A pay-per-message AI chat frontend. Billing happens directly in Bitcoin sats via Cashu ecash, routed through the Routstr protocol — no accounts, no subscriptions, no stored payment method.

Live demo: https://moutstr.vercel.app

Features

Chat UI with conversation history, starring, and search
Cashu wallet — paste an existing token or fund via Lightning invoice
Live model catalog fetched from Routstr, with real per-token sats pricing
Pre-flight balance checks before sending, so unaffordable requests are blocked rather than charged
Automatic change handling — unspent sats returned by the API (X-Cashu header) are folded back into the wallet balance

Tech Stack

React 19, Vite
Zustand for wallet, chat, and model state
Dexie (IndexedDB) for local persistence
TanStack Query for polling Lightning invoice settlement
Cashu TS for ecash token handling

Getting Started

npm install
npm run dev

The app talks directly to the Routstr API and to your Cashu mint — no backend of your own is required.

Scripts

npm run dev      # Start dev server
npm run build    # Build production assets to dist/
npm run preview  # Preview the production build locally
npm run lint     # Lint

Project Structure

src/pages/: top-level views (chat list, chat view)
src/components/: UI components (header, model picker, wallet modal, toasts)
src/hooks/: wallet, chat, and Lightning invoice logic
src/utils/: Routstr API client, Cashu helpers, Zustand stores

Balance Safety

Three layers prevent sats from being spent without value received:

A pre-flight estimate (estimateMinSats in src/utils/modelStore.js) checks the selected model is affordable before anything is sent.
Each request is capped with max_tokens, computed from the user's real balance (computeSafeMaxTokens in src/utils/routstr.js), bounding worst-case cost.
If the provider still rejects a request (HTTP 402), the token is not spent — handled in src/hooks/useChat.js.