Senior .NET Developer (FIX & Identity)

KARIER; Warszawa; Hybrid; PLN 260,000 - 380,000; Full time

Job summary

KARIER in Warsaw, Poland, seeks a strong backend engineer with fintech focus to help design scalable microservices in .NET, MongoDB, Redis, RabbitMQ, Pulsar, and Elasticsearch. You will collaborate with a 7-person engineering team and contribute to API design and distributed systems.

The ideal candidate has 5+ years of backend development, deep C# / .NET experience, and hands-on knowledge of FIX Protocol, quantitative finance libraries like QuantLib, OAuth2/OIDC, and NoSQL databases.

Qualifications

• 5+ years of backend development experience.
• Strong C#/.NET (Java may be considered).
• Experience building APIs and distributed messaging systems.
• Experience with event-driven architectures.
• FIX Protocol experience in capital markets/electronic trading.
• Experience with financial calculations, pricing engines, or quantitative models.
• Hands-on experience with QuantLib or similar libraries.
• OAuth2, OpenID Connect, IdentityServer or similar authentication frameworks.

Skills

C# / .NET

APIs

Event-driven

FIX Protocol

QuantLib

OAuth2 OIDC

MongoDB

Capital markets

Tools

MongoDB

Job description

We are looking for Strong backend engineer with experience in the FinTech domain, working on a microservices and event-driven architecture based on .NET, MongoDB, Redis, RabbitMQ (MassTransit), Pulsar, and Elasticsearch. Experienced in designing scalable distributed systems and collaborating within a 7-person engineering team. Additionally exposed to React development.

Critical requirements

• 5+ years of backend development experience
• Strong C#/.NET (Java may be considered)
• Experience building and designing APIs
• Distributed messaging systems and event-driven architectures
• FIX Protocol experience in a capital markets / electronic trading environment
• Experience with financial calculations, pricing engines, or quantitative models
• Hands-on experience with QuantLib (or similar quantitative finance libraries)
• OAuth2, OpenID Connect, IdentityServer or similar authentication frameworks
• MongoDB or other NoSQL databases
• Experience in capital markets, fintech, trading platforms, fixed income, securities pricing