CairnOS is private by default: your data lives in a single SQLite file on your machine. A built-in engine classifies natural-language brain dumps into structured items, and a local MCP server lets Claude Code work on the very same data the app uses.

What makes it different

• 🧠 One local brain, shared with Claude Code. The desktop app and a local MCP server read and write the same SQLite database. Ask Claude "what's overdue?" or "make a task to email the team tomorrow," and it shows up live in the app.
• 🔒 Local-first and private. No accounts, no cloud, no telemetry. It works fully offline and your data never leaves your machine. Export to JSON anytime.
• ✨ Brain dump in, structure out. Type one messy stream of thought; CairnOS splits it into tasks, ideas, notes, and reminders with priorities and due dates, for you to review before saving.
• 🤖 AI is optional. A deterministic rule engine works out of the box. Point it at a local Ollama model when you want, with automatic fallback.

Download

Grab the latest Windows installer from Releases. Use the .exe (per-user, self-updating). It isn't code-signed yet, so Windows may warn "Unknown Publisher": click More info → Run anyway.

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Why it's built this way

Tauri's UI runs in a webview and can't open a native SQLite file directly, and the MCP server is a separate Node process that must share that same database. So a small local engine (apps/server, Hono) owns the SQLite file and exposes a typed API. The result:

                          ┌────────────────────────┐
   Desktop UI (React) ───▶│  @cairn/server (Hono)  │
   TanStack Query / SSE   │     local engine       │──┐
                          └────────────────────────┘  │   ┌──────────────┐
                                                       ├──▶│  cairn.db    │  (SQLite + WAL)
   Claude Code ──stdio──▶ @cairn/mcp-server ───────────┘   └──────────────┘
                          (same @cairn/core + DB)

• One brain, one database. @cairn/core holds every service; both the engine and the MCP server call it, so the app and Claude always agree.
• Runs in your browser today (pnpm dev) with real SQLite persistence - no Rust required.
• Tauri wraps it into a native window when you want to ship a desktop binary.

Tech stack

Tauri v2 · React 18 · TypeScript (strict) · Vite 6 · Tailwind CSS v4 · shadcn-style UI · SQLite + Drizzle ORM · Hono · TanStack Query · Zustand · Zod · date-fns · Framer Motion · lucide-react · Model Context Protocol SDK · Vitest.

Monorepo layout

cairn/
├─ apps/
│  ├─ desktop/      # React + Vite UI (+ src-tauri native shell)
│  ├─ server/       # @cairn/server - local Hono engine that owns the DB
│  └─ mcp-server/   # @cairn/mcp-server - local MCP server (13 tools)
├─ packages/
│  ├─ shared/       # enums, domain types, Zod validators
│  ├─ db/           # Drizzle schema, migrations, client, seed
│  └─ core/         # services + the rule-based classifier
└─ docs/            # product spec, architecture, database, design system, MCP setup

Quickstart

Prerequisites: Node 20+ and pnpm 10+. (Rust is only needed for the native Tauri build.)

pnpm install          # install the workspace
pnpm db:migrate       # create the local SQLite schema
pnpm db:seed          # optional: realistic sample data
pnpm dev              # start the engine + the web UI

Then open http://localhost:5173. The marketing page is at http://localhost:5173/#/landing.

The database is created at %APPDATA%\Cairn\cairn.db on Windows (~/Library/Application Support/CairnOS on macOS, ~/.local/share/CairnOS on Linux). Override with CAIRN_DB_PATH or CAIRN_DATA_DIR.

Commands

Command	What it does
pnpm dev	Run the local engine and the web UI together.
pnpm server:dev	Run only the engine (port 4319).
pnpm web:dev	Run only the Vite UI (port 5173).
pnpm desktop:dev	Run the native Tauri app (requires Rust).
pnpm desktop:build	Build a native desktop binary (requires Rust).
pnpm mcp:dev	Run the local MCP server (stdio).
pnpm db:generate	Generate a Drizzle migration from the schema.
pnpm db:migrate	Apply pending migrations.
pnpm db:seed	Seed sample data (CAIRN_SEED_FORCE=1 to reseed).
pnpm typecheck	Typecheck every package.
pnpm build	Production build of the web UI.
pnpm --filter @cairn/core test	Run the classifier unit tests.

The brain dump

Type something messy into Quick Capture (⌘/Ctrl + K → Quick capture):

tomorrow finish the launch deck, fix the signup bug, idea for referral rewards, remind me to email the team, prepare the Monday demo

CairnOS extracts five reviewable items - a task due tomorrow, another task, an idea, a reminder, and a task - each with a detected priority, due date, project suggestion, and a confidence score, before you save. The classifier lives in packages/core/src/classifier and is modular: swap it for a local Ollama model or the Claude API behind the same classifyBrainDump signature.

Connect Claude Code (MCP)

Register the server once at user scope so it's available in every Claude Code session, from any folder:

claude mcp add cairn --scope user -- pnpm -C /path/to/cairnos --filter @cairn/mcp-server start
claude mcp list            # → cairn ✔ Connected

Now ask Claude "what are my overdue tasks?" or "create a task to email the team tomorrow at 9am." Full guide (incl. project-scope .mcp.json for sharing the repo, and Claude Desktop config): docs/mcp-setup.md.

Native desktop (Tauri)

The native shell lives in apps/desktop/src-tauri and is wired up with app icons and the notification plugin. It needs the Rust toolchain and the platform WebView (WebView2 on Windows, already standard on Win 11). Then:

pnpm desktop:dev      # opens the native CairnOS window

desktop:dev auto-starts the engine + UI for you (via Tauri's beforeDevCommand), so you don't need a separate pnpm dev.

Standalone installer

pnpm desktop:build

This produces a fully self-contained installer - no Node, no repo required to run it:

• …/target/release/bundle/nsis/CairnOS_0.1.1_x64-setup.exe (~27 MB)
• …/target/release/bundle/msi/CairnOS_0.1.1_x64_en-US.msi (~40 MB)

The build bundles the engine as a sidecar: a matching node.exe, the esbuild-bundled engine, the better-sqlite3 native addon, and the migrations are shipped as Tauri resources (scripts/build-engine.mjs). On launch the Rust app spawns the engine (self-migrating, on localhost:4319) and shuts it down when the window closes. Data still lives in %APPDATA%\Cairn\cairn.db, so the MCP server and the installed app share it.

Optional power-ups

All off by default - the app is fully functional without them.

Local AI classifier (Ollama). Point the brain dump at a local model instead of the rule engine. Install Ollama, pull a model, then:

# PowerShell
$env:CAIRN_CLASSIFIER="ollama"; $env:CAIRN_OLLAMA_MODEL="llama3.2"; pnpm dev

It falls back to the rule engine automatically if Ollama is unreachable. (The deterministic date parser still resolves due dates, so the model never does date math.)

Local semantic search. Rank search by meaning using on-device embeddings - no API, no cloud:

pnpm --filter @cairn/server add @huggingface/transformers
$env:CAIRN_SEARCH="semantic"; pnpm dev

First query downloads a small model (~25 MB) and caches it; failures fall back to the built-in ranked search.

Theme. Settings → Appearance switches dark / light / system live (dark is the default).

Docs

• Product spec
• Architecture
• Database
• Design system
• MCP setup

Privacy

Everything is local. There are no accounts, no telemetry, and no network calls in the MVP. Export all of your data as JSON from Settings → Export data.