Sep 20, 2026 · Free Guide

“BRAIN” Build Your AI Second Brain in 15 Minutes (It's Just a Folder)

Your AI forgets you every time you open a new chat. The fix isn't a database or a $50 a month app. It's a folder on your computer that your AI reads before it answers. One prompt builds it, and you own it forever.

Forget the flashy visuals. Here's what a second brain is.

Those glowing knowledge graphs you see online are there because they look good on video. They aren't what makes a second brain work.

A second brain does two jobs. It gives your AI access to the files you choose. And it makes the right file easy to find at the right moment.

So it's a filing cabinet, and that's good news. A filing cabinet doesn't break, doesn't need updates, and doesn't lock you into one company.

HOW IT WORKS

The four files that do all the work

FileWhat it does
me.mdEverything about you. Your business, your offers, your customers, how you talk.
INDEX.mdThe table of contents. One line for every file in the brain. Your AI reads this first, so it knows where everything is.
recent.mdA running diary. A short summary of each conversation, with the date.
The rules noteLives in your CLAUDE.md file (or AGENTS.md if you use Codex). It tells your AI: check the table of contents before answering, and file anything new.

The rules note is what makes this work. Your AI doesn't get any smarter. It gets a habit of checking the cabinet before it answers.

STEP 1

Paste the prompt

Open the tool you already use: Claude Code, Claude Cowork, or Codex. Paste the prompt below.

It does not start by quizzing you. It first gathers what your AI already knows about you. That includes your instruction files, your memory, your project folder, and your recent sessions. It fills in your profile by itself and shows you the draft.

You only answer what's missing, which is five questions at most.

The brain prompt
Build me a second brain using only folders and plain text files.

STEP 1: GATHER WHAT YOU ALREADY KNOW ABOUT ME
Before asking me anything, collect everything you can already access about me and my business:
- Any memory you have of me and any instruction files (CLAUDE.md, AGENTS.md, memory folders, custom instructions)
- The files in the folder we are working in right now
- Summaries of my recent past sessions with you, if you can read them. Skim the last 30 days. Do not read everything.
Do not invent anything. If you are unsure about something, mark it as unsure.

STEP 2: FILL IN THE PROFILE YOURSELF
Answer these from what you gathered: who I am, what my business does, my offers and prices, who my customers are, my goals this year, the tools I use, key people I work with, how I like to talk and write, and decisions or preferences I have told you before.
Show me the draft in plain English. Then ask me ONLY about what is missing or marked unsure, one question at a time, 5 questions max. If you know almost nothing about me, interview me with about 10 questions instead. If I paste a profile from another AI tool, use that too.

STEP 3: BUILD THE BRAIN
Create a folder called "brain" in my home folder with subfolders: people, projects, decisions, chats, inbox. Then create:
- me.md: the confirmed profile
- INDEX.md: a table of contents listing every file in the brain with a one-line description. Keep it updated forever.
- recent.md: a running log. Add a dated 3-line summary at the end of every conversation.
- CLAUDE.md with these rules, plus an identical copy called AGENTS.md:
  - Read INDEX.md and me.md before answering anything about me or my business.
  - When I tell you something worth keeping (a decision, preference, person, project), or when I say "save this" or "remember this", save it as its own small file in the right folder and add it to INDEX.md. Do not ask first.
  - Update existing files instead of creating duplicates. Remove facts that turn out to be wrong.
  - Always use real dates, never "last week".
  - Never store passwords, API keys, or financial account details in the brain.
  - When I say "clean up my brain": go through recent.md and the inbox folder and file anything worth keeping from the past week that was not filed yet, merge duplicates, move recent.md entries older than 14 days into the chats folder, re-scan my work folders for new or changed files, and fix INDEX.md.

STEP 4: MAP MY WORK
Ask me which folders hold the work I want you to know about (SOPs, client folders, projects). Show me the list of what you plan to scan before scanning. Do NOT copy files into the brain. For each project or client, write one summary page in brain/projects: what it is, where it lives on my computer, the key files, and current status. Add pointers to INDEX.md.
Never open or store passwords, API keys, .env files, or tax and banking documents. Skip them and tell me what you skipped. Skip images, videos, code libraries, and downloads.

STEP 5: MAKE IT PERMANENT
Add a short note at the top of my global instructions file so every future conversation uses the brain. For Claude that is ~/.claude/CLAUDE.md. For Codex that is ~/.codex/AGENTS.md. If both tools are installed, do both. The note should say: my brain lives at ~/brain, read ~/brain/INDEX.md and ~/brain/me.md first, and follow the rules in ~/brain/CLAUDE.md. Do not delete anything already in those files.

STEP 6: WEEKLY CLEANUP
Set up a weekly scheduled task for Sunday night that runs "clean up my brain". If you cannot schedule tasks in this app, tell me plainly and remind me to say "clean up my brain" once a week.

STEP 7: PROVE IT WORKS
Tell me in plain English what you built. Then tell me three things you know about me and one thing you know about my projects, and which file each came from.
STEP 2

Tell it where your business lives

This is Step 4 inside the prompt. Your AI asks which folders hold your work.

Point it at your SOPs, your client folders, your projects, and anything else you want it to know about.

It shows you the list before it scans anything. You approve the list, and then it goes.

STEP 3

It builds the map

Most people copy everything into their second brain. That gives them two versions of every file, and both go stale.

Yours doesn't copy anything. It writes one summary page per project or client: what it is, where it lives on your computer, the key files, and the current status. Your files stay exactly where they are. Your AI now knows they exist and where to find them.

The three phrases you'll use

Say thisWhat happens
“Save this” or “remember this”Files what you said, right now, in the right folder.
“Clean up my brain”Merges duplicates, files anything it missed this week, archives old entries, and re-scans your folders for new work.

You don't need to learn any commands beyond these.

The Sunday night cleanup

The prompt sets up a weekly task that runs “clean up my brain” every Sunday night.

Two things to know. It only works in apps that can schedule tasks. And your computer has to be on with the app open.

If the app can't schedule, it will tell you. If you miss a week, say “clean up my brain” yourself and it catches up.

READ THIS

The rules that keep you safe

Your AI reads this folder every conversation, so treat what goes in it accordingly.

  • No passwords and no API keys, ever.
  • No banking or tax documents.
  • The prompt already tells your AI to skip all of these and report what it skipped. Read that report.
  • If you point it at client folders, remember that the client info ends up in summaries. Keep the brain folder private.

Quick answers

My history is in the ChatGPT app, not Claude Code or Codex. Paste this into ChatGPT, copy the answer, and paste it in when the brain prompt shows you its draft. It will use it.

Ask ChatGPT this first
Write out everything you know about me as a detailed profile: who I am, my business, my offers, my customers, my goals, my preferences, and how I talk. Be specific. Don't invent anything.

How do I back it up?Put the brain folder inside iCloud Drive, Google Drive, or Dropbox. That's all it takes.

Can I read the files myself? Yes. They are plain text, so you can open any of them and fix anything.

Does it work with more than one AI? Yes. The prompt creates both CLAUDE.md and AGENTS.md, so Claude and Codex read the same brain.

All Resources

Claude Code and CoworkDownload the Claude desktop app
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CodexOpenAI's coding agent
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Garry Tan's gbrainThe heavy duty version, if you outgrow the folder
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The original reelWatch the 3 steps
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The Next Step

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