A second brain is a folder your AI keeps for you. Notes on your business, your clients and how you work, which the AI writes, updates and reads before every task, so you stop explaining yourself in every new chat. The pattern is Andrej Karpathy’s: you feed it, and “the LLM writes and maintains all of it.”
Source: LLM Wiki, Andrej Karpathy, April 2026.
What’s in the folder
| File | What it holds |
|---|---|
| raw/ | Everything you give it, exactly as it came. Never edited |
| me.md | Your business, offers, customers and goals |
| people.md | Your clients and contacts, and what’s open with each |
| voice.md | How you write, so its drafts sound like you |
| rules.md | Every correction you’ve made, one line each |
| INDEX.md | One line per file. It reads this first |
Plain text you can open and fix. Fast-changing facts, like a price or a balance, it checks at the source.
📋 Paste this into your AI
Copy this into Claude or ChatGPT, fill in the two brackets, and paste a few emails you’ve sent under it.
You’re my second brain. I run [your business — what you sell, and to whom]. Most of my week goes on [the work that fills it — e.g. quoting jobs, chasing invoices].
Build the first version now, from that and anything I paste below:
- me.md: my business, offers, customers and goals for the next 90 days.
- people.md: each client or contact I mention, and what’s open between us.
- voice.md: how I write, as 10 short rules, each with a real line of mine if I pasted any.
- rules.md: read INDEX.md first and rules.md before every task; save what I give you to raw/ unchanged; when I correct you, add the fix here as one line; never send, delete or buy without my yes.
- INDEX.md: one line per file.
Save them as files in a folder called brain if you can; if not, show each one in full. Then ask me the five questions that would make this brain most useful.
What comes back is your brain’s first five files, built around your business.
Where to keep it
| Where | How | What you get |
|---|---|---|
| Claude desktop app | Give it a folder called Brain (paid plans) | It writes and updates the files itself |
| Grok Bot | A bot called Brain, with Gmail and Google Calendar connected (paid plans) | It runs in the cloud, so it keeps filing with your laptop shut |
| ChatGPT or Claude, free | A project called Brain | The project holds the files; you add its updates |
The three traps
- Chat memory isn’t a brain. It keeps short summaries the AI picks. A file keeps exactly what you wrote, and any AI can read it.
- Unfed, it goes stale. Once a week, have it read the whole folder and flag contradictions and old facts. Karpathy calls it a lint pass.
- It drafts, you send. Anything that sends, deletes or pays waits for your yes.
Start this week
- Pick its home. A Claude folder, a Grok Bot or a free project.
- Paste the prompt. With a few sent emails under it. Save the five files.
- Feed it daily. Drop in what’s worth keeping. Correct it once, and the fix lives in rules.md.