C#/.NET Performance Engineer – FinTech, Hybrid

Citi; Greater London; Hybrid; GBP 90,000 - 140,000; Full time

Benefits offered by this job

Hybrid working model (up to 2 days at‑

27 days annual leave (plus bank hols)

Discretionary annual bonus

Private Medical Care & Life Insurance

Employee Assistance Program

Pension Plan

Paid Parental Leave

Special discounts for employees

Learning and development resources

Job summary

Citi in London is seeking a highly capable software engineer to help redefine global finance through robust, high-volume applications. You will join a globally distributed development team and contribute to performance testing, debugging, and code optimization.

The role requires deep C# experience across .NET Framework 4.5.2+ and .NET 5+, plus familiarity with REST, OpenAPI, and modern testing frameworks. A proactive, collaborative mindset and strong communication are essential.

Qualifications

• Broad technical capability with specialist knowledge of .NET and C#.
• Strong algorithms, system design/architecture, design patterns and unit testing.
• Experience in large, distributed development teams with high availability systems.

Responsibilities

• Conduct performance testing and profiling to ensure robustness and scalability.
• Troubleshoot, diagnose, and resolve code issues and bottlenecks.
• Identify system enhancements using development procedures and script tools.

Skills

C# proficiency

.NET Framework 4.5.2+

.NET 5+

Performance testing

Unit testing (NUnit/xUnit/Shouldly)

Algorithms & system design

CI/CD (Git/GitLab/GitHub)

Linux

REST/OpenAPI/Swagger

Messaging (Kafka/RabbitMQ)

Python/Java/Bash

Security TLS

Tools

Git

GitLab/GitHub CI/CD

Job description

Citi in London is seeking a highly capable software engineer to help redefine global finance through robust, high-volume applications. You will join a globally distributed development team and contribute to performance testing, debugging, and code optimization.

The role requires deep C# experience across .NET Framework 4.5.2+ and .NET 5+, plus familiarity with REST, OpenAPI, and modern testing frameworks. A proactive, collaborative mindset and strong communication are essential.