Senior Backend Engineer — Remote (C#, .NET, SQL)

John Galt LLC.; Warszawa; Hybrid; PLN 260,000 - 380,000; Full time

Job summary

John Galt LLC in Warsaw, Poland is seeking a Senior Backend Developer with 8+ years of professional software development experience. You will design, build, and maintain scalable backend systems and APIs using C#, .NET and .NET Core, with strong emphasis on performance and reliability.

You will collaborate with frontend teams, contribute to architecture, optimise SQL Server databases, and ensure code quality, security, and maintainability across enterprise applications.

Qualifications

• 8+ years of professional software development experience, backend focus.
• Extensive experience with C#, Microsoft .NET, and .NET Core.
• Strong experience developing REST APIs, backend services, and business-critical applications.
• Solid knowledge of SQL Server, relational DB design, and query optimization.
• Understanding of software architecture, OOP, design patterns, and SOLID principles.
• Experience with automated testing, debugging, Git, and modern development practices.
• Ability to own complex technical projects and solve challenging problems.

Responsibilities

• Design, develop, and maintain backend services and applications using C#, .NET, and .NET Core.
• Build and maintain RESTful APIs and integrations supporting React-based applications.
• Design and optimize database structures, queries, and stored procedures using SQL Server.
• Develop scalable, secure, and maintainable software following established architecture and design principles.
• Identify and resolve complex technical issues, improve system performance, and ensure application reliability.
• Participate in technical design discussions, code reviews, testing, and continuous improvement initiatives.
• Collaborate with cross-functional teams to translate business requirements into effective technical solutions.
• Provide technical guidance and support to other developers.

Skills

C#

REST APIs

SQL Server

React

Git

SOLID principles

OOP

Testing

Tools

.NET Core

Azure

AWS

PostgreSQL

Docker

CI/CD pipelines

Node.js

React

SQL Server

Job description

John Galt LLC in Warsaw, Poland is seeking a Senior Backend Developer with 8+ years of professional software development experience. You will design, build, and maintain scalable backend systems and APIs using C#, .NET and .NET Core, with strong emphasis on performance and reliability.

You will collaborate with frontend teams, contribute to architecture, optimise SQL Server databases, and ensure code quality, security, and maintainability across enterprise applications.