Summary
Overview
Work History
Education
Skills
Websites
Certification
Languages
Timeline
Generic

William Freire

São Paulo, Sao Paulo

Summary

  • 6+ years of experience in backend engineering with Elixir, Golang & cloud-native solutions.
  • Expertise in DDD, microservices, and distributed systems.
  • Proven track record in FinTech, delivering scalable, secure, and auditable financial solutions.

Key achievements:

  • Automated receivable payments (68% faster) improving scalability and customer experience.
  • Refactored Elixir microservices to handle 2M+ daily requests (+150% scalability).
  • Reduced AWS costs by 50% with query and API optimization. - Strong collaboration with cross-functional teams, driving innovation in payments, treasury operations, and investment flows.

Overview

8
8
years of professional experience
1
1
Certification

Work History

Senior Software Engineer

Stone
01.2024 - Current
  • - Automatic Balance Yield Flow (Elixir/Golang): Implemented with the Ledger team and product stakeholders to deliver automated daily balance investments. This automation increased funding capacity and expanded financial margins.
  • - Funds Transfer Operation: Collaborated with the Corporate Treasury team to automate interbank reserve transfers. Built the integration in Elixir, replacing a manual process with a high-performance system, reducing risk and improving settlement operations.
  • - Financed Cashout: Developed real-time credit card limit transfer, creating a new revenue stream through interest and fees, while ensuring high system performance.
  • - Automated Receivables Payment Flow (Golang): Optimized settlement operations, making receivable payments 68% faster, significantly improving scalability and customer experience.

Senior Software Engineer

IZA Seguradora S.A.
10.2022 - 01.2024
  • - Refactored Elixir Microservices Architecture: Scaled request handling from 800k to 2M+ daily requests (+150%), enhancing reliability, throughput, and maintainability at scale.
  • - Reduced AWS Costs by 50%: Optimized database queries with Postgres Analyze and refactored APIs, cutting cloud infrastructure expenses in half while boosting performance.
  • - Implemented OpenTelemetry on Elixir Apps: Added custom metrics and alerts, enabling early anomaly detection and reducing incident resolution time by 71%, significantly increasing system reliability.
  • - Automated Financial Closing Process: Collaborated with the finance team to replace a manual closing with a fully automated solution, eliminating errors, stabilizing the application, and improving efficiency by 64%, ensuring accuracy and stability in financial operations.
  • - Comprehensive Automated Test Suite: Established robust testing practices to guarantee code quality, stability, and maintainability under high demand, while strengthening API integration and overall performance.

Software Engineer

Pipefy
02.2022 - 03.2023
  • - Optimized Legacy Feature in Ruby: Reduced latency by 35% by fixing N+1 queries and introducing asynchronous task processing, improving performance and scalability, and driving a 21% increase in customer acquisition.
  • - Mentored Team on Elixir Adoption: Led a 21-day onboarding program for five team members, accelerating knowledge transfer, boosting confidence in the stack, and increasing squad productivity by 40% in delivery speed.

Software Engineer

General Shopping&Outlets
05.2021 - 02.2022
  • - Implemented Daily Spending Limit Feature (Elixir, DDD): Built real-time validation for customer spending limits, increasing system reliability, strengthening risk controls, and enhancing customer protection while maintaining scalability.
  • - Expanded Test Coverage: Reached 60% coverage with unit and integration tests, reducing production bugs by 30% and improving scalability.
  • - Set Up CI/CD with GitHub Actions: Automated build, test, and deployment workflows, accelerating delivery cycles, reducing manual effort, and improving release reliability and developer productivity.

Software Engineer

CrediSIS
08.2020 - 05.2021
  • - Refactored Legacy System to Elixir: Migrated the main context of a legacy PHP system to Elixir with DDD and asynchronous processing, reducing latency by 48% and production errors by 32%, while boosting performance, maintainability, and customer retention.
  • - Improved Observability with Grafana & Prometheus: Built monitoring dashboards and alerts, enabling faster detection of production errors and reducing downtime, which increased system reliability and improved incident response.

Software Engineer

CrediSIS JCred
03.2019 - 08.2020
  • - Automated Manual Processes: Built a web application with Vue.js (frontend) and Laravel (API) to replace manual workflows, reducing operational effort, minimizing errors, and increasing process efficiency and reliability.
  • - Implemented AWS Cloud Services: Deployed infrastructure with S3, EC2, RDS, and ELB, enabling scalable storage, compute, database, and load-balancing solutions, which improved system availability, performance, and resilience to support business growth in the cloud.

Logic Programming Instructor

Prefeitura Municipal de Ji-Paraná
03.2017 - 12.2018
  • - Taught Programming Logic to Over 100 Students: Served as an instructor in a municipal project, teaching programming logic to more than 100 kids. Designed and delivered hands-on lessons that introduced core computational thinking concepts, fostering early interest in technology and problem-solving.

Education

Graduação - Engenharia de Software

Instituto Infnet
01.2024

Tecnológico - Análise e Desenvolvimento de Sistemas

Instituto Federal de Educação, Ciência e Tecnologia de Rondônia - IFRO
01.2018

Skills

  • Elixir
  • Golang
  • AWS
  • Microservices
  • Distributed Systems
  • DDD
  • PostgreSQL
  • API REST
  • Phoenix

Certification

  • Scrum Foundation Professional Certificate CertiProf
  • CLVPBFQYPY-SLZKLZJV-XHMWPRCTYYX
  • Issued 2020-06
  • Remote Work and Virtual Collaboration CertiProf
  • Issued 2021-02

Languages

English
Advanced (C1)
French
Elementary (A2)

Timeline

Senior Software Engineer

Stone
01.2024 - Current

Senior Software Engineer

IZA Seguradora S.A.
10.2022 - 01.2024

Software Engineer

Pipefy
02.2022 - 03.2023

Software Engineer

General Shopping&Outlets
05.2021 - 02.2022

Software Engineer

CrediSIS
08.2020 - 05.2021

Software Engineer

CrediSIS JCred
03.2019 - 08.2020

Logic Programming Instructor

Prefeitura Municipal de Ji-Paraná
03.2017 - 12.2018

Tecnológico - Análise e Desenvolvimento de Sistemas

Instituto Federal de Educação, Ciência e Tecnologia de Rondônia - IFRO

Graduação - Engenharia de Software

Instituto Infnet

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