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Full-stack engineer shipping production SaaS end to end—React/Next.js on the front, Python/FastAPI and Node.js/NestJS on the back, and PostgreSQL/MySQL under the hood. I also run Welcomey.io, a multi-tenant queue-management SaaS I built from schema to production. I design interfaces in Figma and then build them, train formal design systems behind the scenes, and deliver automation and integrations (Stripe, HubSpot, OAuth providers, webhooks, and workflow tooling) with testing, CI/CD, Docker, and AWS deployment.…Full-stack engineer shipping production SaaS end to end—React/Next.js on the front, Python/FastAPI and Node.js/NestJS on the back, and PostgreSQL/MySQL under the hood. I also run Welcomey.io, a multi-tenant queue-management SaaS I built from schema to production. I design interfaces in Figma and then build them, train formal design systems behind the scenes, and deliver automation and integrations (Stripe, HubSpot, OAuth providers, webhooks, and workflow tooling) with testing, CI/CD, Docker, and AWS deployment.

Sergio Ballestero Luque

Front-End Developer, Full Stack Developer, Software Engineer, +3

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Full-stack engineer shipping production SaaS end to end—React/Next.js on the front, Python/FastAPI and Node.js/NestJS on the back, and PostgreSQL/MySQL under the hood. I also run Welcomey.io, a multi-tenant queue-management SaaS I built from schema to production. I design interfaces in Figma and then build them, train formal design systems behind the scenes, and deliver automation and integrations (Stripe, HubSpot, OAuth providers, webhooks, and workflow tooling) with testing, CI/CD, Docker, and AWS deployment.…Full-stack engineer shipping production SaaS end to end—React/Next.js on the front, Python/FastAPI and Node.js/NestJS on the back, and PostgreSQL/MySQL under the hood. I also run Welcomey.io, a multi-tenant queue-management SaaS I built from schema to production. I design interfaces in Figma and then build them, train formal design systems behind the scenes, and deliver automation and integrations (Stripe, HubSpot, OAuth providers, webhooks, and workflow tooling) with testing, CI/CD, Docker, and AWS deployment.

Available to hire

Full-stack engineer shipping production SaaS end to end—React/Next.js on the front, Python/FastAPI and Node.js/NestJS on the back, and PostgreSQL/MySQL under the hood. I also run Welcomey.io, a multi-tenant queue-management SaaS I built from schema to production.

I design interfaces in Figma and then build them, train formal design systems behind the scenes, and deliver automation and integrations (Stripe, HubSpot, OAuth providers, webhooks, and workflow tooling) with testing, CI/CD, Docker, and AWS deployment.

Skills

Experience Level

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Language

Spanish; Castilian

Fluent

English

Advanced

Work Experience

Founder & Principal Engineer at Welcomey.io

February 1, 2026 - Present

Multi-tenant queue-management SaaS with ticketing, priority handling, kiosk displays, and visitor analytics. Sole engineer across backend, frontend and infrastructure; deployed to production and onboarded initial pilot users. Built AI insights and forecasting behind a provider abstraction routing between Claude API, Gemini API, and a locally hosted Ollama model. Designed NestJS + TypeORM + PostgreSQL backend with JWT auth, Google and Microsoft OAuth, role-based access control, and a pg-boss job queue dispatching webhooks with retries. Built a Next.js 16 application plus an Astro landing site with English/Spanish routing. Operated the production stack with Docker, Traefik, Cloudflare WAF, health checks, caching and rate limiting; used Prometheus-style operational thinking via health checks, and managed deployments on a VPS with Cloudflare protections.

Founder & Principal Engineer at Welcome.io

February 1, 2026 - Present

Built Welcome.io, a multi-tenant queue-management SaaS for ticketing, priority handling, kiosk displays, and visitor analytics. Operated as the sole engineer across backend, frontend, and infrastructure, including production deployment and onboarding the first pilot users. Implemented AI insights and AI forecasting behind a provider abstraction layer that routes between Claude API, Gemini API, and a locally hosted Ollama model. Developed the backend using NestJS, TypeORM, PostgreSQL with JWT auth and RBAC, and an apg-boss job queue that dispatches webhooks with retries. Built the Next.js 16 application plus an Astro landing site with English/Spanish routing; ran the production stack on Hetzner via Coolify using Docker, Traefik, Cloudflare WAF, health checks, caching, and rate limiting.

Full-Stack Engineer at Universidad del Pacífico

August 1, 2021 - November 1, 2023

Designed and built the university intranet and student/teacher mobile apps, rolled out to the full active student and faculty body. Delivered the web frontend and the API with React and React Native. Shipped teacher-evaluation engine with a reusable question bank, result reporting, attendance, course enrollment, announcements with read receipts, and student account balances. Integrated Bancard online payments, the Moodle LMS, and the CRAI library system. Produced server-rendered PDF and Excel reports with charts. Released the MiSitioUP React Native app for students and teachers on the App Store and Google Play using Firebase push notifications.

Independent Full-Stack Engineer at Self-Employed

January 1, 2021 - Present

Contract long-running retainers with US and regional product teams across backend, frontend and platform work. Owned authentication and security layers in FastAPI and SQLAlchemy; built founder onboarding flows including Stripe billing and HubSpot CRM integration. Delivered member area and admin panel in Next.js with UI in MUI, with Alembic migrations validated in CI and Docker images deployed to AWS via GitHub Actions. Built workflow automation SaaS components using React + TypeScript with Redux-Saga and React Flow; implemented AWS Step Functions/Lambda handlers, Prisma migrations, PostgreSQL functions, and Firestore syncing. Contributed to Next.js PWA features like Leaflet mapping with clustering and polygon drawing, plus TipTap, Next-Intl, NextAuth and Sentry with automated tests (Jest, Playwright).

Independent Full-Stack Engineer (Self-Employed)

January 1, 2021 - February 1, 2026

Long-running contracts with US and regional product teams across backend, frontend, and platform. Shipped features including: authentication and security layers in FastAPI and SQLAlchemy; founder onboarding workflows with Stripe billing and HubSpot CRM integration; member area/admin panel in Next.js with an UI built in MUI and Storybook releases; CI and Docker images deployed to AWS via GitHub Actions. Built workflow-automation SaaS features (React + Redux-Saga, React Flow diagrams, AWS Step Functions/Lambda behind them, Prisma migrations, PostgreSQL functions, and Firestore sync). Delivered UI systems and PWA mapping features (Leaflet clustering/polygon drawing, TipTap, next-intl, NextAuth, Sentry) with Jest/Playwright automated tests. Developed business procurement portals (supplier/accounts payable) with Next.js, NestJS, PostgreSQL, and Redis using hexagonal architecture and invoice-to-purchase-order reconciliation via document-extraction bot and client ERP integration (SIMUXER). Sh

Full-Stack Developer at Global Tracking Paraguay

April 1, 2016 - January 1, 2021

Led development of a GPS fleet-tracking platform used over 1,000,000 times. Processed messages for 2,000+ vehicles every 15 seconds, including UDP server processing of hardware events and SMS commands. Built React + TypeScript frontend and custom WordPress dashboards backed by PHP, Laravel, and Node.js services. Ran servers and pipelines using Docker and GitLab CI.

Design Manager / Web Developer (earlier roles)

January 1, 2005 - January 1, 2016

Earlier roles focused on design management and web development for digital projects in Paraguay (2005–2016), including work for Unilever, Tigo and Miller Genuine Draft.

Design Manager / Web Developer

January 1, 2005 - January 1, 2016

Early roles in design management and web development for digital projects in Paraguay (2005–2016), including work for Unilever, Tigo, and Miller Genuine Draft.