> Markdown version of [/jobs/ext/1492602-senior-software-engineer](https://www.wearedevelopers.com/jobs/ext/1492602-senior-software-engineer). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md). --- # Senior Software Engineer - **Company:** Shieldpay - **Location:** London, UK - **Experience:** Expert - **Contract:** Permanent contract - **Skills:** ASP.NET, JavaScript (Programming Language), .NET Framework, Application Programming Interfaces (APIs), Artificial Intelligence, Business Logic, ASP.NET MVC Framework, C Sharp (Programming Language), Databases, Extract Transform Load (ETL), Dependency Injection, Entity Framework, JQuery, Microsoft SQL Server, Systems Development Life Cycle, SQL Stored Procedures, SQL Databases, Data Streaming, TypeScript, Data Logging, Backend, Amazon Simple Queue Service (SQS), Code Restructuring, Web Api, Microservices - **Published:** July 30, 2026 - **Apply:** https://uk.indeed.com/viewjob?jk=5178d62cca5d5df3 ## About the Role * Senior-level, hands-on experience in modern .NET (.NET 6+) paired with deep, comfortable familiarity with legacy .NET Framework 4.8 (ASP.NET MVC 5, WebAPI 2, Entity Framework 6). We need someone who respects the legacy code and is happy working in it today. * High proficiency in reading, understanding, and safely refactoring complex, stored-procedure-heavy database logic. * Working proficiency in JavaScript/TypeScript. You'll be interacting with both jQuery on the legacy .NET front end and modern TypeScript microservices on our sister platform. * A strong "legacy technology" instinct over a "rewrite everything" approach. You favour stability, predictability, and incremental progress over shiny trends. * Experience or comfort with golden-master testing, diffing, and shadow verification to mathematically/logically prove equivalence to legacy outputs. * The ability to hold two disparate architectures in your head at once and reason through their edge cases, data flows, and coupling points. Nice-to-Haves * Hands-on experience with AWS Lambda, SQS, SNS, and RDS. * Comfort operating alongside an in-house AI-agent orchestrator that supports and automates parts of our SDLC. ## Description We are seeking a Senior Software Engineer who thrives on untangling complex systems and modernising core infrastructure without breaking production. This is an exciting opportunity to modernise core C#/SQL systems! Extract legacy business logic, build clean services, and verify changes in shadow mode with zero downtime to revenue flows. * Extract business rules scattered across C#, embedded JavaScript and undocumented SQL stored procedures into a clean, tested, dependency-free rules assemblies. * Build new services cleanly. with proper Dependency Injection (DI), robust authentication / authorization, structured logging, and full observability. * Work fluently across both legacy .NET Framework 4.8 (ASP.NET MVC5, WebAPI 2, EF6) and modern .NET, as both will coexist for the whole transition period. * Navigate across the multiple existing systems such as the API façade, the ETL pipeline, the SNS/SQS event bus, since neither system is self-sufficient and most real bugs live in the coupling, not one side. * Deploy changes using shadow-mode verification (compute, log, and compare against legacy outcomes without writing) until equivalence is rigorously proven. * Refactor and optimise heavy SQL Server stored procedures and backend logic with total precision ensuring client-money correctness is never compromised. ## Related Videos - [WeAreDevelopers LIVE - the weekly developer show with Chris Heilmann and Daniel Cranney](https://www.wearedevelopers.com/videos/1309-wearedevelopers-live-the-weekly-developer-show-with-chris-heilmann-and-daniel-cranney) - [Web APIs you might not know about](https://www.wearedevelopers.com/videos/281-web-apis-you-might-not-know-about) - [Developing the Backend with Stefan Lingler, CTO at Shpock](https://www.wearedevelopers.com/videos/100360-developing-the-backend-with-stefan-lingler-cto-at-shpock) - [Migrating half a million users to a new payment service provider](https://www.wearedevelopers.com/videos/730-migrating-half-a-million-users-to-a-new-payment-service-provider) - [Meet Your New BFF: Backend to Frontend without the Duct Tape](https://www.wearedevelopers.com/videos/682-meet-your-new-bff-backend-to-frontend-without-the-duct-tape) - [Meta Harnesses: What the JS Framework Wars Teach Us About What Is Next for AI Agents](https://www.wearedevelopers.com/videos/100353-meta-harnesses-what-the-js-framework-wars-teach-us-about-what-is-next-for-ai-agents) ## Related Articles - [Fullstack Developer Salary UK](https://www.wearedevelopers.com/magazine/251-fullstack-developer-salary-uk) - [Software Engineer Salary London](https://www.wearedevelopers.com/magazine/252-software-engineer-salary-london) - [Software Engineer Salary in The UK](https://www.wearedevelopers.com/magazine/231-software-engineer-salary-in-the-uk) - [Dev Digest 121 - AI goes offline](https://www.wearedevelopers.com/magazine/456-dev-digest-121-ai-goes-offline) - [Frontend Developer Salary in The UK](https://www.wearedevelopers.com/magazine/233-frontend-developer-salary-in-the-uk) - [Dev Digest 120 - Apple and peers](https://www.wearedevelopers.com/magazine/455-dev-digest-120-apple-and-peers)