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I am an experienced Senior Software Engineer specializing in full-stack development with a strong focus on .NET, microservices, and modern front-end frameworks. I enjoy building scalable, efficient, and user-friendly software solutions that improve business operations. I have a passion for mentorship and team leadership, helping junior developers grow while optimizing performance in enterprise applications. I thrive on collaborating with product owners and stakeholders to deliver high-quality results that meet evolving business needs.…I am an experienced Senior Software Engineer specializing in full-stack development with a strong focus on .NET, microservices, and modern front-end frameworks. I enjoy building scalable, efficient, and user-friendly software solutions that improve business operations. I have a passion for mentorship and team leadership, helping junior developers grow while optimizing performance in enterprise applications. I thrive on collaborating with product owners and stakeholders to deliver high-quality results that meet evolving business needs.

Karol Piotr Koniewicz

Full Stack Developer, Developer, Web Developer, +1

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I am an experienced Senior Software Engineer specializing in full-stack development with a strong focus on .NET, microservices, and modern front-end frameworks. I enjoy building scalable, efficient, and user-friendly software solutions that improve business operations. I have a passion for mentorship and team leadership, helping junior developers grow while optimizing performance in enterprise applications. I thrive on collaborating with product owners and stakeholders to deliver high-quality results that meet evolving business needs.…I am an experienced Senior Software Engineer specializing in full-stack development with a strong focus on .NET, microservices, and modern front-end frameworks. I enjoy building scalable, efficient, and user-friendly software solutions that improve business operations. I have a passion for mentorship and team leadership, helping junior developers grow while optimizing performance in enterprise applications. I thrive on collaborating with product owners and stakeholders to deliver high-quality results that meet evolving business needs.

Available to hire

I am an experienced Senior Software Engineer specializing in full-stack development with a strong focus on .NET, microservices, and modern front-end frameworks. I enjoy building scalable, efficient, and user-friendly software solutions that improve business operations.

I have a passion for mentorship and team leadership, helping junior developers grow while optimizing performance in enterprise applications. I thrive on collaborating with product owners and stakeholders to deliver high-quality results that meet evolving business needs.

Skills

Experience Level

Expert

Expert

Expert

Expert

Expert

Intermediate

Intermediate

Intermediate

Language

Greek, Modern

Fluent

Polish

Fluent

English

Advanced

Work Experience

Full Stack Software Engineer (Freelancer) at CUSTOMEDIALABS PA, USA

October 31, 2024 - July 25, 2025

Designed and developed a Blazor-based restaurant management system for a global fast-food franchise, featuring real-time data synchronization, an intuitive UI, and improved operational workflows. Developed the entire backend system ensuring scalability, security, efficiency, and error handling using Clean architecture, CQRS, and Mediator. Optimized API performance reducing response times by 80% and enhanced security with authentication, authorization, and memory caching (OAuth, Redis). Collaborated closely with product owners and stakeholders to define requirements and deliver high-quality software.

Senior Software Engineer at AUSTRIACARD ATH,GR

May 1, 2023 - Present

Optimized application performance through multi-threading and concurrent programming, improving efficiency. Developed and maintained RESTful APIs for seamless data exchange with external systems. Built custom solutions for major clients including PPC, Vodafone, Gov, Fraport, NBG, and IASO Group. Mentored junior developers. Implemented health checks using Next.js and .NET Core 9, improving monitoring and reliability. Developed multiple client integrations using stateless services such as Azure Functions for scalability and maintainability.

Software Engineer at Viva Wallet ATH,GR

May 31, 2023 - July 25, 2025

Enhanced the sales portal and CRM system with React and .NET Core to meet evolving business needs. Integrated third-party APIs to expand system capabilities. Developed secure and compliant financial software ensuring data integrity and regulatory adherence. Led end-to-end development of financial products covering frontend and backend using Dynamics CRM 365 and .NET Core. Designed and implemented multiple worker services using Hangfire for database projections optimizing data processing for over 500M+ records.

Software Engineer (Freelancer) at Telepost Systems ATH,GR

April 30, 2022 - July 25, 2025

Contributed to development of main control software for a pneumatic tube transport system using C++ (Wx, Cmake). Assisted in building a Windows-based GUI application for system monitoring and user interaction. Helped refine a proprietary C++ communication protocol enhancing hardware-software integration.

Software Engineer at Prosvasis Softone SA ATH,GR

January 31, 2022 - July 25, 2025

Developed a real-time CRM application using ASP.NET MVC and built an internal CRM tool with .NET Core to enhance functionality. Contributed to development and maintenance of the main product using VB.NET and .NET Framework.