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.
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.
An Software Requirements Specification document should describe:
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:
Lower-level 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:
Introduction:
Functional Requirements:
Non-Functional Requirements:
Reference System Architecture
Data Requirements:
Integration Requirements:
User Requirements:
Project Constraints and Assumptions:
Appendices:
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:
Examples of business requirements for a new FinTech platform may include:
TL:DR: The business requirements section summarizes the reasons for initiating the project and documents the expected commercial benefits.
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:
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.
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:
As you can see from the above example, the use case specification includes:
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.
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 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:
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:
The common types of acceptance criteria for user stories include:
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 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 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:
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 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:
Consult with technical specialists such as Solution Architects and IT infrastructure engineers to correctly capture and outline all the scalability requirements for software development.
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:
This section may also include more specific security requirements, mandated by regulations such as PCI DSS, HIPAA, and GDPR among others.
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:
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.
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:
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 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:
Clear data requirements help establish better data quality, clear data lineage, and greater system interoperability.
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!
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:
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.
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:
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.
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:
Finally, make sure all the information is accurate, complete, and easily verifiable.
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:
Also, ensure that all requirements also have acceptance criteria. Check that the set requirements are testable.
Once you’re done with writing the bulk of the software specifications, switch to the editing mode.
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.
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.
