Full Guide: Build An AI Second Brain With Codex

TL;DR

Build a personal AI knowledge system in Obsidian and Codex combining a wiki, journal, and CRM that retrieves your saved content to answer questions.

Key Points

• 1.The system has three core pillars. A wiki/knowledge base for saved web content, a CRM for contact notes, and a journal that pulls from both to give grounded, personalized responses instead of generic AI answers.
• 2.Andrej Karpathy's LLM wiki architecture is the foundation. The creator explicitly credits Karpathy's GitHub design, using Obsidian as the markdown front-end and extending it with journal and CRM layers on top.
• 3.Two free tools are all you need. Obsidian (obsidian.md) serves as the markdown organizer and visibility layer, while Codex acts as the AI coding and chat interface — both are free to start.
• 4.The Obsidian Web Clipper automatically ingests YouTube transcripts and articles. Install it as a Chrome extension, configure it to save to the RAW folder in your vault, and it pulls full video transcripts with one click.
• 5.Codex processes raw files into an interconnected wiki with entities, concepts, and cross-links. It extracts people, tools, companies, and ideas, auto-links related notes, moves processed files to a /processed subfolder, and updates index.md and log.md.
• 6.The journal feature grounds AI responses in your personal saved knowledge. Prefix a Codex chat with 'journal,' and it queries the wiki, past journal entries, and CRM before responding — surfacing relevant content you previously saved rather than giving generic advice.
• 7.The CRM stores and retrieves contact details conversationally. Tell Codex 'add to CRM' with a person's name and details; it creates a named markdown file, updates a CRM index alphabetically, and lets you query contacts later (e.g., 'Where did I meet Matthew Berman?').
• 8.A Codex automation runs every hour to process new files and back up to GitHub. Set up an hourly automation in Codex targeting the RAW folder, and add a private GitHub repo commit step so the entire vault is versioned and backed up automatically.