In Part 1, we covered what Claude Code actually is and why it changes the game for sustainability professionals.

In Part 2, we walked through the setup. Web version. GitHub connected. Environment created. You are in.

Now comes the part most people rush past.

Before you build a single deliverable, before you write a single prompt inside Claude Code, you need to understand one thing: the folder.

Not in a technical sense. In a practical sense. What goes inside it, why it is structured the way it is, and what happens when you skip the setup and go straight to building.

Spoiler: you waste an afternoon and end up with bad quality output that has nothing to do with your actual work. That we must avoid.

This article is about making sure that does not happen to you.

Here is something nobody tells you clearly when they introduce Claude Code.

The terminal, the prompts, the actual moment of building, that is maybe 5% of the process. The other 95% is preparation. It is the work you do before you open Claude Code. The files you write. The context you provide. The brief you build.

Claude Code is not a magic box. You do not open it, type "build me a net zero dashboard," and walk away with a finished product.

What Claude Code actually does is take everything you give it and turn it into structured, professional output. The quality of what comes out is directly proportional to the quality of what goes in.

| Garbage in, garbage out. Still applies.

So before we talk about what to put inside your folder, let us talk about where that folder actually lives. Here we have to always distinguish between using Claude Desktop vs Claude web. I recommend you start with desktop until you are comfortable to switch if needed (not necessary)

Simple answer: on your computer. A regular folder on your hard drive, like any other.

You create it, you name it something clear, and you point Claude Code at it. Claude Code reads from that folder and writes back into it. That is the whole setup.

I name my folders after what I am building. Something like The-Corporate-NetZero or Supplier-Engagement-Tool. One folder, one project.

Now let me show you what goes inside.

Here is the folder structure I use for every sustainability project I build in Claude Code.

Let me walk you through what each part does.

CLAUDE.md 

The first file Claude reads at the start of every session. It is your onboarding document. It tells Claude who you are, what you are building, and how you want it to work.

Without it, you repeat yourself every single time you open a new session. With it, Claude already knows your context before you type a word.

Think of it as briefing a new team member before they start. You do it once. They can actually work.

CLAUDE.md is a short file. Under 100 lines. It is not a brief, not a specification, not a strategy document. It is a routing file. It tells Claude where everything is, how to behave, and what it should never do without asking you first.

We will build this together in Part 5.