Senior .NET Backend Developer

Optix is modernising a large, established Windows desktop platform into a modern web product. We are looking for a senior .NET backend developer with deep engineering experience, strong architectural judgement and a practical approach to modern development tools. This is a hands-on role with significant responsibility for backend architecture and delivery. You will design .NET services and APIs, turn complex legacy behaviour into maintainable solutions, and help improve engineering practices across the team. What you'll be doing Design and implement complex backend functionality using C# and modern .NET / ASP.NET Core. Make and communicate pragmatic architectural decisions across services, APIs, data and integrations. Modernise functionality from our established WinForms application into a maintainable service-based web architecture. Work with engineers, Product and technical stakeholders to shape solutions and clarify trade-offs. Lead by example. Use AI tools and coding agents across code exploration, design, implementation, testing, review, refactoring, documentation and migration, while retaining clear ownership of the outcome. Set a high standard for maintainability, automated testing, security, observability and pull-request review. Investigate complex technical and production issues and drive them through to resolution. What we are looking for Strong experience designing and operating production APIs and services with C#, modern .NET and ASP.NET Core. Proven architectural judgement across service boundaries, data ownership, integrations, scalability, resilience and maintainability. Experience with SQL, relational databases and safely evolving data-intensive backend systems. A strong approach to software design, dependency injection, automated testing and maintainable code. Ability to understand large or unfamiliar codebases and translate complex existing behaviour into a clear technical approach. A disciplined approach to AI-assisted development, including context management, task decomposition, security, testing, review and validation. Proven experience leading engineers through architectural or tooling change by setting direction, documenting decisions and coaching others. Strong communication and stakeholder-management skills, with the ability to explain decisions clearly and challenge constructively. Useful experience - not essential Experience using AI coding assistants or agents in day-to-day software delivery. Kubernetes and Docker experience, if in production even better. Authentication and authorisation platforms, and software handling sensitive or clinically important data. PostgreSQL, Redis, Elasticsearch or other data and caching technologies. GraphQL, including schema design and gateway patterns. Grafana, OpenTelemetry, Prometheus or equivalent observability tooling. CI/CD, production services, microservices and message-driven systems such as RabbitMQ. How we work We value engineers who own outcomes and remain hands-on with delivery. We encourage thoughtful use of modern tools, transparent validation and active sharing of effective practices. You will influence architecture, process, tooling and technical strategy while helping the wider team improve. Hours of work: 37.5 hours per week. Flexitime is available, with core hours of 10am-3pm Monday-Friday. The role is hybrid, with two days per week in our York office. What we offer Hybrid working – two days per week in our York office - with flexitime. Significant influence over backend architecture, engineering practices and technical direction. An environment that invests in modern engineering tools, experimentation and shared practices. 25 days holiday, increasing with service up to 30 days. Vitality Health, Life Assurance, pension, Cycle to Work Scheme, on-site parking and regular socials. About Optix Optix is a leading provider of business management software for UK opticians. Our platform supports complex clinical workflows and sensitive patient data alongside appointments, stock, marketing, finance, integrations and medical equipment. Its established functionality and ongoing modernisation create an environment in which engineers can materially influence the platform's future. Interview process Technical Test An initial conversation about your experience, the role and how we work. A technical discussion focused on .NET backend engineering, system design, architectural reasoning and your approach to modern development tools, including AI where relevant. Equal opportunities Optix Software Ltd is committed to equal opportunities in all aspects of our work. We are committed to treating colleagues fairly regardless of race, gender, disability, age, sexual orientation, religion or belief.