C# .NET Core Developer - Hybrid - Banking

Tier 1 Bank - .NET CORE / React / Banking / Architecture

Role - C# Developer / .NET Core Duration - 6 months with very likely extensionLocation - Hybrid / Canary Wharf - 3 days per week in a Canary Wharf office

Rate - £415 p/d inside IR35
Tech Stack

• C#
• .NET Core
• SQL / Oracle
• React / Typescript

Role

• Deliver, modernise, and support business-critical applications, frameworks and services across our stack (.NET Framework/.NET Core, HTML/CSS/TypeScript/React, Python, SQL Server, Oracle). The role focuses on refactoring legacy systems to reduce technical debt, improve reliability and performance, and embed modern security patterns across the service estate.

Tasks

• Design, build, and maintain server-side and client-side software using .NET (Framework/Core), React/TypeScript, Python, and relational databases (SQL Server, Oracle); contribute to API and UI development, data access layers, and integration points.
• Refactor and modernise legacy codebases: modularisation, dependency updates, performance tuning, improved observability, and raising automated test coverage within CI/CD.
• Embed modern security patterns and controls across web services: strong authentication/authorization (e.g., OAuth2/OpenID Connect), token-based access, secure session management, least privilege/role-based access, mTLS/TLS hardening, secure secrets handling, input validation and output encoding (OWASP), dependency vulnerability remediation, and policy enforcement via gateways.
• Participate in greenfield projects: design and implement new applications and services, ensuring scalability, maintainability, and security from inception.
• Database engineering: optimise queries and schemas, implement safe migrations, and tune performance for SQL Server and Oracle workloads.
• Quality and release discipline: write and maintain unit/integration tests, participate in code reviews, and adhere to Change Management Control procedures for approvals and production updates.
• Operations and collaboration: investigate incidents, diagnose production issues, contribute to runbooks and documentation;

GCS is acting as an Employment Business in relation to this vacancy.