Chapter 3. Preparing to build safely — narrowing the keys you hand over

Key points

• Give the AI the key to the working folder only, never the key to the whole house
• Do not put files of unknown origin into the working folder
• Write a rule book once, and you stop repeating the same instructions

A folder decides how far the AI can reach

Chapter 2 of the previous part set out the security principles: anonymise, turn training off, keep it local. Nothing about that changes for coding. If anything, because the AI is actually operating files, one more notch of caution is needed.

When you use an AI development tool, the first thing you always do is say "work in this folder". That gives the AI access to only the files inside that folder.

Picture handing over the key to one room. Give it the key to the study, and the AI works within the study. Hand over the master key to the whole house, and it can walk into the bedroom, the kitchen, the storeroom.

The same holds on a computer. Nominate your entire user folder as the workspace and your desktop, documents and photographs all fall within the AI's reach. The AI has no malice, but it can misread an instruction. "Tidy up the unnecessary files" being read as "delete the files in this folder", and important documents disappearing, is a genuinely possible accident.

Which is why:

Make a folder for the work, and hand the AI the key to that folder only.

That is the most basic rule there is. Think of it as the practical form of "tidy the desk" and "keep it local" from the previous part.

How to set up a working folder

1. Decide a parent folder. Not directly in your user folder, but one level down, make a dedicated folder. A name such as code or ai-projects — English, so that later you can see at a glance that it is where AI work lives.

2. One thing you are building = one folder. A single thing you are building is called, in the development world, a project. A profile site is one project; a full website is another. Hold to one project, one folder and management stays intact, and the AI's reach stays minimal.

3. Rules for folder names. Some tools throw errors on folder names in Japanese or with unusual characters, so standardise safely from the start.

• half-width alphanumerics, - and _ only
• no spaces
• no non-Latin characters
• a date at the front makes chronology obvious (e.g. 20260529_self_introduction)

Do not put unfamiliar files into the working folder

Equally important: do not put files of unknown origin into the working folder.

There are plenty of useful-looking templates and samples online, and some of them carry hidden instructions aimed at the AI. This technique is called prompt injection. A file that looks perfectly ordinary can contain instructions the AI reads and executes.

The instinct from the previous part — that anything you hand an AI can become an instruction to it — applies here too. Put only material of trustworthy origin into the working folder. That alone reduces the risk considerably.

Write a rule book for the AI

AI tools have a trait: change conversation and the earlier rules are forgotten. So you end up appending "answer in English", "check with me before big changes" every single time.

The useful mechanism here is a rule book the AI reads first. Put a file of rules in the expected place and the AI reads it before starting work each time. The filename differs by tool.

Write your own preferences — the ones that hold across every project.

• Reply in English throughout.
• Explain so a beginner can follow; unpack any jargon.
• Always check with me before large changes or deleting files.

There is no need to write perfect rules from the start. When you notice "I say this every time", add it. Exactly as the previous part described growing an Obsidian knowledge base, a rule book is something you grow as you use it.

Chapter 3 summary

• Hand over the key to the working folder only; hold to one project, one folder
• Keep files of unknown origin out of the working folder (against prompt injection)
• Write a rule book once and instructing gets easier; grow it as you go