Senior Software Engineer (Contract)

Role: Senior Software Engineer (Contract)Location: Fully Remote (UK)Day Rate: £400-£450 per day (Inside IR35)Contract Length: 6 months (Possible Extension)

We’re looking for an experienced Senior Software Engineer (Contract) to join on an interim basis and drive performance improvements across our applications and infrastructure. You’ll be responsible for identifying bottlenecks, putting the right telemetry in place, and helping our teams deliver a faster, more reliable experience for customers at scale.

Key Must Have Skills:

• .NET (C#),
• DOM performance
• JavaScript
• MS SQL Server, query optimisation, and indexing strategies
• K6, Playwright, AppInsights
• Azure DevOps - CI/CD pipelines and observability tooling

What you’ll be doing

• Front-end performance: Investigate and optimise browser behaviour, including JavaScript execution, rendering, and DOM interactions.
• Backend performance: Analyse .NET applications for efficiency, memory usage, and concurrency, implementing improvements where needed.
• Database tuning: Optimise SQL queries, indexes, and overall database performance.
• Instrumentation & monitoring: Expand and refine telemetry across the stack using tools such as AppInsights, K6, and Playwright.
• Collaboration: Partner with engineers, testers, and product teams to prioritise performance initiatives, share best practices, and influence long-term improvements.
• Load testing: Support the design and execution of realistic load/performance scenarios to uncover weaknesses and recommend fixes.

What we’re looking for

• Strong background in performance engineering across browser, server, and database layers.
• Hands-on expertise with:
• JavaScript profiling and browser internals.
• .NET (C#), async programming, concurrency, and memory management.
• SQL Server query tuning and indexing.
• Familiarity with modern observability and testing tools (e.g. K6, Playwright, AppInsights, Azure DevOps).
• Good knowledge of CI/CD practices and performance instrumentation.
• Clear communicator, able to turn complex technical findings into actionable recommendations.
• Independent, proactive, and delivery-focused.

Nice to have

• Experience working with Vue.js or other modern front-end frameworks.