Senior / Middle .NET Developer (E-commerce Marketplace)

Sigma Software; Warszawa; On-site; PLN 180,000 - 260,000; Full time

Job summary

Sigma Software in Warszawa is hiring a Senior/Middle .NET Developer for a large-scale E-commerce Marketplace. You will work on back-end development, integration, and scalability within an international team, contributing to a high-load ecosystem.

You will design and implement robust features, participate in the full development lifecycle, and help ensure performance, reliability, and security across services and databases.

Qualifications

• 4+ years of commercial software development with .NET/C#.
• Familiarity with .NET Framework 4.8 and OO design.
• Experience with MSMQ and WCF or similar techs.
• Strong SQL Server knowledge and T-SQL skills.
• Experience with distributed caching (NCache or similar).
• Understanding of distributed systems and event-driven architecture.
• Experience with unit, integration, and performance testing.
• English level at least Upper-Intermediate.

Responsibilities

• Design, develop, and maintain robust backend solutions in .NET.
• Own features from analysis to production deployment.
• Build scalable, secure, and well-tested code.
• Support and optimize distributed messaging and services.
• Collaborate with cross-functional teams across borders.
• Contribute to monitoring, troubleshooting, and performance tuning.

Skills

.NET/C#

MSMQ/WCF

SQL Server

Distributed caching

Distributed systems

Unit/integration testing

English (upper-intermediate)

Tools

NCache

Job description

Senior / Middle .NET Developer (E-commerce Marketplace)

• Full-time

Join a team building a large-scale marketplace platform used by millions of customers worldwide. We are looking for a Middle/Senior .NET Developer with strong expertise in distributed systems, integrations, and scalable Back-end development to contribute to the evolution of a modern E-commerce ecosystem.

In this role, you will work with complex enterprise systems, support the integration of a new e-commerce platform into the main ecosystem, and help improve the platform’s scalability, reliability, and performance. You will collaborate with cross-functional international teams and participate in the full software development lifecycle.

CUSTOMER
Our Customer is a leading international marketplace specializing in pet products, operating a large-scale digital commerce ecosystem with millions of users and extensive product catalogs. The company continuously invests in scalable technology solutions and reliable operational systems to deliver seamless online shopping experiences and support substantial transaction volumes across its marketplace services.

PROJECT

The project focuses on the development and optimization of a high-load e-commerce marketplace platform supporting catalogs, pricing, inventory, suppliers, and operational services. The position is within a newly formed team responsible for integrating a platform into the main ecosystem.

• Design, develop, and maintain robust backend solutions using .NET Framework 4.8 and C#


• Take ownership of features throughout the full development lifecycle, from requirements analysis to production deployment


• Develop clean, maintainable, scalable, and well-tested code following engineering best practices


• Support, optimize, and troubleshoot distributed messaging and service-oriented systems built with MSMQ and WCF


• Design and optimize SQL Server database structures, queries, indexes, and stored procedures


• Implement and maintain distributed caching solutions using NCache or similar technologies


• Participate in architectural discussions focused on scalability, reliability, and system performance


• Collaborate closely with developers, QA engineers, DevOps specialists, and product stakeholders


• Contribute to system monitoring, troubleshooting, and production issue resolution


• Ensure high standards of application performance, security, and maintainability




• 4+ years of commercial software development experience with .NET and C#


• Familiarity with .NET Framework 4.8


• Solid understanding of OOP principles, system design, and software architecture


• Hands-on experience with MSMQ and WCF or similar technologies


• Good SQL Server knowledge including relational database design, query optimization, indexing, and T-SQL


• Experience working with distributed caching solutions such as NCache or similar tools


• Understanding of distributed systems and event-driven architecture principles


• Experience with unit, integration, and performance testing


• Familiarity with non-functional requirements including scalability, security, high availability, and performance optimization


• At least Upper-Intermediate English level