Francisco De Haro
Full-Stack Engineer focused on SaaS, payments and AI integrations
Profile
Full-Stack / Product Engineer focused on TypeScript, Next.js, and PostgreSQL. I have worked on multi-tenant B2B SaaS, Stripe payment integrations, and production AI automations. I am comfortable taking product end-to-end, from data modeling and business logic to delivery and stabilization.
I have worked on broad PostgreSQL data models, Stripe Connect billing flows, and product automations built with OpenAI. I am comfortable in systems where money, sensitive data, and ongoing maintenance all matter.
What I bring
- TypeScript, Next.js, PostgreSQL, and product data modeling
- Multi-tenant B2B SaaS, business logic, and production debugging
- Critical integrations: Stripe Connect, RevenueCat, OAuth, and WebSockets
- OpenAI automations and AI-assisted workflow routing
- iOS/Android apps with Expo and React Native
- Delivery, stabilization, and maintenance of production software
Remote · EU timezone. Open to freelance projects, technical collaborations, or positions where I can build product from day one.
Projects
Saena
Clinical SaaS for therapists
- 179 commits · 560 files · ~106K lines
- Complete clinical calendar: weekly, monthly, 5-day, drag-to-create, drag-to-move, resize
- Stripe Connect: direct onboarding, session billing, QR, auto-charge, 3-layer confirmation
- Real bidirectional Google Calendar sync with echo detection and queue recovery
- Real-time video consultations with LiveKit: secure rooms, per-session tokens
Fantasktic
Multi-tenant B2B SaaS platform · Stupendastic Films (Fos a Blanc SL)
- 307 of 1,033 commits in a 6-developer team · production platform
- Multi-tenant architecture with subdomains, cross-domain OAuth and secure cookies
- Virtualized canvas with thousands of items, sticky headers and requestAnimationFrame
- Google Calendar Sync: dual OAuth, multi-column DATE sync, rate limiting
- Complete Time Clock system: calendar, geolocation, breaks, visual timeline
SAO Psychotherapy
Production clinical platform · Freelance
- Technical financial audit with more than EUR 1,200 recovered and full traceability
- Stripe Connect bug fixes: migration to destination charges, 4-level anti-duplicates
- Atomic webhook stabilization and automatic billing system fixes
- Complete traceability of every euro to Stripe transaction ID
- Multi-system diagnosis and fixes (PostgreSQL + Stripe API + cron jobs + webhooks)
- Published on npm as @deharo/hydra · 30+ CLI commands · 17+ REST endpoints
- Hybrid architecture: local accounts + remote execution with AES-256-GCM encryption
- Bidirectional terminal streaming via WebSocket + node-pty in real time
- Auth with JWT + refresh token rotation + Argon2id hashing
- Organizations with RBAC (owner/admin/member), invitations and full audit trail
- Stripe Connect & Split Payments: Implementation of connected accounts
- Multi-tenant Management: Database architecture in Supabase
- Webhooks & Synchronization: Robust payment event listening system
- Dynamic Pricing Algorithm (Tiered Pricing) for commissions
- Retention Engine (Churn Prevention) for subscriptions
- 100+ users · Organic content with 30K views
- Personalized workout generation with OpenAI API
- Subscription system (monthly, annual, lifetime) with RevenueCat
- Exercise database integrated with Gymvisual
- Progress tracking and statistics
- +21,400 answers · +1,600 questions · 100% organic growth
- Creation and management of personalized multiple-choice exams
- Integrated AI chat with OpenAI for assistance while answering
- User system with Supabase Auth
- PostgreSQL database to store exams and answers
Llama Fine-tuning for Spanish Lyrics
Fine-tuning Llama 3.3 and 3.1 models for music lyrics generation
- Fine-tuning Llama 3.3 (1B/3B) and 3.1 (8B) with QLoRA 4-bit
- Custom dataset of +10,000 prompt-completion examples
- Autonomous scraping pipeline with Playwright for capture and parsing
- Intelligent tokenization with masking (labels=-100 in prompts)
- Optimized training with Unsloth (~2× faster)
Tech Stack
Frontend & Mobile
Backend & Database
Auth & Payments
AI & Machine Learning
DevOps & Tools
Education
Business Administration Degree, Universidad de Murcia (in progress)
Languages
Spanish
Native
English
Advanced
French
Basic
Available immediately for collaborations and new opportunities.
Contact → frandeharo55@gmail.com