GUIDES
3 Ways To Build An AI Second Brain 📚
Ranked easiest to most powerful, with the real setup for all three. Including the one I actually use to run two businesses.
People make a second brain sound complicated. It is not.
A second brain is one place where all your important information lives: your files, documents, projects, and notes. It matters because of what happens when you point AI at it. Instead of re-explaining your job and your goals in every chat, the AI already knows where everything is and can reach all of it.
There are three ways to build one, ranked easiest first. Pick one. You can switch later, because all three are just files.
All Three, Side By Side
The whole decision on one screen. Pick your row, then jump to that section.
| Method | Best for | Setup | Pro | Con |
|---|---|---|---|---|
| 3. Claude Projects | Beginners, and anyone who wants this working today | 15 min | Zero technical skill, works right away | Lives inside Claude, pulls only what it judges relevant |
| 2. Obsidian | Note takers who want an app and want to own their notes | An hour, plus a week to settle in | Free for personal use, files stay on your computer | Real learning curve, easy to organize instead of use |
| 1. A folder of files | Anyone ready to use Claude Code or Codex | 30 min | Most flexible, any AI can read it, no lock-in | No pretty interface, strange for about a day |
None of these is a weekend project. The hard part was never the building.
Claude Projects, The Easiest
Start here if you have never done this. You make a Project inside Claude, drop your files in, write a short set of instructions, and every chat inside it already knows who you are.
In Claude, open the sidebar, click Projects, then New project. Name it after what it is for: My Business, Client Work, Job Search. "Second Brain" is a bad name, because it tells you nothing about what belongs in it. Make one project per big area of your life, not one giant project for everything.
Click Add content and upload into the project knowledge, in this order:
Do not upload your whole hard drive. The knowledge box is generous, but not infinite.
Almost everyone skips this, and it is what makes the project feel smart. Write four things in the instructions box:
A stale second brain is worse than none, because you trust it and it is wrong. Two habits: at the end of a good chat, have it write a short summary file of what you decided and upload that back in. Once a month, delete anything out of date and re-upload what changed. Ten minutes, on your calendar, or it will not happen.
Obsidian
This is the one the internet is obsessed with. I think it is overhyped, but it is genuinely good. Your notes live as plain markdown files on your own computer, it is free for personal use, and you can point AI at the folder.
Download Obsidian from obsidian.md. On first open it asks you to create a vault, which is just a folder on your computer. Put it somewhere you will find it, like Documents. If you use iCloud, Dropbox, or Google Drive, put the vault inside that synced folder so it backs up for free. Make one vault, not three, because the AI sees one folder at a time.
Four folders is enough for years:
No tags or naming conventions yet. Write notes for two weeks, then let the structure follow what you actually have.
Your vault is a normal folder of markdown files, so you have three options:
A Folder Of Files, What I Use
This is the setup I actually run my businesses on. No app, just a folder on my desktop with hundreds of plain files that Claude Code or Codex reads across, adds to, and pulls from in seconds. It sounds too simple to be the most powerful option, and that is exactly why it is: nothing sits between your information and the AI. No app deciding what it can see, no company owning the format, no lock-in.
Right-click your desktop and make a new folder. Call it brain. Inside it, make three folders: about-me, projects, and reference. Add more later if you need them, not now.
In about-me, make a file called context.md. Every AI you point at this folder reads it first. Write six things in plain sentences:
Fastest way: turn on voice dictation, talk for two minutes about all six, and tell the AI to clean it into a markdown file. Talking beats staring at an empty page.
Every file is a .md file, which is just a text file. Name files so you know what is inside without opening them: brand-voice.md, 2026-goals.md, client-acme-notes.md. Not notes2.md or final-final.md. Lowercase with dashes, one file per topic.
Start Claude Code or Codex in that folder, then ask something you would normally have to explain first, like based on everything in this folder, what should I focus on this week? It goes both ways too: end good sessions with save what we decided as a new file in projects, and the second brain grows while you use it.
Which One Should You Pick
All three fail for the same reason, and it is never the tool. It is people building the system and never filling it. Go write your file about yourself right now. One file, ten minutes. Nothing else on this page works without it.
In outbound marketing and career positioning, generic applications have near-zero conversion. Treat yourself as a high-ticket solution: identify the company's pressing operational pain points, build a mini-audit or work sample using AI before you apply, and bypass crowded channels by reaching out directly to the decision-maker with structured value.