Full Stack Developer & AI. I build products with real traction. From idea to users in weeks.
Testum: +21,400 student responses, 100% organic growth. Canivos: fintech infrastructure for NGOs in production. Repai Trainer: iOS app published with subscriptions. End-to-end full-stack (Next.js, React Native, Supabase, PostgreSQL). Short cycles, results-focused, products people actually use.
Featured projects
A collection of projects I've worked on, from web applications to AI integrations.
Promecenas
Promecenas is a technology platform that allows NGOs to digitize their management, increase their visibility, and optimize their monetization through an advanced sponsorship and donation system. The model is 100% free for NGOs (no fixed monthly costs). The platform is sustained solely by transaction commissions on donations and sponsorships, aligning the platform's incentives with the fundraising success of the organizations.
B2B Fintech Infrastructure for General NGOs.
Repai Trainer
Repai Trainer is a personalized AI-powered training mobile application, available on the App Store. Fully developed by me from scratch, it combines a native iOS frontend with Expo/React Native, a robust Supabase backend, subscription system with RevenueCat, and workout generation using OpenAI API. The app allows users to create personalized routines, track their progress, and receive intelligent exercise recommendations based on their goals and performance.
Personal project currently on development pause.
Testum
Testum is a web platform developed with Next.js that allows creating and taking multiple-choice exams quickly and effectively. Users can upload their own exams and solve them with a highly polished UX experience. The project reached +1600 questions to solve and +21400 accumulated answers, spread solely by word of mouth among students of the Business Administration degree at my university. It includes an integrated AI chat with OpenAI to help users while answering, authentication with Supabase, and PostgreSQL database to store all information.
Personal project developed for Business Administration students at my university.
UMChat - Advanced Chat System
UMChat is an intelligent chat web application built from scratch with a complete system for managing conversations, documents and authentication. The project demonstrates expertise in modern full-stack development, complex data architecture and performance optimization. Includes AI integration, automatic OCR, intelligent file deduplication, real-time streaming, and an architecture of 8 tables with complex relationships. Built with Next.js 14.2, React 18.3, TypeScript, PostgreSQL with Supabase, and multiple external APIs.
Personal project representing the evolution of Testum towards a complete conversational platform.
Canivos (Now Promecenas)
Canivos is not just an adoption website; it is a vertical SaaS solution designed to digitize animal shelters with zero fixed costs. The platform operates under a Financial Marketplace model, using Stripe Connect to route donations, calculate dynamic commissions in real-time, and manage recurring subscriptions, eliminating administrative friction for NGOs.
B2B Fintech Infrastructure for NGOs.
TeSuena - Guess the Song
Full-Stack music game project demonstrating advanced skills in modern web development, streaming API integration, real-time systems, and scalable architecture. Includes Single Player (Classic), Daily Challenge (Wordle-style), and Versus (Online Multiplayer) game modes.
Personal Full-Stack project.
Demo Mistral Chat
A modern chat web application that demonstrates Mistral AI capabilities. Built with Next.js 14 and deployed on Vercel Edge, it implements real-time response streaming for a fluid and responsive user experience. The project explores best practices for integrating LLMs into web applications, including context handling, prompt optimization, and efficient conversation state management.
Llama Fine-tuning for Spanish Lyrics
Fine-tuning project of Llama models (3.3 1B/3B and 3.1 8B) to produce coherent Spanish song lyrics with consistent structure, rhyme, and theme. Optimized to balance quality and cost through advanced techniques like QLoRA 4-bit and Unsloth. The project includes a complete custom scraping pipeline developed with Playwright to create a robust dataset of +10,000 prompt-completion examples, intelligent tokenization system with masking, and efficient training architecture with A100 achieving high-quality results with ~24.3M trainable parameters.
Personal experimentation project with LLM fine-tuning. Training performed with A100 GPU.
LoRA Black Stories - Image Generation
LoRA adapter training project to replicate the characteristic visual aesthetic of "Black Stories" and generate new stories/scenes with visual consistency. The project includes meticulous dataset curation, autocaptioning system to strengthen style, trigger word definition for precise style control through prompts, and multi-resolution training (512-1024) to improve generalization. It includes a rigorous aesthetic QA process reviewing composition, silhouettes, contrast, contours, and coherence between samples to ensure stable and reproducible aesthetics. Trained on Black Forest Labs FLUX models (flux-schnell and flux-dev).
Personal project for own use in image generation and style control experimentation.
1¢, 1min, 100%: AI in University Exams (In Development)
Opensource research paper on the application of artificial intelligence models to Business Administration and Management exams at the University of Murcia, Spain. Results and methodology are publicly available. Results demonstrate that advanced reasoning models (OpenAI API, xAI API, Google AI API) achieve 100% accuracy in less than 1 minute per exam, with an approximate cost of 1 cent per evaluation. This study includes the development of an OCR system implemented with Mathpix API and LATEX/Markdown conversion program to automate exam processing. SQLite database with Prisma for efficient data management.
Academic research in development. Results are preliminary and subject to review.
Personal Portfolio
This website. Personal portfolio built with Next.js 14 App Router, TypeScript, and Tailwind CSS. Minimalist dark mode design.
CV
Experience, tech stack, and education.
Contact
Summary
Full-stack developer with 3 years of experience in own products and freelance. Specialized in Next.js, React Native and AI integration in production. App published on App Store with subscriptions and complete backend. Experience in code auditing and bug resolution in large codebases (+300K lines). Immediate availability.
What I bring
- Technical consulting and bug resolution in production
- iOS/Android mobile apps with Expo and React Native
- Production AI API integration (LLMs, image generation)
- Payments and subscriptions: Stripe, RevenueCat, App Store Connect
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
About me
I enjoy building products from scratch and seeing real people use them. Testum started as a personal project for my exams and ended up with over 21,000 responses from classmates, all word of mouth. That taught me more than any course: if a product solves a real problem, people find it. I work fast, iterate based on feedback, and prefer shipping something imperfect over perfecting something no one will use. I'm in my third year studying Business Administration but spend more time coding than in class.
Preguntas Frecuentes
¿Quién soy?
Soy Francisco De Haro Martínez, Desarrollador Full Stack y experto en integración de Inteligencia Artificial en España. He creado aplicaciones como Repai Trainer y Testum, especializándome en tecnologías como Next.js, React Native y Supabase.
¿En qué tecnologías trabajo?
Mi stack principal incluye TypeScript, Next.js, React, React Native (Expo) y PostgreSQL. Además, soy experto en la integración de modelos de lenguaje (LLMs) como OpenAI, Mistral y Llama en productos de producción.
¿Cómo contactar conmigo?
Puedes contactar directamente a través de mi email frandeharo55@gmail.com.
Availability: Remote · EU timezone. Open to freelance projects, technical collaborations, or positions where I can build product from day one.
Available for collaborations → frandeharo55@gmail.com
