← Obsidian
Matt Wolfe
Full Guide: Build An AI Second Brain With Codex
4 min read6 May 2026Worth watching
TL;DR
Matt Wolfe builds a fully functional AI second brain using Obsidian and Codex, combining a wiki knowledge base, a CRM, and a journaling system that responds using your own saved content. The result is a self-building, interconnected knowledge system that gets smarter the more you feed it.
Key points
1
The system has three pillars: a wiki/knowledge base (ingested from YouTube, articles, podcasts via Obsidian Web Clipper), a CRM (contact notes from events and meetings), and a journal that pulls from both to give grounded, personalized responses
2
Obsidian acts as the visual front-end for markdown files, while Codex (the AI IDE) acts as the processing and chat layer that reads, writes, and updates those files
3
Andre Karpathy's LLM Wiki GitHub architecture is used as the foundation, providing the raw/wiki folder structure, agents.md instruction file, index.md catalog, and log.md changelog
4
Codex Automations can be set to run hourly, automatically processing any new files saved to the raw folder and committing updates to a private GitHub repo for backup
5
The journal feature grounds AI responses in your personal wiki content, past journal entries, and CRM data rather than giving generic ChatGPT-style answers
Actionable insights
→
Install Obsidian (free), create a new vault, then configure the Obsidian Web Clipper Chrome extension to save clipped content into a folder named 'raw' inside that vault — it auto-pulls full YouTube transcripts
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Use Codex to build the wiki architecture by pointing it at Karpathy's LLM Wiki GitHub page and your Obsidian vault folder; then edit agents.md to add journal and CRM rules via natural language prompts
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Set up a Codex Automation on hourly cadence with the instruction: 'If there are any unprocessed files in the raw directory, please process them, then commit and push to GitHub' — this makes the whole system run on autopilot
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To journal, open a new Codex chat in your second brain project and start the message with 'journal' — it will query your wiki and past entries before responding, making advice specific to what you have saved
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To add a CRM contact, tell Codex 'add to CRM' followed by the person's name and any details you remember — it creates a markdown file and alphabetical index entry automatically
Notable quotes
“Problem is, that's kind of where the information just goes to die. Unless you're like actively going back through and reviewing the notes all the time and searching through your second brain.”
“It's going to respond with something like, I see you're struggling with ideas for videos. Well, you saved this video 3 days ago that says you should do this, this, and this.”
“This is all just prompts at the end of the day. You just change how it gets prompted.”
Worth watching?
✅
Worth watching the full video?
Watch if you want to see the actual build process live — the key steps and prompts are all captured here, but the video shows exact Codex interactions and Obsidian outputs that help if you plan to replicate it yourself.
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