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Sergio Ballestero
Looking for a jobFounder & Principal Engineer
Senior Full-Stack Engineer (React, Next.js, NestJS, PostgreSQL) with a design background. 18+ years, building SaaS for US teams.
ParaguayFounder & Principal Engineer at Welcomy.io
About
Remote senior full-stack role with a US product team, owning features end to end in React/Next.js and NestJS or FastAPI on PostgreSQL. I design in Figma and build what I design, so I fit product-minded teams that ship often and value clear async communication. Based in Paraguay (UTC-3), good US overlap; open to long-term contract or full-time.
At Welcomy.io, I took a multi-tenant queue-management SaaS from schema to production as its sole engineer. I built its ticketing, priority handling, kiosk displays, and visitor analytics, along with AI Insights and Forecasting that can route between Claude, Gemini, and a locally hosted model.
As an independent Full-Stack Engineer, I’ve worked with US and regional product teams across proptech, VoIP, and workflow automation. At Hilagro (TransAgro), I designed and built a supplier and accounts-payable portal that automates invoice-to-purchase-order reconciliation; at BrightReps FlowEQ, I built a workflow step editor and analytics.
Earlier, I built the university intranet and student and teacher mobile apps for Universidad del Pacífico, and led development of a GPS fleet-tracking platform at Global Tracking Paraguay. Formal graphic design training informs how I work: I design interfaces in Figma and then build them.
Experience
Founder & Principal Engineer
Multi-tenant queue-management SaaS — ticketing, priority handling, kiosk displays and visitor analytics. Sole engineer across backend, frontend and infrastructure; deployed to production and recruiting its first pilot users.
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