Open to opportunities

Haessler León

@haesslerlen

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I build full-stack and mobile fintech, Web3, and e-commerce applications used at scale.

Brazil

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What I'm looking for

I'm seeking a remote Full-Stack or Mobile Developer opportunity where I can build scalable web and mobile products, contribute across frontend and backend systems, and apply my experience in fintech, Web3, AI integrations, and team leadership.

I've built production web and mobile applications for 7Net Corporation, Busi Technology Developments, TurpialDev, and Zumetrics, spanning fintech, Web3, and e-commerce. My work includes backend improvements that lifted performance by 15%, financial modules optimized by 7%, and AI-agent workflow integrations using MCP and n8n.

At Busi, I led development of three mobile applications supporting 30,000+ active users and introduced a Yarn monorepo that reduced code duplication by 40%. I've also led a five-developer team building a real-time financial dashboard for 5,000+ monthly users, delivered cross-chain transactions with a 99.8% success rate, and work across React, React Native, Node.js, Next.js, Nest.js, and native mobile tooling.

Experience

Work history, roles, and key accomplishments

Full Stack & Mobile Developer

Haessler León

Full Stack & Mobile Developer with 9+ years of experience building production-grade web and mobile applications across fintech, Web3, and e-commerce. Specializes in React, React Native, Node.js, Next.js, and Nest.js, with hands-on experience leading teams, architecting scalable backend systems, and shipping mobile apps to 30,000+ active users.