Second Brain

A local-first, multiplayer research notebook with a CRDT editor and AI cells.

ProseMirror · Yjs · React 19 · FastAPI · Claude

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A cell-based notebook — think Notion meets Jupyter — built on a hand-rolled ProseMirror editor and Yjs CRDTs for real-time, offline-first collaboration. Cells can be rich markdown, an AI conversation (Claude, streaming, with RAG over your notes), or a weekly planner. Everything syncs across tabs and devices and keeps working offline.

Built as a deep portfolio project around a rare combination: editor engineering + CRDT collaboration + AI integration. See documents/ for the architecture.

1. Main page with multiple cursor:

2. AI Report based on Weekly planner:

3. AI cell formatting:

Why it's interesting

• Raw ProseMirror, no Tiptap — full control over the schema (doc → cell → block), custom NodeViews that embed React, slash menu, and a floating formatting toolbar.
• Real CRDT collaboration — Yjs is the source of truth; multiplayer cursors, offline edits, and conflict-free merge. Backed by convergence tests.
• Time-travel — Y.snapshot history with restore, including the AI/planner side-data.
• AI that knows your notebook — streaming Claude replies with 3-tier context retrieval (local cells → doc → cross-doc RAG via pgvector), extended thinking, web search, vision (paste images), and a local Ollama option for privacy.
• Durable & private — Neon Postgres is the real source of truth; the Anthropic key never ships in the browser (a backend reverse-proxy injects it).

Tech stack

Layer	Stack
Editor	ProseMirror (raw), React 19, TypeScript, Zustand
Collaboration	Yjs, y-prosemirror, y-indexeddb, y-websocket
AI	Anthropic Claude SDK (streaming), Ollama (local), pgvector RAG
Backend	FastAPI, SQLAlchemy (async), Neon Postgres + pgvector, sentence-transformers
Build / i18n	Vite, Vitest, react-i18next (EN/VI)
Hosting	Vercel (frontend) · Fly.io (backend + sync relay)

Architecture at a glance

flowchart LR
  subgraph Browser
    PM[ProseMirror editor]
    Y[Yjs Y.Doc<br/>source of truth]
    R[React UI + NodeViews]
    PM <--> Y
    R <--> Y
  end
  Y <-->|real-time| WS[y-websocket relay]
  Y -->|binary state| BE[FastAPI backend]
  R -->|/anthropic proxy| BE
  BE --> NE[(Neon Postgres<br/>+ pgvector)]
  BE -->|reverse-proxy| CL[Claude API]

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Full write-up: documents/architecture.md.

Quick start

Prerequisites: Node 20+ with pnpm, Python 3.11+, a Neon Postgres database (with the vector extension), and optionally Ollama for local AI.

# 1. Frontend
pnpm install
cp .env.example .env.local        # adjust URLs if needed
pnpm dev                          # → http://localhost:5173

# 2. Sync server (real-time collab) — separate terminal
pnpm dev:ws                       # → ws://localhost:1234

# 3. Backend (RAG, persistence, Claude proxy) — separate terminal
cd backend
python -m venv .venv && .venv/Scripts/activate   # (Unix: source .venv/bin/activate)
pip install -r requirements.txt
cp .env.example .env              # set DATABASE_URL + ANTHROPIC_API_KEY
uvicorn app.main:app --reload     # → http://localhost:8000

The app runs frontend-only too — collaboration falls back to local IndexedDB, and AI/RAG features are simply disabled until the backend is up.

Environment variables

Scope	Variable	Purpose
Frontend	VITE_BACKEND_URL	FastAPI base URL (default http://localhost:8000)
Frontend	VITE_WS_URL	y-websocket relay (default ws://localhost:1234)
Frontend	VITE_OLLAMA_URL	local Ollama daemon (default http://localhost:11434)
Backend	DATABASE_URL	Neon Postgres connection string
Backend	ANTHROPIC_API_KEY	Claude key (server-side only)
Backend	ALLOWED_ORIGINS	comma-separated CORS origins

Scripts

pnpm dev          # Vite dev server
pnpm dev:ws       # y-websocket sync relay
pnpm dev:backend  # FastAPI (Windows venv path)
pnpm test         # Vitest (CRDT convergence tests)
pnpm build        # tsc -b && vite build
pnpm lint         # ESLint
pnpm format       # Prettier

Project structure

src/
  schema.ts        ProseMirror schema (doc → cell → block) + marks
  commands.ts      editor commands (insert / transform / select)
  collab/          Yjs setup, AI threads, snapshots, weekly plans, streaming
  plugins/         slash menu, placeholder, selection, image paste, …
  nodeViews/       React-backed cells (AI, markdown, weekly)
  components/      sidebar, toolbars, modals, language switcher
  hooks/           useNotebookEditor, useDocRegistry
  lib/             config, http, backend sync, image resize, markdown io
  i18n/            react-i18next (en / vi)
  styles/          design-system tokens + per-component CSS
backend/           FastAPI + Neon + pgvector
deploy/            Fly.io configs (backend + sync relay)
documents/         architecture & subsystem docs  ← start here

Documentation

Doc	What it covers
Architecture	System overview, data flow, key decisions
Editor (ProseMirror)	Schema, NodeViews, commands, plugins
Collaboration (Yjs)	CRDT model, sync, offline, snapshots
AI	Streaming, RAG, vision, providers
Backend	FastAPI, persistence, RAG, reverse-proxy, images
Deployment	Vercel + Fly.io

Testing

pnpm test

CRDT correctness is covered by convergence tests: two/three simulated peers edit concurrently and the docs must converge byte-identically.

Status

Actively developed. Core editor, real-time collaboration, AI cells, RAG, and deployment are in place; see the docs for what's solid and what's still evolving.