(2025-09-15) How To Use Claude Code As A Second Brain

How to Use Claude Code as a Second Brain. While Claude Code is popularly seen as a coding assistant (and he does know how to code), one of Noah Brier’s signature uses is turning it into a research and thinking partner inside Obsidian.

How Brier lays the groundwork for his research assistant

Brier runs Claude Code inside Obsidian (ie at the top of his Obsidian directory, all vaults below)

Brier usually kicks off a new idea by telling Claude Code he’s in “thinking mode,” not “writing mode.” It’s his way of slowing the overeager model down, reminding it to hold off on generating text and instead ask him questions that help him clarify his thinking.

*On the show, Brier takes Dan through his prep work for a talk he’s giving at BRXND, the AI-marketing conference that he runs. For this, Brier gave Claude Code the big points he wants to make and a working title, “Transformers are eating the world,” following the thesis that LLMs are displacing a bunch of specialized code. He also feeds in an anecdote about the Simple Sabotage Field Manual, a relic from World War II, which I was pleasantly surprised to see in a talk about AI and marketing.

Brier then got Claude Code to go to town on his Obsidian, using it to gather relevant bits of information from the vast expanse of his note-taking history*

Once Claude Code has pulled relevant material from Brier’s Obsidian into the vault he created for the talk, he starts to sift and recombine ideas.

According to Brier, “There's entirely too much focus on [AI’s] ability to write and not enough focus on its ability to read… I think arguably [that’s] much more useful on a day-to-day basis. We produce artifacts far less frequently than we just think about things.

Brier also uses a Claude agent to facilitate his thinking. The agent asks him questions, keeps track of them, and maintains a running log of what he’s uncovering in the process.

One of the biggest benefits, he says, is how it helps him pick up where he left off. AI gives him the luxury of being interrupted and then easily resuming by asking it to “catch me up on the last three days of research,

To bring this Claude Code-Obsidian setup onto his phone, Brier uses an app called Termius, which connects to a small computer he keeps running in his basement through Tailscale, a tool that creates a private, secure network so only he can access it. His Obsidian notes are stored in a private GitHub repo, which means he can sync the latest version of his vault onto that computer whenever he needs to.