FairSlice — Expense Splitting for Groups and Game Nights

The Problem

Splitting expenses with friends shouldn’t require a spreadsheet. But existing tools fall short:

• Splitwise handles basic splits but can’t scan receipts, settle poker games, or automate reminders based on debt age
• Venmo/PayPal track payments but not who owes what across multiple expenses
• Group chats turn into “did you pay me?” arguments with no resolution

We needed something that handles the full range — from a restaurant bill split four ways to a weekly poker game with rebuys to recurring rent with roommates.

The Solution

FairSlice is a full-stack expense-splitting platform with AI-powered intelligence.

Expense Splitting — 4 Methods

• Equal — Auto-rounding so no one gets shorted by a penny
• Unequal — Exact amounts when someone had the expensive dish
• Percentage — Split by ownership stake or agreed ratios
• Shares — Weighted splits (2 shares vs 1 share)

Plus: multi-payer support (Alice paid $60, Bob paid $40 for the same expense), itemized restaurant splitting, and expense templates for recurring setups.

AI Receipt Scanning

Snap a photo of any receipt and Claude Vision extracts:

• Merchant name, item list with quantities and prices
• Tax, tip, and total with currency detection
• Confidence scoring for accuracy

Then assign items to people — tax and tip split proportionally. No manual entry needed.

Smart Categorization

Two-tier system: keyword matching across 16 categories (food, transport, housing, etc.) handles most expenses instantly. For ambiguous descriptions, Claude Sonnet classifies them with high accuracy.

Game Session Settlements

Built-in support for poker nights, rummy, teen patti, and more:

• 8 game templates — Texas Hold’em, Rummy, Teen Patti, Spades, Blackjack, Baccarat, Mahjong, 21
• Buy-in + rebuy tracking per player
• Two scoring modes: chip-based (poker) and point-based (rummy/mahjong)
• One-tap settlement — calculates optimized transfers automatically

Debt Simplification

If Alice owes Bob $20, Bob owes Charlie $15, and Charlie owes Alice $10 — FairSlice reduces that to the minimum number of transfers. Never more than N-1 transfers for N people. Uses a greedy matching algorithm pairing largest debtor to largest creditor.

Smart Reminders

Automatic reminders based on debt aging:

• Fresh debts (< 7 days): no reminders
• Normal (7–30 days): remind if amount >= $50
• Aging (30–90 days): remind every 14 days
• Stale (90–180 days): remind every 7 days
• Ancient (> 180 days): remind every 3 days

Financial Insights

• Fairness Score — Gini coefficient measuring how evenly expenses are distributed (0–100)
• Category breakdown — Spending by category per person
• Balance trends — Historical snapshots to track debt aging
• Urgency scoring — Flags important debts by combining amount and age

More Features

• Multi-currency — 150+ currencies with real-time conversion
• Settlement confirmation — Payments require receiver confirmation, eliminating disputes
• 10 payment methods — Cash, Venmo, PayPal, Zelle, UPI, Apple Pay, Google Pay, Interac, Revolut, Wise, crypto
• Friend system — 1:1 expense tracking outside of groups
• Recurring expenses — Auto-create weekly/monthly expenses via cron
• CSV import/export — Bulk migration and GDPR-compliant data export
• Webhooks — Subscribe to 9 event types with HMAC signing and auto-retry
• Global search — Cmd+K search across expenses, groups, and friends

Tech Stack

• Next.js 16 — App Router with 107 API routes
• TypeScript — Strict mode, 250+ type definitions
• React 19 with Tailwind CSS v4
• Supabase — PostgreSQL, Auth, Realtime channels for instant updates
• Anthropic Claude — Vision for receipt scanning, Sonnet for categorization
• Vercel — Edge deployment with daily cron jobs
• Zod 4 — Runtime validation across all API inputs
• Vitest — Testing framework

Security

• Rate limiting across 4 tiers (standard, heavy for AI ops, auth, export)
• CSRF protection with Origin header validation
• Webhook delivery with SSRF protection, HMAC-SHA256 signing, and exponential backoff retries
• Privacy controls for email/phone visibility
• Full account deletion support