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undefined-ui/second-brain-os

A starter vault, guide, skills and scripts for an AI agent that builds and maintains a linked markdown knowledge base in Claude Code and Obsidian.

Open-source alternative to:Notion

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What is it?

Second Brain OS is a toolkit for building a personal knowledge base that an AI agent files, links and maintains for you. Sources such as web articles, transcripts, PDFs and chat exports go into a raw folder, and the agent turns them into linked wiki pages stored as plain markdown on your own machine. The repo is designed to work with Claude Code, and Obsidian is used as a viewer rather than a requirement.

The repository bundles a starter vault with a CLAUDE.md contract and page templates, 18 skills covering ingest, lint, merge, query and review, 6 subagents, 72 slash commands, and four dependency-free Python scripts for link checking, vault statistics and graph export. A Claude Code plugin packages the course's practice tasks, such as context audits and eval bootstrapping.

Beyond the toolkit, the repo includes a guide to the approach, a seven-module course on building agents, and handbooks on knowledge graphs, harnesses, loops and evals, with a curated list of related papers and tools.

Key features

  • 01Ingests raw sources into linked, one-idea-per-page wiki articles
  • 02Ships 18 skills and 72 slash commands for ingest, lint, merge, query and review
  • 03Includes a starter vault with a CLAUDE.md contract and four page templates
  • 04Provides dependency-free Python scripts for broken links, vault stats and graph export
  • 05Packages course practice tasks as a Claude Code plugin

Use cases

  • Building a personal knowledge base from saved articles, videos and PDFs without manual filing
  • Keeping an Obsidian vault linked and deduplicated with scheduled agent runs
  • Learning how to design agent skills, loops and evals through the included course

Quick start

  1. 1

    Clone the repository

    git clone https://github.com/undefined-ui/second-brain-os.git
  2. 2

    Copy the starter vault to ~/brain

    cp -r second-brain-os/vault-template ~/brain
  3. 3

    Copy the skills, commands, agents and scripts into the vault, then remove the folder READMEs

  4. 4

    Open the vault and start Claude Code

    cd ~/brain && claude

Things to know

  • The workflow is built for Claude Code, and the README expects you to work through nine setup guide pages before it runs well.

In collections

Claude Code tools, skills & pluginsOpen-source AI agent frameworks & appsAI agent skill librariesStatic site generators & documentation tools

Topics

#ai-agents#claude-code#knowledge-management#obsidian#personal-knowledge-base#knowledge-graph#markdown#agent-skills#claude#claude-skills

FAQ

What is second-brain-os?
A starter vault, guide, skills and scripts for an AI agent that builds and maintains a linked markdown knowledge base in Claude Code and Obsidian. Second Brain OS is a toolkit for building a personal knowledge base that an AI agent files, links and maintains for you. Sources such as web articles, transcripts, PDFs and chat exports go into a raw folder, and the agent turns them into linked wiki pages stored as plain markdown on your own machine. The repo is designed to work with Claude Code, and Obsidian is used as a viewer rather than a requirement.
Is second-brain-os free to use? What license does it have?
second-brain-os is open source under the MIT license. Check the license terms before using it in commercial products.
Is second-brain-os still maintained?
Actively maintained. The last commit to second-brain-os was on Nov 3, 2026.
What can I use second-brain-os for?
Building a personal knowledge base from saved articles, videos and PDFs without manual filing Keeping an Obsidian vault linked and deduplicated with scheduled agent runs Learning how to design agent skills, loops and evals through the included course
How do I install second-brain-os?
Clone the repository: git clone https://github.com/undefined-ui/second-brain-os.git Copy the starter vault to ~/brain: cp -r second-brain-os/vault-template ~/brain Copy the skills, commands, agents and scripts into the vault, then remove the folder READMEs Open the vault and start Claude Code: cd ~/brain && claude
Where can I get second-brain-os?
The source code and installation instructions are on GitHub: https://github.com/undefined-ui/second-brain-os

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