Role: Java/Kotlin Developer (Backend Mobile)

Location: Hybrid, City of London, 3 days per week

Contract: 12-month contract

Industry: Financial Services

IR35 determination: Inside

Rate: up to £400 per day

Responsibilities

• Design, develop, and maintain the mobile service layer (Backend-for-Frontend) supporting large-scale mobile applications
• Deliver secure, reliable, and high-performing Server Side APIs for Real Time consumer experiences
• Write clean, maintainable code and contribute to code reviews, refactoring, and continuous improvement initiatives
• Collaborate with mobile, product, and design teams to define solutions that enhance usability and functionality
• Troubleshoot and optimize application performance for responsiveness and scalability
• Create robust unit tests and integration tests to ensure software reliability
• Manage asynchronous processing, error handling, and performance optimization in distributed systems
• Support Legacy system integrations and modernize existing codebases when required
• Follow CI/CD best practices and contribute to team development pipelines and build systems
• Actively share ideas, propose improvements, and participate in solution design discussions

Requirements (Must Have Skills)

• Proven experience building Server Side applications with strong understanding of modern Back End development practices
• Proficiency in Kotlin or related JVM languages (Java, Scala, etc.)
• Practical knowledge of RESTful and GraphQL (GQL) API design and integration
• Hands-on experience with Gradle or similar build tools
• Solid understanding of asynchronous programming, thread management, and performance optimization
• Experience working with CI/CD pipelines and automated testing frameworks
• Strong debugging and problem-solving skills with attention to system scalability and maintainability

Nice to Have Skills

• Experience designing or integrating RAML-based documentation into API workflows
• Familiarity with Legacy system modernization or integration within enterprise environments
• Understanding of cloud-native development patterns or containerized deployment workflows (eg, Docker, Kubernetes)