Jonathan Feller, Developer in Blumenau - State of Santa Catarina, Brazil
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Jonathan Feller

Verified Expert  in Engineering

Full-stack Developer

Blumenau - State of Santa Catarina, Brazil
Toptal Member Since
March 12, 2021

Jonathan is a passionate developer with 9+ years of experience, having worked with many technologies and teams of various sizes, from startups to big corporations. He started programming at a very early age and has been doing it ever since, always looking for exciting challenges to work on. Jonathan brings strategic vision and leadership to his work and is passionate about working with teams whose vision aligns with his values.


Gunar LTD
React, Next.js, Node.js, PostgreSQL, Docker, Google Cloud...
Mout'S Solues em TI
React, Node.js, Java, Spring Boot, REST, PostgreSQL, Angular, MySQL, SQL...
Senior Sistemas
Java, Spring Boot, Hibernate, Angular, PostgreSQL, Elasticsearch, InfluxDB...




Preferred Environment

React, Node.js, PostgreSQL, JavaScript, TypeScript, ECMAScript (ES6), Git, Visual Studio Code (VS Code), REST, GraphQL

The most amazing...

...thing I've ever done is lead the development of a corporate tax revenue module as a service for the whole company to use.

Work Experience

Full-stack Engineer

2020 - 2021
Gunar LTD
  • Led the discovery phase for multiple projects, talked to clients, and defined product requirements and proposals.
  • Architected and developed several applications from scratch.
  • Trained and led junior developers onboarding the team.
Technologies: React, Next.js, Node.js, PostgreSQL, Docker, Google Cloud, Amazon Web Services (AWS), Hasura, GraphQL, Infrastructure Architecture, APIs, Full-stack, Amazon DynamoDB, AWS Lambda, Serverless, Express.js

Full-stack Developer

2020 - 2020
Mout'S Solues em TI
  • Tasked with the full-stack development of several web platforms and apps from scratch.
  • Refactored existing APIs to follow RESTful best practices.
  • Developed an app in a week to track COVID-19 symptoms.
  • Improved legacy code quality with refactors and clean code principles.
Technologies: React, Node.js, Java, Spring Boot, REST, PostgreSQL, Angular, MySQL, SQL, MongoDB, Microservices, Docker, Azure, Amazon Web Services (AWS), Kanban, TypeScript, APIs, Architecture, Full-stack, Firebase, Express.js

Software Engineer

2019 - 2019
Senior Sistemas
  • Built and maintained an integration and migration tool between the legacy monolithic database and a new cloud distributed database.
  • Migrated business logic and features from legacy software to the new cloud-based ERP.
  • Led the development of a tax engine as a service, maintaining constrained response times with multi-million parameters.
Technologies: Java, Spring Boot, Hibernate, Angular, PostgreSQL, Elasticsearch, InfluxDB, REST, Jira, Docker, RabbitMQ, Kanban, HTML, CSS, TypeScript, APIs, Full-stack, Amazon Web Services (AWS)

C++ Software Developer

2015 - 2018
WK Sistemas
  • Developed from scratch and maintained the new Corporate Tax Module, rewriting code based on the legacy Delphi version.
  • Built the tax calculation procedure, bringing down the time from two minutes to three seconds.
  • Wrote a migration tool to move data from the legacy software to the new one.
  • Integrated the Corporate Tax Module with other modules.
Technologies: C, C++, Microsoft Foundation Class Library (MFC), COM, DCOM, Visual Studio 2015, Visual Studio 2017, TFS, Scrum

Software Developer

2014 - 2015
GOVERNANÇABRASIL S/A Tecnologia e Gestão em Serviços
  • Developed new features for the accounting module aimed at more efficient use of the software.
  • Tracked and fixed bugs using Mantis as a reporting tool.
  • Created and worked on several internal tools to allow developers to work more efficiently.
Technologies: Visual Basic 6 (VB6), Visual Basic, Subversion (SVN), TFS, SQL Server 2008 R2, SQL Server 2012, C#, Scrum, Visual Studio 2015, Visual Studio 2017, Mantis

Talent Panel

It is a platform to help a company choose the best talent for their trainee program, with interactive dashboards and real-time voting. I had the chance to talk to the client and understand each step of the process; everything was done on paper beforehand. I was a full-stack developer and also presented the platform and assisted in deploying it on the client's infrastructure.

jfGL - An Independent Graphics Library

I believe the best way to learn is by doing. I was really interested in computer graphics and wanted to get a deeper knowledge of this field. As a result, I've come up with an independent 3D graphics library.

I implemented vector and quaternion operations and matrix transformations.

Applied Gouraud shading and Phong shading with point and directional lighting.

Implemented scan-line rendering algorithm with back-face culling, z-buffering, and frustum clipping.

Every pixel is rendered in software; there is also a 3D editor and texture mapper developed on top of it.


You choose a word, draw, and other players must guess what you're drawing. The sooner they guess, the more points they (and you) get.

This project was fun to develop and quite simple in its essence, heavily focused on real-time data communications and network optimizations, simple UI with a real-time chat for people to guess the word and interact.


JavaScript, ECMAScript (ES6), Visual Basic 6 (VB6), C, CSS, HTML, TypeScript, Visual Basic, C++, Java, SQL, GraphQL, C#


Angular, Next.js, Spring Boot, Hibernate, Express.js


React, Node.js, Microsoft Foundation Class Library (MFC), Socket.IO


Docker, Visual Studio Code (VS Code), Visual Studio 2017, Azure, AWS Lambda, Amazon Web Services (AWS), Firebase


Full-stack, 3D Graphics, Mathematics, Infrastructure Architecture, APIs, Architecture, COM, DCOM, Serverless


Git, Visual Studio 2015, Subversion (SVN), TFS, Mantis, Jira, RabbitMQ


REST, Microservices, Scrum, Kanban


PostgreSQL, MySQL, Google Cloud, Redis, SQL Server 2008 R2, SQL Server 2012, Elasticsearch, InfluxDB, MongoDB, Hasura, Amazon DynamoDB

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