Second Brain AI — AI skill for Claude Code

🧠 A second brain that works for you: Obsidian + an AI agent

**What happens when a personal knowledge base stops being something you *read* and becomes something an AI agent *works in* every day.**


This is a write-up of a system I designed and run for a household of two: an Obsidian vault of plain Markdown files, a Claude Code agent that reads and maintains it, a handful of small scripts, scheduled tasks, and push notifications to our phones. It has been in daily use for weeks. The real vault stays private; this repository contains the method, a **starter vault with invented example data**, and the notification script with quiet hours enforced in code.

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The idea in one paragraph

Most "second brains" are archives: you put notes in, and on a good day you find them again. Here the vault is the **shared memory between a person and an AI agent**. You say, in your own words and messily, *"add the new router to the inventory"*, *"remind me tomorrow at three to call the garage"*, *"what's the tyre pressure on the car?"*. The agent decides where things go, keeps the structure consistent, answers from the documents and pushes what matters to your phone at the right moment. You never organise anything by hand, and nothing lives in an app you can't read without it.

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Architecture

          ┌──────────────────────────────────────────────┐
          │  Obsidian vault  (plain Markdown + YAML)      │
          │  synced to every phone and computer          │
          │  (Syncthing, no cloud account needed)         │
          └───────────────┬──────────────────────────────┘
                          │ reads / writes files
          ┌───────────────▼──────────────────────────────┐
          │  AI agent (Claude Code)                       │
          │  · instructions file  · vault rules           │
          │  · hand-off note      · long-term memory      │
          └──┬──────────────┬───────────────┬─────