Open to work

Backend Developer. I turn ideas into complete web applications: polished interfaces, solid backend, and code built to last. Every project is an excuse to learn something new.

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Rock 'n code 🤘

sergio@dev:~
~$ whoamiconst dev = { name: "Sergio Zarcero", role: "Backend Dev", location: "Madrid, ES", status: "open_to_work",};
01.

about me

I'm Sergio, a backend developer with over a year of experience in Java. I work as a freelance developer building custom web projects for clients across different sectors, from initial design through to final delivery.

I also spent time at Minsait, where I worked in Java on a large-scale corporate document management system. I like well-organized code: clean architecture, SOLID principles, and projects that are maintainable and scalable. I've worked both in backend (Java, NestJS, Laravel) and frontend (React), always with dockerized environments and version control from the first commit.

This is a marathon, not a sprint, and I don't like falling behind — so I use AI as an assistant in my work (SDD, LLMs), always applying my own judgment and staying in the driver's seat. I speak native Spanish and advanced English, and I'm looking to keep growing with national and international mobility, with a particular interest in international projects. And when I'm not coding, I'm probably listening to rock.

location
Madrid, Spain
target role
Backend Developer
languages
Spanish (native), English (advanced)
education
Higher Vocational Training – Web App Dev. (2024–2026)
status
Open to work
02.

tech stack

Java Backend +1 year exp.

Java Spring Boot

Backend +6 months exp.

PHP Laravel NestJS

Version Control +1 year exp.

Git GitHub

Databases +1 year exp.

SQL

DevOps +6 months exp.

Docker

AI-Assisted Development +6 months exp.

SDD LLMs

Frontend +6 months exp.

TypeScript React
03.

projects

Proclade

Web platform for a nonprofit foundation

Full-stack web platform built as a team for the Proclade foundation: role-based authentication, an admin panel, and a chatbot with its own knowledge base. Fully dockerized monorepo with Nginx as a reverse proxy.

  • Role-based authentication and authorization (admin / user)
  • Admin panel to manage the platform's content
  • Chatbot with a knowledge base loaded at startup
  • 100% dockerized dev environment: API, frontend, and proxy
  • Nearly 300 commits of teamwork with technical documentation
React NestJS Prisma PostgreSQL TypeScript Vite Docker Nginx

Music Band App

Management platform for a music band and its school

Application for managing a music band and its associated school: a Spring Boot REST API and an Angular SPA. Musicians access their events and sheet music; administrators manage users, groups, content, and permissions.

  • JWT authentication in an HttpOnly cookie with CSRF protection and per-role permissions
  • Backend organized by feature (controllers, services, and JPA repositories)
  • Flyway migrations and optimistic concurrency checks
  • Integration tests with Testcontainers (PostgreSQL) and Angular unit tests
Java 21 Spring Boot 3.5 Spring Security Spring Data JPA PostgreSQL Flyway Angular TypeScript Docker Compose

other projects

Lupis Insani

Real-time multiplayer browser game

Web adaptation of Los Hombres Lobo de Castronegro (a Spanish Werewolf-style party game): real-time multiplayer matches over WebSockets, game logic processed asynchronously with queues and workers, and a dockerized environment with six orchestrated services.

Laravel 12 PHP TypeScript MariaDB Redis WebSockets Docker Nginx

Gestión Médica API

REST API for managing medical appointments

REST API for managing medical appointments: patients, doctors, specialties, and scheduling, with role-based authentication and authorization. Layered architecture (model, service, controller) with interactive Swagger documentation.

Java 21 Spring Boot 3.5 Spring Security JWT PostgreSQL springdoc-openapi Docker

Stars Battle

Turn-based, Star Wars-themed battle API

Turn-based battle API: register, pick a character, fight PVE against a machine opponent or PVP against another player, and climb the ranking. A from-scratch architectural rebuild of 'Batalla Friki' (NestJS + Prisma), replicating the same domain rules in Java 21 / Spring Boot 3, built with strict TDD.

Java 21 Spring Boot 3.5 PostgreSQL JWT WebSocket (STOMP) springdoc-openapi Maven

See all repositories on GitHub →

04.

experience

  1. Jun 2025 — Present

    Freelance Developer

    Custom web development for clients across different sectors.

    Backend Java REST APIs Freelance

  2. Mar 2026 — May 2026

    Backend Java Developer

    Minsait

    I worked in Java on a large-scale corporate document management system, integrated into the technical team and adapting to their working methodologies.

    Java Backend Web services

  3. 2024 — 2026

    Higher Vocational Training – Web Application Development (DAW)

    Vocational Training Program

    Training in web software development: Java, PHP, JavaScript and TypeScript, relational databases, API development, and web application deployment.

    Web development Java PHP TypeScript SQL

05. contact

Let's talk

I'm looking for a place to keep growing as a backend developer. And if you have an idea and need help bringing it to life, get in touch — let's shape it together.

Send email GitHub LinkedIn

zar0_31@outlook.com