Senior Full Stack Developer for Construction-Tech SaaS Platform

About the Project SylviSite is a construction site accountability SaaS platform for Indian builders, providing real-time material tracking, GPS-tagged photo proof, planned vs. actual progress tracking, and automated weekly reports via WhatsApp and email. We're looking for a Senior Full Stack Developer to build our Phase 1 platform from the ground up over 12-14 weeks. Tech Stack Frontend/Mobile: React.js, React Native Backend: Python (FastAPI) Database: PostgreSQL, with offline-first architecture (SQLite sync) Cloud: AWS Integration: WhatsApp Business API Key Requirements Strong experience with offline-first mobile architecture (sites often lose network connectivity; app must save locally and sync automatically when connection returns) Experience designing and building REST APIs Comfortable working independently on system architecture, not just executing a spec Prior experience with multi-tenant SaaS platforms preferred Project Structure Fixed-price project, paid in milestones: 20% / 30% / 30% / 20% tied to defined deliverables Full BRD and Scope of Work already finalized and ready to share with shortlisted candidates All code, repositories, and cloud accounts remain under our ownership What We're Looking For Someone who can commit consistently for the full 12-14 week engagement Clear, proactive communication — daily/weekly updates on progress Comfortable with Indian business context and WhatsApp-first communication with end users (site engineers) Please share relevant past projects (especially anything involving offline-first mobile apps, React Native, or FastAPI) along with your proposal.