Requirements specs for web applications: content and structure
A requirements spec for a web application describes what the system must do and under what conditions. Beyond the functions, you need web-specific requirements: which browsers to support, user roles and permissions, performance under load, and integrations with existing systems – plus clear boundaries for what's out of scope.
A requirements spec for a web application is the difference between commissioning something predictable and hoping for the best. But a web app has requirements an ordinary program doesn’t – browsers, concurrent users, integrations. Here’s what the spec should include and how to keep it from growing out of control.
Web-specific non-functional requirements
Most people can list what an application should do. What’s more often forgotten are the requirements for how well it should do it – the non-functional requirements. For a web application, those are exactly the ones that matter most, since they arise from the fact that the service runs in a browser for many different users at once.
A checklist of what should be included:
- Browser and device support. Which browsers need to work, and should the application be usable on mobile and tablet, or mainly on desktop?
- Performance under load. How fast should pages respond, and how many concurrent users should the system handle without slowing down?
- Security. How are login, passwords, and sensitive data handled, and what requirements apply around data protection?
- Accessibility. Should the application meet an accessibility standard, and if so, which one?
The point is that these requirements have to be stated explicitly. If it doesn’t say the application must handle hundreds of concurrent users, nobody has built for it – and in the worst case, that’s only discovered once the traffic arrives.
Roles and permissions, made clear
A web application almost always has different types of users: a regular user, an administrator, maybe a read-only guest. Who gets to see and do what is one of the most common sources of misunderstanding, and therefore worth documenting clearly.
The key is to describe roles in terms of what they should be able to do, not in technical jargon. A simple and effective approach is a table that maps roles against functions, so that even a non-technical decision-maker can see at a glance who gets what.
| Role | Allowed to |
|---|---|
| Guest | Read open content, cannot log in |
| User | Log in, manage their own data |
| Administrator | Manage all users and content |
With the roles written down this way, permissions stop being guesswork during development. Everyone – client and developer – works from the same picture of who gets to do what.
Performance and integrations
Two web-specific areas deserve special attention, since they’re often underestimated.
Performance under load is about how the application behaves when it’s used for real. A page that’s fast for a single tester can become unusably sluggish when a hundred people are on it at once. The requirements spec should therefore state an expected load and how the system should respond to it – otherwise there’s nothing to build or test against.
Integrations are connections to systems that already exist: an ERP, a payment service, a login system. Each integration is its own small subproject with its own testing, and they tend to get more complex than they first appear. A concrete example: a web app that shows real-time stock levels is entirely dependent on a reliable connection to the inventory system – if that doesn’t work, the rest of the application matters less. Dependencies like that belong in the spec from the start.
Boundaries that keep scope creep out
Perhaps the most important part of a requirements spec isn’t what’s included, but what isn’t. Without clear boundaries, the scope creeps upward – small additions that each seem reasonable but together blow both the budget and the timeline. It’s called scope creep, and it sinks more projects than technical problems do.
The countermeasure is simple but underused: an explicit list of what’s outside the project, plus an agreed process for how changes and additions get handled when they come up. That turns every new request into a deliberate decision with a price tag, instead of something that slips in unnoticed. A good spec, then, sets both the boundary and the rules for how that boundary can change.
Finding the right level of detail is an art in itself – too little and you build the wrong thing, too much and you lose flexibility. A short discovery phase is often the best way to land in the right spot. Want help producing a requirements spec that holds up? That’s part of our services. Get in touch and we’ll look at what your project needs.
Frequently asked questions
What's the difference between functional and non-functional requirements?
Functional requirements describe what the system must do – which actions the user should be able to perform. Non-functional requirements describe how well it should be done: performance, security, accessibility, and browser support. For a web application, the non-functional requirements are often the ones that get forgotten, even though they largely determine whether the result is usable.
What web-specific requirements does a web app spec need?
Which browsers and devices need to be supported, how the application should behave on mobile, performance when many people use it at once, security around login and data, and integrations with existing systems. These are requirements that don't arise for a desktop program but are completely central on the web, and they should be spelled out explicitly in the spec.
How do you document user roles clearly?
Describe each role in terms of what it can and can't do, not in technical permissions jargon. A simple table mapping roles against functions makes it clear to everyone, including non-technical decision-makers. The point is that everyone understands who gets to see and do what, so permissions don't turn into guesswork during development.
What is scope creep and how do you prevent it?
Scope creep is when the scope slowly grows over the course of a project through small additions that each seem reasonable but together blow the budget and timeline. It's countered with clear boundaries in the requirements spec – an explicit list of what's out of scope – and an agreed process for how changes are handled.
Do you need a complete requirements spec before development starts?
Not necessarily down to the smallest detail, but the main outlines should be clear: purpose, roles, the most important flows, web-specific requirements, and boundaries. A common mistake is either specifying too little and building the wrong thing, or locking down every detail in advance and losing flexibility. A discovery phase helps you find the right level for your specific project.