PRD vs MRD vs BRD vs SRD: Which Doc Do You Actually Need?

PRD, MRD, BRD, SRD, RFC. Five acronyms, heavy overlap, and a genuine question underneath: which of these do you actually have to write?

The short answer for most software teams is one document, usually the PRD. The longer answer is that each of these formats exists to answer a different question, and knowing which question you are stuck on tells you which document — if any — will help.

The one-line version

Document	The question it answers	Usually written by
MRD — market requirements	Is there a market worth serving here?	Product marketing / product
BRD — business requirements	What does the business need, and why fund it?	Business analyst / sponsor
PRD — product requirements	What must we build, for whom, and how will we know it worked?	Product manager
SRD / SRS — software requirements	How must the system behave, precisely?	Engineering / systems analyst
RFC — request for comments	Which technical approach should we take?	Engineer

Read down that column of questions and the sequence is obvious: market → business case → product → system → implementation. Each document narrows the one above it.

Most teams do not need all five, because most teams do not have all five questions open at once.

MRD vs PRD

The MRD makes the case that an opportunity exists: who the segment is, how large it is, what they do today, what competitors offer, why the timing works. It is an argument, and its output is a decision about whether to invest.

The PRD starts after that decision. It assumes the opportunity is real and specifies the response — users, scope, requirements, success metrics, edge cases.

The distinction matters when your document is confused about which job it is doing. A PRD that spends three pages justifying the market and half a page on requirements is an MRD wearing the wrong title, and it will get approved without anyone noticing the requirements are thin.

In practice the standalone MRD has largely disappeared from software teams. Its content survives as a product strategy doc, a one-pager, or the problem-alignment section at the top of the PRD. That consolidation is fine — as long as the argument still gets made somewhere, rather than being skipped because it no longer has a document of its own.

BRD vs PRD

The BRD states what the business requires and why it is worth funding: objectives, stakeholders, constraints, success criteria in business terms, sometimes cost and compliance obligations. It is an approval artifact.

The PRD translates that into product behaviour.

Whether you need both is mostly a question of how your organisation approves work. Enterprises with formal procurement, regulated industries, and agency-client relationships genuinely need the BRD — it is a contract-shaped document, and the PRD is not.

Everywhere else, two documents is a liability rather than rigour. Requirements written in two places drift, and the moment they disagree nobody can tell you which one is authoritative. If one team owns both the outcome and the build, fold the business case into the PRD's problem and goals sections and keep a single source of truth.

SRD vs PRD

This is the cleanest split of the five, and the most frequently violated.

A PRD says what must be true. An SRD says how the system behaves. The PRD deliberately stops before prescribing implementation, so that engineers can apply their own judgment to the how.

PRD:  A member invited to a full workspace must be told the workspace is at
      capacity, and the owner must be notified.

SRD:  POST /invites returns 409 with code SEAT_LIMIT_REACHED when
      seats_used >= seats_purchased. The handler emits workspace.seat_limit
      to the owner's notification channel within 30s.

Both are correct. They are answering different questions, and mixing them into one document is the most common structural failure in specs — a PRD that names database columns has stopped being a product requirements document and become an under-specified technical one.

Most software teams have replaced the formal SRD with a technical design doc or an RFC owned by engineering, written after the PRD settles what the product must do. That is a good trade: the same content, in the hands of the people who will implement it.

Where the RFC fits

An RFC proposes a technical approach and invites disagreement before the work starts. It is closest to the SRD in subject matter but different in posture — an SRD specifies, an RFC argues.

RFC and PRD are complements rather than alternatives. The PRD constrains what the system must do; the RFC chooses among the ways to do it. If your team writes RFCs and no PRDs, you will build well-engineered solutions to problems nobody framed. If you write PRDs and no RFCs, you will get architectural decisions made silently inside pull requests.

So which one should you write?

Work backwards from the question you cannot currently answer.

• You cannot say who this is for or why now → you have a strategy problem. Write the market argument, whether or not you call it an MRD.
• You cannot get the work funded or approved → a BRD, or a one-pager, if your organisation will accept one.
• You cannot tell engineering what "done" means → a PRD. This is the common case.
• Engineering understands the goal but disagrees on approach → an RFC or technical design doc.
• You are integrating with a system that has hard contracts → an SRD-style spec for the interface, even if the rest lives in the PRD.

For a small team shipping software, the honest answer is almost always: one PRD, done properly. A single document with a real problem statement, measurable goals, explicit in and out of scope, and testable acceptance criteria covers what the MRD, BRD and SRD would each contribute at that scale.

The failure mode worth naming

Adding documents is a popular substitute for improving one.

When specs keep going wrong, the instinct is to introduce another artifact — a BRD to catch the business case, an SRD to catch the technical gaps. It feels like process maturity. Usually it is displacement, because the underlying problem is not that the PRD lacked a sibling. It is that nobody reviewed it.

Document count is not rigour. A four-document stack that nobody pressure-tests is weaker than a single PRD someone genuinely tried to break, and it costs four times as much to maintain.

If you are deciding between writing a second document and reviewing the first one properly, review the first one.

FAQ

PRD vs MRD? MRD argues the market opportunity is real; PRD specifies the response. Most teams have folded the MRD into a strategy doc or the PRD's problem section.

Do I need a BRD and a PRD? Rarely both, unless you have a formal approval or procurement gate. Two documents means two places for requirements to drift.

SRD vs PRD? The SRD specifies system behaviour in implementation terms; the PRD stops short of prescribing how. Most software teams use a technical design doc or RFC instead.

Which should a small team write? One. A properly reviewed PRD covers what all of them would contribute at that size.