Senior .NET Engineer (Data Platform & AI Agents)

What you work on today shapes where you’ll be tomorrow.

Looking for your next challenge as a Senior .NET Engineer (Data Platform & AI Agents)? We may have the right opportunity for you.

At B3, we start with people and their experience. We match projects to your skills and professional growth path. Our consultants work across a wide range of industries and technologies, delivering IT projects both in Poland and internationally. This allows you to build your career in a deliberate way - not by chance.

We are part of an international organization listed on Nasdaq Stockholm, operating in 11 countries. In Poland, we operate with full autonomy. We choose our technologies, processes, and ways of working while maintaining the highest professional standards.

Join us today.

What we offer

• Work in a Scandinavian culture built on logic, trust, and open dialogue.

• Health and sports benefits tailored to your needs.

• Speed Coaching - short sessions designed to provide new perspectives and solutions.

• Sports training, an internal team, and opportunities to take part in competitions.

Key areas of the role:

• Designing and developing data platform services in a multi-tenant SaaS architecture (data ingestion, schema management, snapshots, calculated fields, exports) using .NET, Entity Framework/Dapper and PostgreSQL

• Building tools that dynamically generate performant queries, tailored to each customer's unique data model - with a focus on performance and cost optimization (bulk ingestion, streaming, complex SQL queries)

• Developing agentic tooling supporting the team's work (custom skills and sub-agents, MCP tools exposing internal APIs) and collaborating with Data Platform, Analytics, Support and Product teams to ensure the quality of AI-generated code

What you need to join us:

Must have:

• Senior-level, 5+ year experience building production, performant and scalable backend services in .NET/C# (preferably in a multi-tenant SaaS environments)

• Strong SQL and PostgreSQL skills (schema design, query optimization)

• Performance/memory awareness (streaming vs. buffering, profiling, load testing), along with understanding of .NET architecture

• Daily experience working with AI/agents (e.g. Claude Code) - turning requirements into agent-executable specifications and critically reviewing outcomes (hallucinations, architectural drift, security issues)

• Testing and quality discipline (unit/integration tests) and excellent written communication (architecture documentation, specifications, PR descriptions)

• Fluent English (C1)

• Eligibility to work in Poland (citizenship, residence card, visa, etc.)

Nice to have:

• Microsoft Fabric or Spark

• MCP servers or exposing internal APIs as agent-callable tools

• LLM evaluation (eval suites, behavioral test design, benchmarking agent workflows)