← The stack
FROM THE BOOK · STEP FOUR: BUILD TOOLS THAT TAKE ACTION

PRD Builder

Telling an AI "build me a customer portal" is like telling a builder "build me a house" and then leaving the country. You'll come back to a house. It won't be your house.

You're not meant to hand-write this from a blank page. Voice-note the brief, let the AI draft it, then use this to make sure every section exists. Your job is the context and the judgement; the drafting is the machine's.

Runs in your browser · what you type stays on your machine

PRD completeness

0%

The tool's name

Working title is fine.

What it's for

The problem, in a sentence, stated so a stranger would understand it. Who does it now, where it hurts, in hours or pounds.

Who uses it

You? Your staff? Your customers? This changes everything about how it's built.

What it must do

The actual features, listed. Not vague wishes, concrete jobs.

What it must NEVER do

Just as important. 'It must never go live with a product before a human has approved it.'

What 'done' looks like

The measurable thing. Include the number: the annual run cost has to land below the old thing, by a margin you write down.

The rules and the edge cases

The exceptions. The things that go wrong every third Tuesday that only you know about.

The stack

What it leans on: somewhere to store data, something people see, payments if money moves. Not sure? Use the stack prompt below.

Most of it rules, a sliver of judgement

Most of what a good tool does should be plain, fixed rules the machine runs the same way every time. The AI only does the genuinely fuzzy bit. Every fixed thing you let the model "decide" is a thing it can get confidently wrong, and a cost you pay on every run.

Then make the AI earn its keep before anything is built

The stress-test prompt

Here's my PRD for a tool I want to build. Before we build anything:
What have I missed? What questions would a good engineer ask me? What could go wrong?
What would a competitor's version do that mine doesn't? What edge cases catch people out on jobs like this?
What does a proper version include that a naive one forgets?

---

# PRD: Untitled tool

## What it's for

_To be filled in._

## Who uses it

_To be filled in._

## What it must do

_To be filled in._

## What it must NEVER do

_To be filled in._

## What "done" looks like

_To be filled in._

## The rules and the edge cases

_To be filled in._

## The stack

_To be filled in._

Not sure about the stack? Ask for the cheapest, simplest one

Based on this PRD, suggest the cheapest, simplest stack that does the job properly.
For each moving part (somewhere to store data, something people see, payments if any), name the category first, then one example, and say roughly what it costs to run monthly.
I keep the judgement on the trade-offs; you make the recommendation and justify it.

---

# PRD: Untitled tool

## What it's for

_To be filled in._

## Who uses it

_To be filled in._

## What it must do

_To be filled in._

## What it must NEVER do

_To be filled in._

## What "done" looks like

_To be filled in._

## The rules and the edge cases

_To be filled in._

## The stack

_To be filled in._