Senior Full Stack Developer | C#.NET, React | London

Source Technology Limited; Greater London; On-site; GBP 144,000 - 176,000; Full time

Job summary

Source Technology Limited in London, United Kingdom, is seeking a Senior Full Stack Developer to build high-performance, secure digital products for Financial Services. You will work across backend services and modern web front ends, influencing architecture, delivery, and engineering standards.

You will design and implement scalable services with C#/.NET and REST APIs, build React interfaces, ensure security, and contribute to CI/CD and cloud deployments while mentoring peers.

Qualifications

• Extensive commercial experience in full stack development with C#/.NET and React.
• Strong knowledge of .NET Core, DI, asynchronous programming, and API design.
• Strong React experience including state management and modern front-end tooling.
• Solid understanding of software design principles, patterns, and clean code.
• Experience with SQL databases, ORM tooling (e.g., Entity Framework), and data modelling.
• Experience with cloud platforms (Azure and/or AWS), containerisation (Docker), and CI/CD.
• Understanding of Financial Services constraints: security, auditability, data protection, and resiliency.
• Strong communication skills and ability to work effectively in an agile environment.

Responsibilities

• Design, develop, test, and maintain scalable services using C#/.NET (ASP.NET Core) and RESTful APIs.
• Build responsive, accessible user interfaces using React, TypeScript, HTML, and CSS.
• Implement secure authentication/authorisation (e.g., OAuth2/OIDC) and follow secure coding practices.
• Optimise performance, reliability, and observability (logging, metrics, tracing).
• Work with relational databases (e.g., SQL Server) including schema design, queries, and tuning.
• Write automated tests (unit, integration, end-to-end) and participate in code reviews.
• Collaborate with product, design, and stakeholders to refine requirements and deliver iteratively.
• Contribute to CI/CD pipelines and cloud deployment practices.
• Mentor engineers and promote best practice in engineering craft and delivery.

Skills

C#/.NET

React

RESTful APIs

OAuth2/OIDC security

Azure/AWS cloud

Docker

CI/CD

SQL Server

Agile/Team collaboration

Tools

Entity Framework

Docker

Terraform

Job description

Location: London, United Kingdom

Industry: Financial Services

Salary: £160,000

Overview

We are seeking a Senior Full Stack Developer to build and enhance high-performance, secure digital products within Financial Services. You will work across backend services and modern web front ends, contributing to architecture, delivery, and continuous improvement. This is a hands-on role with strong influence over engineering standards, quality, and technical direction.

Key Responsibilities

• Design, develop, test, and maintain scalable services using C#/.NET (ASP.NET Core) and RESTful APIs.
• Build responsive, accessible user interfaces using React, TypeScript, HTML, and CSS.
• Implement secure authentication/authorisation (e.g., OAuth2/OIDC) and follow secure coding practices.
• Optimise performance, reliability, and observability (logging, metrics, tracing).
• Work with relational databases (e.g., SQL Server) including schema design, queries, and tuning.
• Write automated tests (unit, integration, end-to-end) and participate in code reviews.
• Collaborate with product, design, and stakeholders to refine requirements and deliver iteratively.
• Contribute to CI/CD pipelines and cloud deployment practices.
• Mentor engineers and promote best practice in engineering craft and delivery.

Required Skills & Experience

• Extensive commercial experience in full stack development with C#/.NET and React.
• Strong knowledge of .NET Core, dependency injection, asynchronous programming, and API design.
• Strong React experience including state management and modern front-end tooling.
• Solid understanding of software design principles, patterns, and clean code practices.
• Experience with SQL databases, ORM tooling (e.g., Entity Framework), and data modelling.
• Experience with cloud platforms (Azure and/or AWS), containerisation (Docker), and CI/CD.
• Understanding of Financial Services constraints: security, auditability, data protection, and resiliency.
• Strong communication skills and ability to work effectively in an agile environment.

Desirable

• Experience with microservices, event-driven architecture (e.g., Kafka/RabbitMQ), and distributed systems.
• Infrastructure as Code (e.g., Terraform/Bicep) and advanced monitoring/alerting practices.
• Experience building systems with low latency and high throughput requirements.

What You’ll Bring

• Ownership mindset, pragmatic decision-making, and a focus on delivering value safely.
• Commitment to engineering excellence, continuous learning, and improving team ways of working.