Senior Backend Developer (C#, .NET, PostgreSQL)

About the role

quinn is an app-based managed payroll and employment-administration service operating in Switzerland, Germany and the UK, handling registration, payroll, social insurance and taxes on behalf of employers. This role is fully focused on quinn ONE, the modular monolith in C#.NET 10 and PostgreSQL that powers the platform. It is a 100% full-time position in Zurich (Wiedikon), hybrid with three days a week in the office, reporting to the Lead Engineers.

Key responsibilities

• Own backend modules end to end: design, build, test and run them and the APIs they expose, from requirements to production.
• Own the PostgreSQL data model: schema design, migrations, transactions, indexing and the calculations that must be correct to the cent.
• Own the foundations: audit trail, logging, API and service versioning, and database upgrades.
• Ensure reliability and security in production: tests, observability, performance and data protection by design.
• Shape module boundaries, dependencies and the shared core versus country layers, and mentor developers in Zurich and the Armenia team.

Required profile

• Has shipped and run production systems in C# and modern .NET / ASP.NET Core, including under load.
• Knows PostgreSQL well: schema design, transactions, locking, indexing and query optimisation.
• Has designed APIs and modules with clear boundaries and manageable dependencies.
• Treats personal and financial data carefully; security is part of the design.
• Uses AI tools daily and can show where they helped and where they were wrong.
• Owns initiatives independently, raises risks early, reviews constructively and mentors willingly.
• English is the working language; German is a plus.

Required skills

• C#.NET 10, ASP.NET Core
• PostgreSQL
• API design and RESTful services

First-year expectations: set up and learn the system in the first month, deliver the audit trail within 100 days, and by month nine be the go-to person for the backend. The application asks for a CV and two short paragraphs explaining why the role and why now.