Daniel Ruppin

Founded and built DuoByte as Managing Director, leading strategic business development and operational management. Actively involved in full-stack development projects with a specialized focus on web application development using modern technology stacks such as React, TypeScript, Node.js, and AWS cloud infrastructure. Managed technical project execution from conception to deployment while simultaneously overseeing business operations, client relationships, and strategic growth initiatives. Combined entrepreneurial leadership with practical technical expertise to develop innovative web solutions and drive company growth in the competitive technology sector.

Built an administration and appointment scheduling platform for a physician network in the greater Nuremberg area. Multi-stage onboarding flow with practice data, bank details, and multiple specialty selection, 6-digit email verification code with 30-minute validity, and admin approval workflow including live badge in the sidebar. JWT authentication with 15-minute access tokens and rotating 7-day refresh tokens in HttpOnly cookies, plus SHA-256 hashed password reset via email link. Appointment slot system for network-internal referrals: doctors offer appointments with duration and multiple appointment types, other members book them for their patients. Automatic invoice generation per booking with year-based numbering, double-sided issuance to providers and bookers, snapshot of master data, and PDF storage in the database.

Admin area for specialties, invoice issuer master data, member management, and approvals. Geocoding module for practice addresses. Transactional emails (verification, approval, deactivation, password reset) via IONOS SMTP using a shared template. Frontend: React 19, Vite, TypeScript, Tailwind CSS v4, TanStack Query, React Hook Form, Zod, shadcn/ui with Radix Primitives, React Router v7. Backend: Express 5, TypeScript, Prisma 7 with PostgreSQL, Pino logging, Helmet, Zod validation. Deployment via Docker Compose with separate dev and prod stacks behind a shared Caddy reverse proxy, automatic releases via GitHub Actions on dev and prod branches.

Development of a B2B platform for newspaper and digital advertisements, from price list capture to print-ready ad PDFs. AI-powered extraction of publisher price lists using PyMuPDF, pdfplumber, and OpenAI Structured Output to capture titles, editions, packages, columns, ad formats, placements, discounts, surcharges, and digital products; automatic price list monitor with PDF crawling, classification, hash de-duplication, and versioning by source and content date. Public multilingual order flow for ads with template selection, live preview, image upload, square crop, downscaling, and optional client-side background removal. Server-side PDF/X-4 generation for publisher-specific print requirements: InDesign-exported ad templates, synchronized HTML/PDF overlay geometry, embedded MyriadPro fonts, Playwright rendering, pdf-lib overlay, Ghostscript conversion to CMYK, ICC output intent, and trim box/bleed box and trim control per format. Offer management with financial summary, PDF/Excel export, and Bexio offer synchronization. Microsoft OAuth 2.0 SSO with domain restriction, JWT authentication with refresh token rotation, email verification, and API rate limiting. Frontend: Next.js 16, React 19, TypeScript, shadcn/ui, Tailwind CSS v4, Recharts. Backend: Express.js, TypeScript, Prisma ORM, PostgreSQL, Python-extractor. Containerization with Docker Compose and Caddy reverse proxy, CI/CD via GitHub Actions.