How to Write a Software Requirements Document | Template

How to Write a Software Requirements Document (with a Free Template)

A software requirements document is a written spec that describes what a piece of software must do, who uses it, how it should behave under load, and where it connects to other systems. Get it right and you hand your development team a clear blueprint — and you hand any custom software development shop the exact input they quote from. Get it wrong and you get a fuzzy estimate, a padded budget, and scope creep that shows up in month two.

We write and review these for a living. Most requirements documents we see fail for the same handful of reasons, and most of them are fixable in an afternoon. This guide gives you a copy-ready template, real examples of good and bad requirements, the BRD-vs-SRS distinction that confuses half the founders we talk to, and the specific mistakes that inflate a quote.

What a software requirements document actually is

Strip away the jargon and it’s an agreement. It says: here is the problem, here is what “solved” looks like, here is what we’re deliberately not building. Everyone — you, your stakeholders, the engineers — points at the same page and nods.

The formal version is called an SRS (Software Requirements Specification). You don’t need to obsess over the acronym. What matters is that the document does three jobs:

• Describes behavior precisely enough that two different developers would build roughly the same thing.

• Draws a hard line around scope, so “can we also add…” becomes a change request, not a Tuesday surprise.

• Serves as the reference when someone quotes the work. A vendor reading a tight spec gives you a tight number. A vendor reading three vague paragraphs gives you a wide range — and wide ranges always resolve upward.

That last point is the one people underestimate. Your requirements document is a procurement asset. It’s the difference between “we’ll figure it out as we go” pricing and a fixed, defensible estimate.

BRD vs SRS — and why you might need both

This trips people up, so let’s be blunt about it.

A BRD (Business Requirements Document) answers why. It’s the business case: the problem, the goals, the market, the ROI. It’s written for executives and stakeholders. “We’re losing 15 hours a week to manual invoice reconciliation, and it costs us roughly ₹4 lakh a month in labor and errors.”

An SRS answers what and how the software behaves. It’s written for the people building the thing. “The system shall auto-match incoming invoices to purchase orders using vendor ID and PO number, and flag mismatches over 2% for manual review.”

The BRD says the business needs faster reconciliation. The SRS says exactly what the software does to deliver it. On small projects, one document can carry both — a business-goals section up top, detailed requirements below. On anything with real budget or multiple stakeholders, keep them separate. The BRD gets sign-off from leadership; the SRS gets sign-off from whoever owns delivery.

If you only write one, write the SRS. But steal a page from the BRD and put your business goals at the top. Requirements without a “why” are impossible to prioritize when the budget gets tight — and it always gets tight.

The template: section by section

Here’s the structure we use. Copy it, delete what doesn’t apply, and fill in the rest. It maps cleanly onto how a dev shop reads and prices work.

• 1. Overview and goals — Two or three paragraphs. What is this, who’s it for, what problem does it solve, what does success look like in plain business terms. If you can’t explain the goal in four sentences, you’re not ready to spec the features yet.

• 2. Users and roles — List every type of person who touches the system. Admin, standard user, manager, external customer, API consumer. For each, note what they can see and do. Roles drive permissions, and permissions drive a surprising amount of the build cost.

• 3. Functional requirements (as user stories) — The core. What the software does, written as user stories: “As a [role], I want to [action], so that [outcome].” Group them by feature area. Number them so you can reference them later.

• 4. Non-functional requirements — How the system performs, not what it does. Speed, uptime, concurrent users, security standards, accessibility, browser support, data retention. The requirements people forget until they’re the reason the launch slips.

• 5. Integrations — Every external system you connect to. Payment gateway, CRM, email service, accounting software, SSO provider. Name the actual tools and note whether it’s read, write, or both.

• 6. Data — What data you store, roughly how it’s structured, where it lives, and any rules around it (retention, residency, PII handling). You don’t need a full schema — you need enough that an architect can sketch one.

• 7. Out of scope — Explicitly list what you are not building in this phase. This single section prevents more scope creep than any other. Write it down and it stops being an argument.

• 8. Success metrics — How you’ll know it worked. “Reconciliation time drops from 15 hours to under 2 hours per week.” Concrete, measurable, tied back to your goals.

• 9. Constraints and assumptions — Budget ceilings, hard deadlines, tech stack you’re locked into, team size, anything you’re assuming to be true. If an assumption turns out false, it becomes a change — so write them down where everyone can see them.

That’s it. Nine sections. A tight SRS for an MVP might run four pages; a complex platform might run forty. The structure holds either way.

Functional requirements: user stories that actually work

This is where most documents fall apart, so let’s do real examples.

Vague (bad): > The system should let users manage their orders.

“Manage” means nothing. Does that include editing? Cancelling? Refunds? Partial refunds? A developer reading this either guesses or pads the estimate to cover every interpretation. Both cost you.

Precise (good): > - As a customer, I want to view all my past orders in a single list sorted by date, so I can find a previous purchase quickly. > - As a customer, I want to cancel an order within 30 minutes of placing it, so I can fix a mistake without contacting support. > - As a customer, I want to request a refund on a delivered order, so I can return a faulty item — refund approval is manual by an admin (see role R2).

See the difference. Each story is one action, one outcome, testable. You can look at the finished software and say “yes, that works” or “no, it doesn’t.” Vague stories can’t be tested, which means they can’t be signed off, which means they drag on.

A good rule: if a requirement can’t be turned into a pass/fail test, it’s not finished. Rewrite it until it can.

Non-functional requirements: the ones that bite

Functional requirements get all the attention because they’re the visible features. Non-functional requirements are what make the software actually usable in production — and skipping them is how a demo that worked great falls over the day 500 real users show up.

Be specific here too. “Fast” is not a requirement. “Pages load in under 2 seconds on a 4G connection” is. “Secure” is not a requirement. “All data encrypted in transit and at rest; passwords hashed with bcrypt; role-based access control” is.

The categories worth covering: performance (response times, concurrent users), availability (uptime target), security (auth, encryption, compliance like GDPR or India’s DPDP Act), scalability (expected growth), and compatibility (which browsers, devices, screen sizes). You won’t need every category for every project. You’ll need most of them for anything customer-facing.

These requirements shape architecture. A system built for 50 users looks nothing like one built for 50,000 — and if the spec doesn’t say which you need, the system design decisions get made by default, usually the cheap way, usually wrong for where you’re headed.

The mistakes that inflate your quote

We’ve priced a lot of projects from a lot of documents. The patterns that blow up estimates are consistent.

Ambiguity. Every vague requirement forces the vendor to assume the expensive interpretation, because underestimating is how they lose money. Vague specs don’t get you a lower price — they get you a higher one with more padding.

Missing edge cases. The happy path is easy. What happens when a payment fails halfway? When two users edit the same record? When the integration times out? If the spec is silent, either the vendor guesses (and you get behavior you didn’t want) or asks mid-build (and you lose a week per question). This is one of the reasons software projects fail more often than any technical problem.

No out-of-scope section. Without a written boundary, every good idea that surfaces during the build feels in-scope. It isn’t. But the argument costs you either way.

Confusing wants with needs. Not every requirement is equal. Mark them — must-have, should-have, nice-to-have. When the budget gets tight (it will), you’ll know exactly what to cut without another round of meetings. This is also the fastest way to scope down toward an MVP that ships instead of a wishlist that stalls.

Over-specifying the how. The flip side. Don’t dictate the database, the framework, or the exact UI pixel layout unless you have a real constraint. Tell the team what and why; let the engineers own how. Over-specification either ties good hands or gets ignored — neither helps.

How LaxenTech helps

Most teams that come to us have a rough idea and a half-written doc. We turn that into a real specification — one that we, or any competent shop, can quote and build from without guessing.

Our custom software development engagements usually start with a requirements workshop: we sit with your team, pull the fuzzy goals into concrete user stories, surface the edge cases you haven’t thought about, and draw the scope line before a single line of code gets written. If you’re integrating with existing systems — ERP, payments, third-party APIs — that mapping happens here too, because integrations are where estimates most often go sideways.

You leave with a document you own. Use it to build with us, or take it to another vendor and get comparable, defensible quotes. A good spec makes you a better buyer either way — and if you’re still choosing a partner, our guide on how to choose a software development company covers what to look for.

Frequently asked questions

How long should a software requirements document be?

As long as it needs to be, and no longer. An MVP spec might run four to six pages; a complex enterprise platform can hit thirty or forty. Length isn’t the goal — clarity is. If a section adds no clarity for the people building or pricing the work, cut it. A tight ten-page doc beats a padded fifty-page one every time.

What’s the difference between a BRD and an SRS?

A BRD (Business Requirements Document) explains why you’re building something — the business case, goals, and ROI, aimed at executives. An SRS (Software Requirements Specification) explains what the software does and how it behaves, aimed at the people building it. On small projects one document can cover both; on larger ones, keep them separate so each gets the right sign-off.

Do I need a requirements document before getting a quote?

You’ll get a far better quote with one. Without a spec, vendors estimate against the most expensive interpretation of every vague point, so the number comes back high and wide. A clear requirements document lets a shop quote tightly and lets you compare vendors on equal terms. It’s the single highest-leverage document you can prepare before spending money.

How do I write functional requirements?

Use user stories: “As a [role], I want to [action], so that [outcome].” Keep each story to one action with one testable outcome. If you can’t turn a requirement into a pass/fail test, it’s too vague — rewrite it until you can. Group stories by feature area and number them so you can reference them during the build and sign-off.

What are non-functional requirements?

They describe how the system performs rather than what it does: speed, uptime, concurrent users, security standards, scalability, and browser or device support. Be specific — “loads in under 2 seconds on 4G” instead of “fast.” These requirements shape the underlying architecture, and skipping them is a common reason software that demos well falls over in production.

What should go in the out-of-scope section?

Everything you are deliberately not building in this phase — features that came up, sound reasonable, but belong to a later version. Writing them down converts every “can we also add…” from an argument into a documented change request. This one section prevents more scope creep and budget overrun than any other part of the document, so don’t leave it blank.

A good software requirements document isn’t paperwork — it’s the cheapest insurance you’ll buy on the whole project. It aligns your team, boxes in scope, and turns a fuzzy idea into something a vendor can price and build without guessing.

Start with the template above. Write your goals, list your users, turn features into testable user stories, nail down the non-functional requirements, and — above all — write down what’s out of scope. If you’d rather have engineers help you turn a rough brief into a spec you can build from, talk to our team. Bring what you have; we’ll make it buildable.