Calculate fair betting odds for friendly wagers using Brier scoring.
w.ratfr.de — works on any device, no installation needed. See the FAQ in the app for detailed explanations.
Wagers can easily be shared via the URL. Here you can see the wager of the screenshot above.
- 2-8 participants, binary or multi-outcome bets (up to 8 outcomes)
- Fair payouts via Brier scoring (a proper scoring rule that rewards honest predictions)
- Multiple stake types: money (USD, EUR, etc.) or fun stakes (cookies, hugs)
- Share wagers via URL — all data stays in your browser, nothing stored on servers
- PWA: installable, works offline
This app is a PWA — it can be installed on your device and works offline. Once installed, it behaves like a native app with its own icon and window.
To install: Look for an install button in your browser's address bar or menu (often labeled "Install" or "Add to Home Screen") when you visit w.ratfr.de.
Learn more about installing PWAs
Each participant's prediction accuracy is measured with a Brier score (lower = better). Payouts are based on how your score compares to others.
Example: Alice, Bob, and Carol bet $40 on whether it rains tomorrow. Tomorrow comes and it does rain.
- Alice: 70% rain → Brier score 0.18
- Bob: 30% rain → Brier score 0.98
- Carol: 50% rain → Brier score 0.50
Alice predicted best, Bob worst. Result: Alice wins $11.20, Carol wins $1.60, Bob pays $12.80.
The key property: reporting your true belief always maximizes your expected payout.
You can find a detailed calculation example in the FAQ in the app.
See docs/dev/DEVELOPMENT.md for setup and deployment.
All calculations are client-side. No data collection. See docs/dev/SECURITY.md.
MIT — see LICENSE.
Icon by Freepik.