Senior .NET/React Backend Engineer (AI-Driven)

Instinctools; Polska; Hybrid; PLN 180,000 - 240,000; Full time

Benefits offered by this job

Business-critical work

Legacy + modern tech

Technical autonomy

Pragmatic AI adoption

Sustainable pace

International collaboration

Professional development

Job summary

instinctools is seeking a Senior Fullstack (.NET + React) Developer to join a long-term project for a multinational tech company in the wireless sector. You will design, implement, and modernize backend services using C#/.NET across modern and legacy platforms, while contributing to frontend tasks with React when needed.

The role emphasizes production-quality engineering, architectural involvement, and AI-assisted development with occasional onsite sessions in Munich 1–2 times per year.

Qualifications

• 5+ years of professional experience in backend development with C#/.NET in enterprise production environments.
• Strong hands-on experience with modern .NET and .NET Framework.
• Practical experience with .NET 8 and Microsoft SQL Server.
• Experience working with legacy .NET applications, particularly .NET Framework 4.8, ASP.NET Web Forms, and IIS.
• Strong SQL Server skills, including database schema design, query optimization, and performance tuning.
• Solid experience designing and implementing REST APIs, including contract-first API development.
• Working proficiency with React and the ability to contribute to frontend tasks when required.
• Hands-on use of AI-assisted development tools and a willingness to apply them across backend, frontend, and testing activities.

Responsibilities

• Design, develop, and maintain backend services and APIs using C# and .NET.
• Work with both modern .NET 8 and legacy .NET Framework 4.8 applications, including ASP.NET Web Forms hosted on IIS.
• Design, implement, and optimize SQL Server schemas, queries, and data access, with a focus on performance and reliability.
• Own REST API design and contract-first implementation, collaborating with the team’s system architect and other engineers.
• Use AI-assisted development tools to implement features, investigate issues, generate or improve tests, and support frontend development.
• Review, test, and validate AI-generated code rather than relying on generated output without verification.
• Take ownership of tasks beyond your primary backend specialization when this helps the team deliver a complete solution.
• Contribute to frontend changes in React when needed, using AI tools to support implementation and testing.
• Participate in architectural discussions and contribute to the gradual modernization of existing systems.
• Coordinate technical dependencies across teams, share knowledge, and support the safe delivery of changes to production.
• Participate in sprint planning, PI planning, defect triage, and other team delivery activities.
• Collaborate with a distributed international team and participate in periodic onsite sessions in Munich, approximately 1–2 times per year.

Skills

C#

React

ASP.NET

SQL Server

REST APIs

AI-assisted development

Tools

IIS

Azure DevOps

Docker

Job description

instinctools is seeking a Senior Fullstack (.NET + React) Developer to join a long-term project for a multinational tech company in the wireless sector. You will design, implement, and modernize backend services using C#/.NET across modern and legacy platforms, while contributing to frontend tasks with React when needed.

The role emphasizes production-quality engineering, architectural involvement, and AI-assisted development with occasional onsite sessions in Munich 1–2 times per year.