An AI second brain that is just simple notes

An AI second brain sounds like a big project. A system of linked notes, tags, dashboards, and an assistant wired into all of it. It does not have to be. The version most people keep using is much smaller: plain notes you actually write, and an agent that can read and write them for you.

What a second brain is

The idea is old and simple. Your head is good at thinking and bad at storing. So you keep what you want to remember somewhere outside it: ideas, plans, lists, decisions, things you learned. Then you can let go of them without losing them.

A notebook is a second brain. So is a folder of documents, or a notes app on your phone. The name makes it sound new. The habit is not.

Why most setups get heavy

Somewhere along the way the second brain turned into a hobby. People build folder trees, tagging rules, templates for every kind of note, links between everything, weekly processing rituals. It is satisfying for a month. Then capturing a thought takes a decision about where it goes, and the notes stop coming.

Adding AI on top often makes it heavier still. Now there are embeddings to set up, integrations to maintain, and a chat window that summarises notes nobody wrote. The system gets smarter while the notes get fewer.

The fix is not a better structure. It is less of it.

The light version: notes plus an agent

Here is an AI second brain you can set up in an afternoon and keep for years.

1. A simple notes app. One list of notes. No folders to decide on. Search to find things again. A star for what matters now, archive for what is finished.
2. An agent connected to it. An assistant such as Claude that can read your notes, write new ones and update the ones you have.
3. A few habits. One topic per note, plain titles, and asking the agent to update rather than duplicate.

The agent does the parts that used to make a second brain heavy. It turns a rambling list of thoughts into a tidy checklist. It finds the note about the boiler when you cannot remember what you called it. It adds today's decision to the right note instead of starting a new one. You keep doing the part only you can do: noticing what is worth keeping.

What to capture

• Lists you return to. Shopping, packing, books, gifts, things to fix.
• Plans in progress. Training, a trip, a renovation, a course you are taking.
• Decisions and their reasons. What you chose and why, so you do not decide it again next year.
• Things you learned. A recipe adjustment that worked, how you fixed the printer, what the doctor recommended.
• Ideas, briefly. One line is fine. You can ask the agent to expand it later.

What to skip: copies of things that already live somewhere else, and anything you would not want an assistant to read. A second brain does not need to hold everything. It needs to hold what you use.

How to ask

Once your notes are connected, the whole interface is plain language. A few patterns cover most of it:

• Capture. "Save this as a note called Boiler service, with the date and what the technician said."
• Recall. "What did I decide about the kitchen tiles?"
• Update. "Add these two books to my reading list note."
• Tidy. "Turn my trip ideas note into a checklist with sections."
• Review. "Look at my starred notes and tell me what is still open."

If you use Claude, connecting your notes takes a minute and works on the web, on desktop and on your phone. The steps are in Claude connectors for your notes.

Start with three notes

Do not import your whole life on day one. Start with three notes you will open this week. A shopping list. A plan you are in the middle of, such as a trip or a training block. And one note called Decisions, where anything you settle gets a line and a date. Use them for two weeks, with the agent doing the tidying. Add a note only when you catch yourself wishing it existed. That is how the system stays light enough to keep.

Keep it yours

A second brain is personal, so where it lives matters. Pick a place where you can see which assistants are connected and cut one off at once. Pick a place that does not use your notes to train AI models. And pick one where a lapsed subscription never locks you out of reading your own notes.

Then keep it small. When the AI second brain starts to feel like a project, remove something. The notes are the point. The agent is just the help.

Very Simple Notes is a simple notes app built to be that light second brain: notes and checklists without visible markup, search, star and archive, and a connector so your agent can read and write them. Hosted in the EU, no ads. The app is on iPhone today. It costs $0.99 a month, and the first month is free.