What You’re Building

You’ll have:

• A local ~/.gbrain/brain.pglite database — embedded Postgres 17 (via WASM) with pgvector, no server config.
• A small “brain repo” of markdown notes about people, companies, and concepts.
• A working hybrid-search CLI that combines vector + BM25 keyword + Reciprocal Rank Fusion (RRF), with a ZeroEntropy reranker on top by default.
• A typed knowledge graph (works_at, founded, invested_in, attended, advises, mentions) auto-extracted from your notes.
• An MCP server exposing 74 tools so Claude Code, Cursor, and Windsurf can read and write to the brain directly.

Prerequisites

• macOS or Linux (Windows users: use WSL2).
• A code editor.
• Bun ≥ 1.3.10 (the runtime GBrain ships on; the repo’s package.json declares this as the minimum engine). We’ll install it in Step 1.
• An embedding API key from one of: ZeroEntropy, OpenAI, or Voyage. Without one, you can still install and run keyword search, but gbrain query (hybrid + vector) will return no results.
• Optional: an Anthropic API key for multi-query expansion during search.

Step 1 — Install Bun and GBrain

To install GBrain:

bun install -g github:garrytan/gbrain
gbrain --version
# gbrain 0.38.2.0

Step 2 — Initialize Your Brain

To initialize your brain:

gbrain init --pglite

This provisions a local PGLite database in ~/.gbrain/. PGLite is full Postgres compiled to WASM — no server, no Docker, ready in roughly two seconds.

Step 3 — Create a Tiny Brain Repo

The brain repo is just a directory of markdown files. Each file follows GBrain’s compiled truth + timeline pattern: a current best-understanding section on top, an append-only evidence trail below.

• Note: wikilinks must use the full slug path (e.g., [[people/alice-chen]], not just [[alice-chen]]) for the graph extractor to resolve them. This is a real gotcha — I tested both forms; the short form silently produces zero links.
• Create a person page:

mkdir -p ~/my-brain/people ~/my-brain/companies ~/my-brain/concepts
cd ~/my-brain

To create a person page:

cat > people/alice-chen.md <<'EOF'
---
type: person
title: Alice Chen
tags: [founder, ai-infra]
---

Founder and CEO of [[companies/acme-ai]]. Previously staff engineer at
Google Brain. Focus area: inference optimization for small language models.

---

- 2024-03-12: Met at AI Engineer Summit. Discussed sparse MoE routing.
- 2024-09-04: Announced $12M seed led by Sequoia.
- 2025-01-18: Shipped open-source inference router on GitHub.
EOF