Principal C# Backend Engineer - .Net 8/9, AWS (Lambda, SQS), Agentic Workflows (Claude Code), MySQL – OUTSIDE IR35
Reporting to the Director of Engineering, this is a genuinely outstanding contract opportunity for a rockstar Principal C# Engineer to lead the development of a greenfield SaaS product. We’re looking for a ‘best of breed’, deeply senior, technically hands‑on engineer who thrives in complex problem spaces and fast-moving start-up & scale-up environments. You’ll need a genuinely Product Centric mindset and approach twinned with experience of AI‑Native Engineering and Agentic Workflow.
Skills We’re Looking For:
* Senior–Staff‑level backend engineer with deep, current expertise in C# and .NET Core 8/9, capable of architecting and leading the design of distributed REST API microservices at scale.
* Authority in AWS serverless architecture; Lambda‑first, with strong working knowledge of API Gateway, SQS, Step Functions, EventBridge and IAM, and a track record of shipping production workloads on this stack.
* Deep data expertise across Aurora RDS MySQL and DynamoDB; schema design, access patterns, indexing, query tuning, single‑table vs multi‑table trade‑offs, and pragmatic thinking around consistency, scaling and cost.
* Hands‑on experience with Claude Code and advanced agentic workflows; multi‑agent orchestration, context management, custom commands/skills and scaling AI‑assisted delivery across a team.
* Proven experience designing event‑driven systems with SQS and adjacent AWS messaging; idempotency, retries, ordering, DLQs and operational robustness.
* Strong API design sensibility; versioning, documentation, throttling, backwards compatibility and a genuine obsession with developer experience.
* A strong product brain; comfortable operating without a traditional Product Owner, partnering with BAs, making sensible trade‑offs, prioritising ruthlessly and owning the solution through to delivery.
* Excellent communication skills and comfort with ad‑hoc client interaction, able to ask the right questions, shape requirements and translate outcomes into shippable work.
* Rigorous engineering standards; Git‑based workflows, trunk‑based development, CI/CD (ideally GitHub Actions), IaC (AWS CDK or Terraform), comprehensive testing and secure‑by‑default coding.
* Technical leadership; lifting teams through pairing, mentoring, PR review and example.
* A pragmatic, outcome‑oriented mindset; comfortable with ambiguity, biased to shipping, and able to make sensible calls on scope, sequencing and technical debt.
What You’ll Own & Deliver:
* Architect, build and ship complex distributed services in C# and .NET Core 8/9, primarily serverless on AWS Lambda, setting the technical bar for the squad and delivering major feature sets end‑to‑end.
* Design robust data models and persistence patterns across Aurora RDS MySQL and DynamoDB; choosing the right store for the workload, tuning for scale, and modelling for both transactional and high‑throughput access patterns.
* Build resilient, event‑driven systems using SQS and related AWS messaging primitives; idempotency, retries, DLQs, ordering and clean service boundaries.
* Own each feature’s solution end‑to‑end; partnering with BAs on high‑level problems, then driving product thinking, scoping, trade‑offs and delivery yourself.
* Leverage Claude Code and advanced agentic workflows; orchestrating sub‑agents, managing context, running parallel workstreams and embedding AI‑native engineering patterns into everyday delivery.
* Design clean, well‑versioned, well‑documented APIs that other engineers love to consume; treating developer experience and contract stability as first‑class concerns.
* Shape architecture and technical direction with Principal Engineers; making well‑reasoned decisions on service boundaries, data design, messaging patterns, consistency guarantees and performance.
* Champion a high‑quality engineering culture; test coverage, peer review, CI/CD discipline (GitHub Actions), IaC, secure coding, observability and performance
* Mentor and up‑level engineers through pairing, PR review, architectural guidance and practical coaching on AI‑assisted development.
£875 - £900 per day. OUTSIDE IR35. 100% remote. 6 months rolling.