The "second brain" concept is simple: capture everything you learn, organize it so you can find it later, and connect ideas across topics. Most people reach for tools like Notion, Roam, or Obsidian to do this. But you can build a second brain with nothing more than a folder of markdown files — and it might be the most durable approach of all.

Why Plain Markdown

Every note-taking tool eventually shuts down, changes pricing, or pivots in a direction you don't like. When that happens, your notes are trapped in a proprietary format. Exporting is always possible in theory, but the links break, the formatting shifts, and the metadata disappears.

Markdown files are plain text. They'll be readable on every operating system, with every text editor, for as long as computers exist. Your second brain should outlast any single app.

The Folder Structure

Keep it simple. A flat or shallow folder structure works better than deep nesting:

second-brain/
├── inbox/           — Quick captures, unsorted
├── projects/        — Active project notes
├── areas/           — Ongoing responsibilities (health, finance, career)
├── resources/       — Reference material by topic
└── archive/         — Completed projects, old notes

This follows Tiago Forte's PARA method, but adapted for the file system. Each note is a single .md file. The folder tells you the note's current status. When a project wraps up, move its notes to archive/.

Capturing Notes

The key habit is capturing ideas before they disappear. When you read something interesting, have a thought in the shower, or learn something in a meeting — write it down in a markdown file in inbox/.

The note doesn't need to be polished. A few bullet points with a descriptive filename is enough:

# API rate limiting patterns

- Token bucket is the most common approach
- Sliding window more accurate but higher memory cost
- Redis works well for distributed rate limiting
- Look into: Cloudflare's approach to rate limiting at edge

Save it as api-rate-limiting-patterns.md in your inbox. Later, when you have a few minutes, sort it into the right folder and add any connections to other notes.

Linking Notes Together

You don't need a tool with backlinks to connect ideas. Markdown's link syntax works fine:

See also: [API rate limiting patterns](../resources/api-rate-limiting-patterns.md)

These relative links work in any markdown viewer. If you use a tool like OpenMark to read your files, the links are clickable — tap one and you jump to the connected note.

Over time, your most valuable notes will have several links pointing to and from them. These are your "hub" notes — the ideas that connect multiple areas of your knowledge.

Searching Your Brain

The real power of a markdown second brain emerges when you can search it. On macOS, learn how to use Spotlight search for markdown to find files instantly. Type a few words into Spotlight and find any note instantly, regardless of which folder it's in (OpenMark includes a Spotlight Importer).

You can also use the terminal: grep -r "rate limiting" ~/second-brain/ finds every mention across all your notes in milliseconds.

The Long Game

The best second brain is the one you'll still be using in ten years. Proprietary tools come and go, but the plain text movement shows that markdown files are forever. Start with a folder, a simple structure, and the habit of writing things down. The system grows naturally from there.

No subscription required. No account to create. No data to migrate when the next shiny tool launches. Just your thoughts, in plain text, on your computer.