RentMan

RentMan is a full-stack SaaS property management platform built for the Brazilian rental market. It handles the full lifecycle of rental contracts: IGPM/IPCA annual adjustments, late-fee and monthly-interest penalty calculations (with Brazilian business-day logic), IPTU installment tracking, and a smart alert system for upcoming deadlines.

AI Features

• OpenAI Codex contract extraction — Users authenticate with their ChatGPT account via OAuth PKCE flow, then upload a PDF or photo of a rental contract. Codex extracts structured JSON: address, tenant CPF/CNPJ, lease dates, rent amount, adjustment index, guarantee value, IPTU info, penalty rates. Eliminates manual data entry for onboarding. Rate-limited to 5 extractions/user/day.
• MCP server — A full Model Context Protocol server exposes 40+ operations (list/view/create/update/delete contracts, record payments, apply adjustments, view alerts, manage IPTU) so Claude and other AI clients can manage properties via natural language.

Financial Domain Engineering

• Penalty calculation engine — Computes late fees and monthly compound interest based on days overdue, accounting for Brazilian business days (weekends + national holidays excluded).
• Rent adjustment history — Immutable historical record of rent changes. DISTINCT ON queries fetch the effective rent for any past month without denormalization.
• Alert deduplication — Per-contract, per-alert-type dismissal system prevents notification fatigue while maintaining full alert history for audit.
• Batch query optimization — getRentForMonthBatch() pre-fetches historical rents for all contracts in a single query, avoiding N+1 on the dashboard.

Engineering Highlights

• PKCE-secured OpenAI OAuth — Proof-Key-for-Exchange implementation for secure ChatGPT authentication without exposing client secrets. Client-side JWT decoding extracts OpenAI account IDs from access tokens.
• SSE streaming — Real-time streaming responses from Codex parsed and rendered incrementally as the AI extracts contract fields.
• Zero-dependency rate limiter — In-memory sliding-window rate limiter works in both Edge Runtime (middleware) and Node.js without Redis or external services.
• Remotion video generation — Marketing videos (landscape 16:9 and Instagram vertical) rendered programmatically from React components via Remotion 4.
• Bilingual (PT/EN) — Context-based i18n system with 200+ translation keys covering all UI text, error messages, and labels.

Deployment

Vercel (Next.js 16 + React 19 + TypeScript). Supabase PostgreSQL with connection pooling. Stripe for subscription billing ($9.99/mo Pro, 45-day free trial). PostHog for privacy-respecting analytics with cookie consent.

Platform

Web only — responsive design works on mobile browsers. No native iOS/Android or Mac app.