: July the 17th
  • Display Minimum payment due. E.g: $120
  • Display the error message in a case of timeout. E.g: “Sorry, there’s a problem with the service. Please try again later”

Use case diagram

You can define a pack of symbols for marking the users and their interactions with the system:

  • Actors – users that interact with the system.
  • Goals – the results of the use cases.
  • System – displays the interaction.

This will help you build efficient scenarios of user interactions that will guarantee good user experience.

WBS (Work Breakdown Structure)

The main task of this component of the SRS document is to break huge projects into small parts that can be easy to manage and complete. You can divide the whole development process into parts that you will give to several teams at one and the same time. This will lead to easier team management and better productivity.

Visuals / Design

You should know how the app will look. Here you can have a mockup, a wireframe, and a prototype. And here’s the core difference between these issues:

  • A wireframe displays the framework of a new product. You will not find all the visual elements in it.
  • A mockup displays all the colors, schemes, fonts, layouts and so on. It’s static and you cannot click on the elements to see how they work.
  • A prototype is a clickable variant where you can check the way a user can interact with the system. You can test the user journey and detect any problems or drawbacks during the journey process.

With wireframes, mockups, and prototypes, you can turn textual requirements into real representations, visualize, interact with various elements and solicit feedback.

Non-Functional Requirements or NFR

Here are the core components of the non-functional requirements:

  • Usability – how easy it’s to access or use the app.
  • Availability – how the app operates and functions.
  • Scalability – if the app can process the increased number of requests.
  • Performance – how the app reacts to the user’s requests.
  • Reliability – how the app acts out in specific conditions.
  • Security – the way the app protects information.

4. Get an SRS document approved

You should show the document to the people that are participating in the development process. You can make a short presentation for the stakeholders if it’s required. You may have the need to update the document or add any other important issues.

This SRS example will help you structure your own specifications. Besides, we’ve collected useful tips for writing specs.

Key Components of an SRS Document


The introduction contains the following paragraphs: Purpose, Background and Product Overview, References. These are the most common names but you can find analogous headlines in different sources.

The purpose must reflect the main functionalities of the system or product under development.

The background contains all the terms that appear in the text of SRS. Take into account that you must accurately explain every single term that is unclear to avoid misunderstanding.  The more precise your description will be the better.

References are bibliography lists providing links and literature sources you make references to.

SRS introduction example: “The objective of this project development is to design and develop an e-commerce application for the online store selling kids wear”.

Overall Description

This part of a requirement spec is comprised of the following sections: Perspectives, Product Features, Operating Environment, Design Constraints, User Documentation.

Product Features and Perspectives are written to describe the requirements for the final product. Analysts use data flow diagrams (DFD) to show the general interaction within the system. Here is an example of the DFD:

Operating Environment describes the SDE. It includes information about the operating system, compiler versions, databases, servers, software, and hardware, etc.

Design Constraints imposes limitations on the following things:

  • the programming language, databases;
  • coding standards;
  • operational environment;
  • business logic, etc.

User Documentation provides information about the records needed to users. For example, an HTML book.

System/Product Features

This part contains a complete list of product features with the names and detailed descriptions including the priority of implementation, response sequence, functional requirements, etc.

External Interface

This section is about the interaction between the product and the environment (API, different types of data, etc).

Non-Functional Requirements

There are the functionalities difficult to describe as product features. These can be the specs for security and safety. Here is a list of non-functional requirements:

  • Performance
  • Product quality
  • Security


Appendixes usually contain the glossary of some additional terms. It may include the description of the analysis models and diagrams, issues lists, and lists of things to be done in the future.

Methods to Collect Information for SRS

Here are the essential ways for gathering information for the future SRS record:

  • Brainstorming. You will get a list of ideas, problems, tasks that need to be solved. And you will discuss the solutions for each of them.
  • Document analysis. You can view available records like existing business plans, agreements with other vendors, data models and so on.
  • Interface analysis. You will define the functionalities of a user interface and a back-end part of the app.
  • Interview. It’s good to have a list of standard questions for all types of projects and prepare the additional ones for specific products in advance.
  • Prototyping. It will contain the essential functions to show how the product can function.
  • Mind mapping. Build a hierarchy for all the ideas and system components.
  • Focus group. You get feedback from the users’ representatives to understand their needs, requirements, and if the app can solve them.
  • Requirements workshop. It’s a discussion of the cross-functional requirements of a new product.

SRS Writing Rules

Any type of writing requires adhering to some rules and recommendations. You might find our recommendations helpful for business analysis and specs writing.

  1. Allocate enough time for the SRS outline.
  2. Keep information precise and clear.
  3. Assign SRS writing to a business analyst or another specialist different from programmers.
  4. The person writing software requirements specifications should have a good command of English if you deal with international projects.
  5. Along with diagrams, use different tables and charts.
  6. Pay due attention to the most difficult tasks.
  7. Keep the document up-to-date and edit it every time you make the changes. Depending on the format type of your records, you need to know how to correctly edit the paper. Let’s say, you saved your SRS as a PDF file, then you need to know how to edit a PDF.
  8. Write with regard to the fact that the product will be tested in accordance with the SRS.
  9. Avoid ambiguity.
  10. Avoid writing too many details if the requirement is a well-known feature.

Need help with software requirements specifications? Our experts are skilled in outlining and structuring project documents. 

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