Senior Backend Engineer - APIs, Reliability & Production

Addition; United Kingdom; On-site; GBP 80,000 - 110,000; Full time

Job summary

Addition UK is seeking a Senior Developer to own production systems, build robust APIs, and help scale a well-established SaaS platform used by thousands of customers globally. You will thrive on solving hard problems, balancing engineering excellence with delivery, and mentoring teammates in a fast-paced environment.

Expect to work on distributed services, cloud-native deployments, and third-party integrations while improving reliability, observability, and performance.

Qualifications

• Designed and maintained APIs used by customers or internal teams.
• Strong backend development experience, preferably with C# (Also open to Java or Go).
• 4-6 years experience, with at least 3+ years at one company, ideally SaaS/platform/scaleup.
• Supported systems in production and dealt with incidents when things didn’t go to plan.
• Worked with cloud-native applications or managed infrastructure environments.
• Integrated with external platforms and navigated the challenges that come with them.
• Fixed bugs you didn’t create and improved codebases you didn’t originally write.
• Learned how to balance ideal solutions with commercial realities Designed and maintained APIs used by customers or internal teams.

Responsibilities

• Building and improving APIs that support critical platform functionality
• Investigating production issues and tracing problems across distributed systems
• Working with product and engineering teams to design scalable solutions
• Improving reliability, observability and performance across existing services
• Reviewing code, sharing knowledge and helping raise engineering standards across the team
• Tackling real-world challenges around third-party integrations, data consistency and system resilience
• Debugging complex issues, from flaky dependencies to partial failures, ensuring system reliability

Skills

Backend development

C#

Java

Go

Distributed systems

Cloud-native

Production systems management

API design

Job description

Addition UK is seeking a Senior Developer to own production systems, build robust APIs, and help scale a well-established SaaS platform used by thousands of customers globally. You will thrive on solving hard problems, balancing engineering excellence with delivery, and mentoring teammates in a fast-paced environment.

Expect to work on distributed services, cloud-native deployments, and third-party integrations while improving reliability, observability, and performance.