How to write a software requirements document

A software requirements document describes who will use the software, what each of them needs to do, which systems it connects to, and what is deliberately left out, in language a non-developer can check. For most business projects, 5 to 15 pages is enough. The test of a good one is simple: if you gave it to two different development teams, they'd build roughly the same thing and quote within a sensible range of each other.

You don't need to know how to code to write one. You need to know your business, and be willing to write down the boring details that live in your head.

Why the document matters more than the contract

Most software disputes aren't about bad code. They're about two people who read the same sentence and pictured different things. "Customers can track their orders" might mean a status label, or a live map with a courier's location. One takes an afternoon to build. The other takes weeks.

A requirements document turns those assumptions into text you can point at. It also makes quotes comparable. When one studio quotes $25,000 and another $70,000 for "an ordering app", you can't tell who is being realistic. When both quote against the same document, the gap usually shrinks, and the remaining difference tells you something real about each team.

It's also the cheapest place to change your mind. Rewriting a paragraph costs nothing. Rewriting a feature after it's built costs money.

The sections to include

Here's the structure we recommend. Skip sections that don't apply, but think about each one before you do.

1. Summary and goal

Two or three paragraphs: what the software is, who it's for, and what should be different for the business once it exists. Include a number if you can. "Cut order processing from 20 minutes to 5" gives the team something to design toward.

2. Users and roles

List every type of person who touches the system: customers, staff, managers, admins, partners. For each, write what they're allowed to see and do. Permissions are one of the most commonly forgotten details, and one of the most expensive to add later.

3. What each user needs to do

This is the heart of the document. Write it as short user stories: "As a warehouse manager, I want to see all orders that need packing today, sorted by courier pickup time, so I can plan the shift."

Then mark each one as must-have, should-have or nice-to-have. Be honest. If everything is a must-have, nothing is, and your first version will be late.

4. Screens and flows

A rough sketch of each screen helps more than any amount of text. Photos of whiteboard drawings are fine. So are screenshots of other apps with notes like "like this, but with our filters".

Describe the main flows step by step, including what happens when things go wrong. What does the user see if payment fails? If they lose signal halfway through a form? These edge cases are where estimates drift.

5. Data and integrations

List what information the system stores and where it comes from. Then list every outside system it talks to: payment gateway, accounting software, CRM, SMS provider, shipping partner, existing databases. For each integration, note whether data flows one way or both ways, and how often.

6. Non-functional requirements

These describe how the software behaves, not what it does:

• How many users at once, and how fast pages should load

• Which devices and browsers must be supported

• Languages and currencies

• Security and compliance needs, such as India's DPDP Act or GDPR for European users

• Backups, uptime expectations and support hours

7. Out of scope

Write down what this version will not do. "No mobile app in phase one. No multi-currency. No customer loyalty points." This list prevents more arguments than any other section.

8. How success is measured and accepted

Say who will test the finished software, what they'll test against, and how long they have to report problems. Add one or two business measures you'll check after launch.

Mistakes that make documents useless

Some documents are long and still don't help. The usual reasons:

• Describing solutions instead of problems. "Use a microservices architecture" is the team's job to decide. "Handle 5,000 orders on sale days" is yours to state.

• Vague words. "Fast", "user-friendly" and "secure" mean nothing until you attach a number or an example.

• Copying a competitor wholesale. Their app has features built for their business model. Pick the three things you actually need.

• Writing it alone. Ask the people who'll use the software daily. They know the steps that managers forget.

When to get help writing it

If your project is simple and you know the process well, write the first draft yourself. You'll learn a lot about what you really need.

If the project involves several user types, integrations with older systems, or anything with money or personal data, a short paid discovery phase with the team that will build it is often worth it. They know which questions change the price, and they'll ask them. We run this as the first step of every custom software project, and we explain how it fits with pricing in fixed price vs time and materials.

Questions about software requirements documents

How long should a software requirements document be?

Long enough that two teams would build the same thing from it. For most small and mid-size business projects that's 5 to 15 pages, plus sketches. Complex platforms need more, but length isn't the goal. Clarity is.

What is the difference between an SRS and a PRD?

An SRS (software requirements specification) tends to be detailed and technical, often used in formal contracts. A PRD (product requirements document) focuses on users, problems and goals. For most business projects, a plain-language document that covers both is what you need.

Do I need a requirements document for an MVP?

Yes, but a lighter one. An MVP document should be ruthless about scope: the few flows that prove your idea works, and a clear list of what waits for version two.

Who owns the requirements document?

You do. It describes your business needs, and it should be yours to share with any team you choose. Make sure your contract says so if a studio writes it for you during discovery.

Turn your notes into a quote

Have a rough document, or just a page of notes? Send it to us. We'll point out the gaps that would change the price, and if we're a good fit, come back with a written scope and a fixed quote.