Lumen

An AI doc editor that doesn't charge you rent.

I was tired of paying monthly subscriptions for AI writing tools that are, underneath it all, a text box plus an API call. So I built Lumen: a local-first markdown workspace where you bring your own API key and pay only for the tokens you actually use — no account, no cloud, no middleman marking up inference.

The idea

• BYOK (Bring Your Own Key). Plug in your OpenAI or Anthropic API key in Settings. Lumen talks directly to the provider on your behalf — a few cents of usage instead of a $20/month plan. Your key is stored in your browser's IndexedDB and only ever sent as the auth credential on your own AI requests.
• Local-first. Folders, documents, and settings live entirely in your browser (IndexedDB). No server database, no sync, no telemetry. Import/Export moves your whole workspace as a single JSON file.
• AI with a seatbelt. Summarize, rewrite, expand, Q&A, and full-document edits with a diff preview — and a guardrail that asks clarifying questions before any action that would substantially overwrite your work.

Tech stack

• Frontend: React + TypeScript + Vite, Tailwind CSS + shadcn/ui, TanStack Query, Zustand
• Storage: Dexie (IndexedDB), with an automatic in-memory fallback when the browser blocks it
• Server: A tiny Express proxy whose only job is forwarding AI requests (official openai / @anthropic-ai/sdk clients) — credentials come from each request, never from the server
• Editor: Markdown with a formatting toolbar, Write/Preview tabs, and a diff view for AI edits

Run it

Requires Node 20+.

npm install
npm run dev   # http://localhost:5050

Build for production: npm run build && npm start.