When you have a great product idea or a strong internal driver, it’s tempting to get straight down to action — coding that is. But when you haven’t fully thought through how your application will function, how will you know what features to develop and how will you manage the users’ expectations?
Failure to account for specific user preferences can lead to poor product adoption. And incomplete technical requirements can extend project timelines and budgets.
Software requirements specification describes what the new product should do and which characteristics it must have to be considered successful.
In this post, we explain how to collect, write, and validate requirements for software. We cover functional, non-functional, and technical requirements gathering and documentation, plus provide some best practices for organizing the writing process.
What is a Software Requirements Specification (SRS)?
A software requirements specification (SRS) is a document that outlines the behavior, features, and performance criteria of new software. It acts as a blueprint for initial project scoping, estimation, and timeline planning.
By investing time in writing detailed software requirements, you can avoid costly re-dones and omissions at the later stages of the development cycle. A software requirements specification document also provides a solid basis for estimating the project costs and schedules.
Finally, a software requirements document helps coordinate the development work. It establishes the common “reference baseline” for the products’ capabilities and helps circulate this knowledge among your in-house engineering talent or an external software development team.
What to Include in a Software Specification Requirements Document?
An Software Requirements Specification document should describe:
- The product’s purpose and include justifications for its creation
- All user and project stakeholder requirements
- Features or functions of your future software
Depending on the complexity of your product idea, your software requirements specification document may be just under one page or span over a hundred. For more complex software engineering projects, it makes sense to group all the software requirements specifications into two categories:
High-level requirements:
- Business requirements (e.g. business goals, objectives, and needs)
- User requirements (what the user needs the product to do)
- System requirements (functional and non-functional ones)
Lower-level requirements:
- Stakeholder requirements
- UI requirements
- Performance requirements
- Security requirements
- Market requirements
- Implementation requirements
This structure helps ensure that all requirements are well-documented and can be easily cross-referenced when needed. Here’s how the above SRS format looks in practice:
Sample Software Requirements Specification (SRS) Document Format
Introduction:
- Overview of the software project
- Business goals
- Project objectives
Functional Requirements:
- Use cases or user stories
- User input and output specifications
- System behavior in response to specific inputs
Non-Functional Requirements:
- Product performance requirements
- Security and authentication requirements
- Scalability and reliability criteria
- Usability and user interface design guidelines
- Regulatory and compliance requirements
Reference System Architecture
- High-level system architecture diagrams
- Key software components and modules
Data Requirements:
- Data models, schemas, and data flow diagrams
- Data storage and processing methods
- Reference data architecture
Integration Requirements:
- Types of internal system integration required
- Types of third-party system integration required
- Authentication methods used for each system
User Requirements:
- User roles and permissions
- Standard user workflows
- Reference user interfaces
Project Constraints and Assumptions:
- Constraints and limitations of the software
- Assumptions made during requirement gathering
Appendices:
- Extra information such as glossary, abbreviations, or additional diagrams.
Business Requirements
Business requirements define high-level commercial objectives, needs, and constraints for the project to be considered valuable for the company.
A business requirements section includes:
- Reasons for initiating the project
- Market and customer research
- Goals and objectives to be met
Examples of business requirements for a new FinTech platform may include:
- Revenue diversification: “The new robo-investing functionality will attract extra users to the product and help generate more transactional revenues.”
- Customer retention: “A new chatbot interface will help users discover more product features and resolve common queries through self-service. It also provides new opportunities for in-app engagement”.
- Competitive advantage: “With a new data processing architecture, we can deploy self-service analytics tools for financial advisors such as next-best-action models to differentiate better over competition”.
TL:DR: The business requirements section summarizes the reasons for initiating the project and documents the expected commercial benefits.
Functional Requirements
Functional requirements provide a clear, coherent, and consistent description of the products’ features, capabilities, and expected behaviors. They are mostly about how the system will cater to different user actions such as account registration, data input, payment processing, etc.
High-level functional requirements describe the general product feature or standard user flows. For example:
“A user must have the option to create a free account using single-sign-on. After the general information is provided, the system must offer to start a free 7-day trial or select a premium plan”.
On the lower level, functional requirements document the exact system response to a particular user action. For example:
“The system automatically sends a confirmation email to validate new account creation.”
“The option to start a free trial is available only to people with previously unused emails and full name combinations.”
To better convey your idea, you can document functional requirements as a combination of flow charts/diagrams and step-by-step feature descriptions as shown in the example below:
Source: Academia
How to Write Functional Requirements for Software
The standard approach to documenting functional requirements is by describing the set of product use cases at a high level and associated user stories at a lower level.
Use Cases
A use case specification describes a sample product usage scenario for a specific actor (type of user) and details a sequence of events within this scenario.
For example, a use case specification for a login flow can look like this:
Source: ResearchGate
As you can see from the above example, the use case specification includes:
- Use case name and description
- Pre- and post- interaction condition
- Basic interaction path
- An alternative path
An extra way of documenting use cases is via diagrams. Use case diagrams provide a sample user flow, visualizing how your application interacts with the user, organization, or external services.
Source: Lucidcharts
Similar to text-based use case specifications, use case diagrams help document the goals users (actors) try to achieve. Diagrams are handy add-ons to text descriptions as they help showcase the scope of the system and visualize different goals of system-user interactions.
By describing your system through different use cases, you have a better chance to ensure the completeness and non-redundancy of requirements. Use cases, combined with business requirements, also help the software development teams determine the optimal technical characteristics for the system later on.
User Stories
User stories are a popular Agile technique for documenting functional requirements. As the name suggests, it’s a short software description, created from the perspective of the end user.
The standard user story format is:
As a < type of user >, I want < some goal > so that < some reason >.
User stories help better capture the users’ goals and needs. They also explain the rationale behind certain actions, highlighting which features must be included in the software.
Each user story also includes a set of acceptance criteria — a formal list of specific, measurable conditions or requirements that must be met to mark a user story as complete. User stories can be engineered in different ways. Acceptance criteria narrow down the scope of possibilities.
For example, the acceptance criteria for a login feature might be as follows:
- “User can use an email or a mobile phone number to log in”
- “The lengths of the password should be between 6 and 20 symbols”
- “Symbols in a password may include letters, numbers, and special signs”.
The common types of acceptance criteria for user stories include:
- Given-When-Then scenarios, which validate if the user achieves the desired outcome(s).
- Rule-based acceptance criteria, based on specific functional or behavioral parameters
Without clear acceptance criteria for user stories, you’ll struggle to validate the end product against the initial requirements at the user acceptance testing stage. In addition, acceptance criteria also help set clear expectations for the development team, facilitate feature prioritization, and help with scope control.
Non-Functional Requirements
Non-functional requirements define how your system should perform in terms of reliability, security, usability, and other quality criteria. Effectively, they document how the software must function, rather than what it should do.
The common examples of non-functional requirements include:
Performance
Performance requirements describe how well a system must operate under certain conditions (e.g., peak traffic, limited bandwidth, or in normal conditions).
A standard software project specification typically includes the following performance requirements:
- Max/min satisfactory response time for different types of user interactions
- Typical throughput time under normal conditions
- Size and timing of maximum-throughput periods
- Min/max storage capacity per system
Many of the system performance characteristics are driven by existing or expected customer service level (SLA) agreements. For example, Google SLAs state that its App Engine Service will provide a monthly customer uptime of at least 99.95%. Therefore, any new SRS document for this product would likely reference an equivalent performance requirement.
Pro tip: Consider system dependencies when deciding on appropriate performance requirements. For example, relational NoSQL databases allow faster processing speeds, while SQL ones offer higher data integrity. Therefore, two different data analytics projects, built atop these systems will inherit the technologies’ respective strengths and shortcomings.
Scalability
Scalability requirement defines how the system will respond to increased usage and which mechanisms are in place to accommodate higher loads (e.g., more users, more data, etc). Scalability can be defined both on hardware and software levels.
For example, you can document requirements for:
- Data compression
- Extra on-premises CPU usage
- Automatic cloud instance scaling
- Proper disk space allocation
Consult with technical specialists such as Solution Architects and IT infrastructure engineers to correctly capture and outline all the scalability requirements for software development.
Security
In the past, many engineering teams treated software security as a “bolt-on” — something you do after the first release when the product is already in production. Such an approach, however, proved to be unsustainable. According to the Veracode State of Software Security 2023 report, over 30% of applications have security flaws at the first scan, and 70% contain security vulnerabilities after five years in production.
Because a company’s trustworthiness and security are interrelated, you should always consider security upfront.
Security requirements define different policies, practices, and system design methods for the prevention of unauthorized access and usage. Mostly, these requirements document:
- Desired data security methods (e.g., data encryption, permission access, etc).
- Identity and access management (IAM) controls
- Authentication methods for users and other subsystems/modules
- Intrusion detection and prevention mechanisms
- Data backup and recovery methods
This section may also include more specific security requirements, mandated by regulations such as PCI DSS, HIPAA, and GDPR among others.
Usability
User experience (UX) has become a core differentiator for software products. Design-driven companies grow 2X faster compared to industry peers.
Usability requirements document the system’s ability to provide an intuitive, efficient, and delightful experience for end-users. Typically, this set of non-functional requirements will describe:
- Product navigation
- Interface design
- Accessibility
- Error prevention
- UI personalization
On top of that, you may also want to quantify some of the above criteria. For example, prove navigation design effectiveness by establishing a minimum number of attempts a user needs to complete one use story.
Interoperability
Few software development projects are created in a vacuum. In most cases, new solutions are designed to fit into a wider tech ecosystem.
Interoperability requirements specify how the new software will be designed to interact with other assets in your technical portfolio (e.g., perform write or read operations, automatically synchronize data records, etc).
The common interoperability requirements for software include:
- Cross-platform compatibility (e.g., across browsers and operating systems)
- Database compatibility requirements
- Third-party software compatibility
- Compliance with specific industry standards (e.g., EDI)
- Integration with popular cloud service providers (CSPs)
Systems with high interoperability reduce vendor lock-in risks, are easier to scale, and have fewer maintenance overheads. Moreover, they also help cultivate a data-driven culture by diminishing data silos and data redundancy.
Data Requirements
Data analytics has become one of the key technologies for fast, commercial growth. Over 80% of businesses recognize the strong potential of using big data analytics for improving business efficiency and performance.
Data requirements describe how the software system will retrieve, exchange, manage, and store data. Data requirements typically cover the new applications’ database design and integrations with other elements of data management strategy.
Examples of data requirements for software include:
- Data standards (schema, ranges, allowed values, etc).
- Data quality and validation rules
- Metadata management practices
- Data storage and retrieval mechanisms
Clear data requirements help establish better data quality, clear data lineage, and greater system interoperability.
How to Write Specifications For a Software Development Project: Best Practices
Now that you have a structure for your software specifications document, let’s get down to the deets. Here’s how to write software requirements that get read, understood, and effectively implemented!
Approach the Right Stakeholders
Great software specifications are centered around user needs — and user knowledge rests with multiple stakeholders.
To answer the fundamental question of “who this product is for?” and “why it is needed”, you should engage the following stakeholders:
- Direct users: People who will interact with the new product the most. These can be both internal users and/or external participants, recruited to participate in user research.
- Indirect stakeholders: People who’d be impacted by the developed software. For example, a new payment processing app will impact the process flows across the Financial, Compliance, and Security departments.
- Beneficiaries: Any other people who will derive benefits from the new software. In the case of a payment processing app, that could be Sales specialists, customer support staff, etc.
- Project team: Product owner and senior engineering talent, who’d be able to “translate” the business requirements into functional and non-functional characteristics, plus advice on the optimal tech stack.
To keep the requirements-gathering process streamlined, you can collect some inputs via a questionnaire and invite a smaller group of people to requirements-gathering workshops. Workshops are typically led by business analysts (BAs), who are trained to elicit and clarify requirements in a structural manner. Then organize them into a coherent SRS document.
That said, requirements gathering and formalization can be an intensive project. Especially, when you lack customer knowledge, struggle with assessing the projects’ technical feasibility, and looking to enter a new market.
At 8allocate, we guide clients through the above challenges as part of our product discovery service. By combining interactive workshops with a wider market, customer, and competitor research, we help companies create comprehensive software specifications and transform these into viable digital products.
Apply the Least Work Principle
When writing specifications for software, always keep this principle in mind:
Do not do any work that costs you more than it is worth to you.
What we mean by this is that you don’t have to create an exhaustive, one-hundred-page-long SRS document for every software engineering project.
An SRS document makes sense for:
- Large applications: (Multiple interfaces, 20+ features, integrations with other systems).
- Critical business applications: (Core banking system, online reservation module for a hotel chain, etc).
If you’re considering a proof of concept (PoC) or minimal viable product (MVP), a shorter requirements document, listing key business, functional, and non-fuctional specifications would do. Or even a collection of prioritized use cases and user stories.
Use Accessible, Implementation-Neutral Language
An SRS document will be read by multiple people — ranging from beneficiaries and secondary stakeholders to software development team members. Ambiguous, superfluous, or overly complex language means that some important details will be misunderstood or overlooked.
Good quality software specifications must be:
- Explicit: Don’t make things sound more complex than they should. Avoid terminology and unnecessary acronyms. Use diagrams, models, and schemes to break down more complex ideas.
- Measurable: Create clear boundaries between different tasks. Include quantifiable metrics where possible. Without clear definitions of done (DoD), the team will struggle to validate and verify the end product against the original specifications.
- Flexible: State what the system should do, rather than how it should do it. This way you give the development team more space to come up with the optimal tech solutions to the problem, rather than blindly following an instruction.
- Viable: Verify that all the system requirements can be fulfilled within the outlined budget and timeline. Make sure there are no contradictory requirements or those with technical implementation constraints.
Finally, make sure all the information is accurate, complete, and easily verifiable.
Refine and Decompose More Complex Requirements
Work from the top to bottom. Spell out all high-level functional requirements at first. Analyze that these are feasible and aligned with the limitations of the current program (e.g., budget or human resources).
Then use functional or object-oriented analysis to formalize lower-level requirements for each of the system’s components. You can group the system requirements by initiatives, epics, and stories or create another taxonomy category (e.g., by product subsystem).
In either case, each lower-level requirement must:
- Be written as a single definitive statement
- Have a reference number for tracking purposes
- Be traceable to a higher-level requirement
Also, ensure that all requirements also have acceptance criteria. Check that the set requirements are testable.
Check For Consistency
Once you’re done with writing the bulk of the software specifications, switch to the editing mode.
Check for any:
- Redundancies
- Contradictions
- Compatibility issues
The SRS document must not have any conflicting statements in terms of required quality or performance characteristics. If there are some conflicts, consider the trade-offs between different requirements and select the better option.
Finally, verify the completeness of the document. Did you describe all high-level requirements as lower-level ones? Are there any orphaned specs? If all looks good, your SRS is ready for sign-off.
Conclusions
Detailed software requirements help establish the scope of work so that the project manager can accurately estimate the project timelines, prioritize backlog, and create effective Sprint plans.
The SRS document also acts as a “reality-check” for all the done work. It helps ensure that the developed product meets both the business goals and the identified user needs. Changes made to software in the last stages are both costly and difficult to implement. SRS document helps prevent costly reworks and helps ship software faster.
And you can kick off your software development event faster by partnering with an experienced software development vendor. At 8allocate, we help global teams launch products that hit all the user requirements and generate proven ROI for the business.
Contact us to learn more about our product discovery and software engineering services.
Frequently Asked Questions
Quick Guide to Common Questions
What is a Software Requirements Specification (SRS), and why is it important?
An SRS is a document that defines a software system’s features, behavior, and performance expectations. It acts as a blueprint for development, ensuring clear communication between stakeholders, preventing costly reworks, and setting measurable project goals.
How do I structure a Software Requirements Specification (SRS) document?
A standard SRS document includes business requirements, functional and non-functional requirements, data requirements, system architecture, integration specifications, and constraints. It should be organized for easy cross-referencing and scalability.
What’s the difference between functional and non-functional requirements in an SRS?
- Functional requirements define what the system must do (e.g., user authentication, payment processing).
- Non-functional requirements specify the system’s performance (e.g., scalability, security, performance under load).
How do I ensure my SRS document is clear and effective?
- Use simple, unambiguous language and avoid technical jargon.
- Define measurable acceptance criteria for each requirement.
- Ensure consistency and check for redundancies or contradictions.
- Include diagrams and structured formats to enhance clarity.
What are common mistakes to avoid when writing an SRS?
- Vague or incomplete requirements that lead to misinterpretation.
- Ignoring scalability and security concerns during early planning.
- Overloading the document with unnecessary technical details.
- Lack of stakeholder input, leading to missing user expectations.
How do user stories and use cases fit into an SRS?
User stories provide a user-centric view of system functionality, focusing on goals and expected outcomes. Use cases outline specific interaction flows between users and the system, detailing step-by-step actions. Both approaches ensure requirements align with real-world user needs.
How do I validate software requirements before development?
- Conduct stakeholder reviews and feedback loops.
- Use prototyping and wireframes to visualize key functionalities.
- Perform requirement traceability analysis to ensure all business needs are met.
When should I use a detailed SRS versus a lightweight version?
A full SRS is essential for large-scale, critical systems with complex integrations. A lighter version with key functional and non-functional requirements is sufficient for MVPs, proofs of concept, or agile projects.
What role does an SRS play in Agile development?
While Agile emphasizes iterative development, an SRS still serves as a living document to align stakeholders, define system scope, and guide sprint planning while allowing flexibility for changes.
How does 8allocate support teams in writing an effective SRS?
8allocate provides product discovery, requirement gathering, and software engineering expertise to ensure your SRS aligns with business objectives, technical feasibility, and scalability needs.
