Guilherme Cassimiro

Backend .NET Developer

Building robust, scalable backend solutions with expertise in .NET technologies, microservices architecture, and modern database systems.

About Me

I'm a Software Developer focused on backend with C#/.NET, working daily with Entity Framework, Dapper and relational databases like SQL Server and PostgreSQL. I enjoy designing solutions using Clean Architecture, DDD and SOLID principles to keep systems maintainable and scalable.

Currently at Inside Sistemas, I work on system integrations, REST APIs and CI/CD automation using GitLab and Docker. My previous experience as a QA Tester — using tools like Postman, JMeter and Azure DevOps — helps me bring a strong quality mindset into the development flow.

I'm passionate about writing clean, testable code and collaborating with development, support and product teams to deliver stable and efficient solutions that actually solve business problems.

Clean Architecture

Building applications with Clean Architecture, DDD and SOLID principles

REST APIs & Integrations

Developing robust REST APIs and system integrations

Database Management

Expertise in SQL Server and PostgreSQL with Entity Framework and Dapper

Quality Assurance

Experience with manual and automated testing, CI/CD pipelines

Skills & Technologies

Frameworks & Languages

C# / .NET87%

Entity Framework85%

Dapper78%

Linq85%

Databases

SQL Server92%

PostgreSQL90%

SQL90%

Architecture & Design

Clean Architecture88%

DDD (Domain-Driven Design)85%

SOLID Principles90%

Testing & DevOps

Unit & Integration Tests85%

GitLab CI/CD80%

Docker80%

Also experienced with

REST APIsDockerGitLab CI/CDAzure DevOpsGitUnit TestingIntegration TestingPostmanJMeter

Experience & Projects

Jan 2025 - Present

Inside Sistemas

Software Developer

Backend developer working with C#/.NET, Entity Framework, Dapper and SQL Server/PostgreSQL on business-critical systems. I design and implement features using Clean Architecture and DDD, apply SOLID principles, and write unit/integration tests to keep the codebase reliable. I also work on system integrations, REST APIs and CI/CD pipelines with GitLab and Docker.

.NET FrameworkEntity FrameworkDapperSQL ServerPostgreSQLClean ArchitectureDDDSOLIDDockerGitLab CI/CD

Oct 2022 - Dec 2024

Inside Sistemas

QA Tester

Worked with manual and automated testing using Postman, JMeter, Azure DevOps, GitLab CI/CD and SQL. I followed best practices in version control and technical documentation, collaborating closely with development, support and product teams to deliver more stable releases, reduce production incidents and continuously improve quality processes.

PostmanJMeterAzure DevOpsGitLab CI/CDSQLJavaScriptSoftware Quality

Get In Touch

I'm currently available for freelance work and exciting opportunities. Let's discuss how I can help bring your project to life.

Let's work together

Whether you have a project in mind, need consultation on your backend architecture, or just want to connect, feel free to reach out. I'm always open to discussing new opportunities and collaborations.

guicassimiro443@gmail.com

Connect with me

GitHub

Check out my code