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leon-lourenco/README.md

Hi, I'm Leon (:

Senior Backend Engineer · Java/Spring · Fintech & Payments · Cloud-Native Microservices

São Paulo, Brazil  ·  Remote / USD contractor preferred  ·  GMT-3


About

I have 8 years of experience developing resilient, high-availability backend solutions for contexts that demand large-scale data processing.

I'm a senior individual contributor who turns complex legacy or regulated domains into measurable delivery: legacy Java modernization (Java 6 → Java 21), payment and digital banking systems at scale, distributed systems, messaging, and production support — with English-fluent international delivery experience (T-Mobile CCPA compliance with US leadership).

Lately I've also been applying AI-assisted engineering (prompt engineering, LLM provider integrations, MCP Servers) to speed up legacy code analysis, debugging, and technical research.

  • Payments & digital banking: Digital Account, salary portability, Payment Gateways, POS integrations, PIX, Open Finance
  • Legacy modernization: Java 6 → Java 21, monoliths with 70+ modules, dependency/vulnerability remediation
  • Cloud-native backend: microservices, hexagonal architecture, Kafka/RabbitMQ, AWS/Azure/GCP, Kubernetes
  • Observability: OpenTelemetry, Micrometer, Prometheus, Grafana
  • AI-assisted engineering: LLM provider integrations, MCP Servers, A2A, prompt engineering for code analysis & debugging

Tech Stack

Languages & Frameworks

Data, Messaging & Infra

Testing & Observability


Highlights

  • Technology Consultant / Senior Software Engineer / Technical Lead across enterprise client engagements for 6+ years
  • Eliminated 5,000+ vulnerabilities in a global payment platform in my latest contract for a US-based company, some open for 6+ years
  • Improved salary-portability query performance by 80%+ and built 1,300+ unit tests at a large digital banking
  • Modernized core credit systems from COBOL/mainframe to Java microservices at one of the largest banks in Brazil
  • Reduced daily financial batch processing from 2 hours to 30 minutes (3M+ entries/day) at one of the largest insurance companies in Spain
  • Designed and engineered a microservices architecture for CCPA compliance for a leading U.S.-based telecommunications company.
  • Helped develop FullCam from the ground up, scaling it to 30,000 customers and reducing live video latency from 6 seconds to 20ms using WebRTC, while gaining my first experience as a technical lead just three years into my career.

Professional Journey

act digital Consulting × Fiserv — Senior Software Engineer (2026 – Present · Remote)

Currently modernizing Software Express, a high-criticality global payment platform. I've eliminated 5,000+ vulnerabilities — some open for over 6 years — while upgrading a 70+ module monolith from Java 1.6 to Java 21 and cutting build time from 23 minutes to 5. Along the way I onboarded 6 new partners into the platform and leaned on an AI-first engineering workflow to speed up legacy analysis and modernization planning.

TQI Consulting × PagBank — Senior Software Engineer (2025 – 2026 · Remote)

Back to digital banking, this time on PagBank's Digital Account and Terminals products. I refactored the core salary-portability queries for an 80%+ performance gain, rebuilt the domain's test suite with 1,300+ new tests, and supported a product launch that grew the customer base by 20% in five months — all while owning production support across 200+ customer tickets.

IBM Consulting — Technology Consultant / Senior Software Engineer / Technical Lead (2022 – 2025 · Remote)

Three years, four very different enterprise clients, one common thread: modernizing critical systems without breaking them.

  • T-Mobile — delivered a 15-microservice cloud structure for CCPA compliance in 10 months, working directly with US-based leadership.
  • Itaú — helped migrate core credit systems from COBOL/mainframe to Java/Kotlin microservices across 3 squads, and onboarded 15+ engineers along the way.
  • MAPFRE — cut daily financial batch processing from 2 hours to 30 minutes for 3M+ daily entries by parallelizing core Spring Batch operations.
  • Bradesco — architected enterprise integrations for contract and billing management, contributing to Open Cash Hub, an initiative projected to generate R$5 billion over 3 years.
Yapay Pagamentos Online / Vindi — Mid-Level Software Engineer (2021 – 2022 · Remote)

My first real dive into payments. I maintained SuperPay, the company's legacy gateway, and joined the New Business team building integrations across Yapay's financial ecosystem — payment and POS backend features spanning Ruby on Rails and Java EE. This is where the fintech thread of my career really started.

Fulltime Gestora de Dados — Software Developer → Backend Team Lead (2018 – 2021 · Garça, SP)

I joined right out of school and helped build FullCam, a real-time camera monitoring platform, from the ground up. Over three years I grew into the backend team lead — guiding architecture and technology decisions while onboarding 10+ engineers. We took FullCam from zero to 30,000 customers, built cloud and on-premise microservices around FFMPEG, OpenCV, WebRTC, and MQTT, and shipped a notification architecture that delivered 15M+ alerts. The proudest engineering win: reworking live-camera viewing with WebRTC and cutting display latency from 6 seconds down to 20 milliseconds.


Let's connect

I'm open to senior backend / fintech-payments engineering roles — remote, USD-denominated contractor preferred.

LinkedIn · leondeveloper1@gmail.com

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