Co-Split

Project Vision

Co-Split allows groups of friends to manage shared digital services (Netflix, Spotify, etc.) without automated payment gateways. It focuses on transparency, granular service membership, and manual payment tracking.

The platform solves a common problem: when friends share subscription costs, it’s hard to keep track of who owes what, especially when not everyone participates in every service and billing cycles vary.

Core Functionality

Technical Architecture

Monorepo Structure

Co-Split is built as a TypeScript monorepo using npm workspaces, enabling tight integration between frontend, backend, and shared type definitions:

co-split/
├── frontend/       # React + Vite client application
├── backend/        # Firebase Functions (Node.js + Express)
├── shared/         # Shared TypeScript types
└── package.json    # Root npm workspaces configuration

Technology Stack

Frontend:

• React 19 with Vite for fast development and optimized builds
• TypeScript for type safety across the application
• Vanilla CSS with modern, glassmorphic design system
• React Hooks for state management (useState, useMemo)
• Current Status: Fully functional with mock data, ready for backend integration

Backend:

• Firebase Functions running Node.js 20
• Express.js REST API framework
• Firestore NoSQL database for scalable data storage
• TypeScript with strict type checking
• Current Status: Complete REST API implemented, ready for deployment

Shared Types:

• Centralized type definitions via @co-split/shared package
• Domain models (User, Group, Service)
• API contract types (requests/responses)
• Ensures type safety between frontend and backend

Key Design Decisions

No Payment Processing: Co-Split is strictly a cost-tracking dashboard. There are no automated payments, credit cards, or financial transactions—just transparency and clarity about who owes what.

Granular Control: Users are not automatically enrolled in all services within a group. Each person explicitly chooses which services they want to participate in, giving fine-grained control over their commitments.

Monthly Normalization: All billing cycles are converted to monthly equivalents for consistent budgeting, while preserving the actual billing cycle information.

REST API Reference

The backend exposes a RESTful API for all core functionalities:

Groups:

• POST /api/groups - Create a new group
• GET /api/groups?userId={userId} - Get all groups for a user
• GET /api/groups/:groupId - Get group details
• POST /api/groups/:groupId/join - Join a group via invite code

Services:

• POST /api/services - Create a new service
• GET /api/services?groupId={groupId} - Get all services for a group
• POST /api/services/:serviceId/join - Join a service
• DELETE /api/services/:serviceId/leave - Leave a service

Users:

• GET /api/users/:userId/summary?groupId={groupId} - Get financial summary

Design Philosophy

MXM Consulting Delivery Scope

Co-Split demonstrates MXM Consulting’s modern web application capabilities:

• TypeScript Monorepo Architecture with shared type safety across frontend and backend
• Modern React Development with React 19, Vite, and functional programming patterns
• Firebase Cloud Platform with Functions, Firestore, and Authentication
• REST API Design with Express.js and proper error handling
• Responsive UI/UX with glassmorphic design, dark mode, and accessibility
• Mathematical Precision in cost calculations and normalization algorithms
• Scalable Data Architecture with NoSQL patterns and efficient queries