Senior .NET Engineer (Data Platform & AI Agents)

b3consultingpoland; Kraków; Hybrid; PLN 180,000 - 240,000; Full time

Job summary

B3 Consulting Poland is seeking a Senior .NET Engineer to design and build data platform services for a multi-tenant SaaS in Kraków. You will work with .NET, PostgreSQL and related tech to deliver scalable backend solutions.

You will collaborate with Data Platform, Analytics, Support and Product teams to refine requirements, ensure code quality for AI-generated tooling, and contribute to high-performance systems in a dynamic, international setting.

Qualifications

• Senior-level backend experience with .NET/C# in multi-tenant SaaS environments.
• Strong SQL/PostgreSQL design and query optimization.
• Performance/memory-aware design and .NET architecture knowledge.
• Experience with AI/agents and evaluating agent outputs.
• Testing/quality discipline: unit/integration tests; good documentation.
• Fluent English (C1).
• Eligibility to work in Poland.

Responsibilities

• Design data platform services in a multi-tenant SaaS using .NET, EF/Dapper and PostgreSQL.
• Build tools to generate performant queries tailored to customer data models, optimizing performance and cost.
• Develop agentic tooling and collaborate with Data Platform, Analytics, Support and Product teams to ensure AI-generated code quality.

Skills

Backend .NET/C#

SQL / PostgreSQL

Performance optimization

AI/agents

Testing & docs

English (C1)

Poland work eligibility

Job description

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)