Senior .NET Backend Developer (AI)

Quick Facts

Senior .NET Backend Developer (AI) — Freelance contract for 6 months, with possibility to extend.

Description

Lead the development of AI capabilities in a SaaS platform that provides procedures and practice guidance for public sector and social care organizations in the UK. Build production-grade RAG and AI search on Azure (Azure OpenAI, Azure AI Search, Semantic Kernel), integrate with a headless CMS (Squidex), and ensure quality, safety, and compliance in a regulated domain. Combine hands-on development with technical leadership and knowledge transfer so the client team can run what you build.

Responsibilities

• Agree AI architecture and roadmap with the Head of Product and Engineering Manager.
• Lead design and code reviews and document AI technical decisions as lightweight decision records.
• Mentor C# developers in AI engineering practice, prompt design, and evaluation.
• Make build-vs-buy recommendations for models, services, and tooling (including cost and risk).
• Build RAG-based grounded search with citations to source procedures.
• Implement hybrid search (keyword + vector) and relevance tuning, including content scoping per authority.
• Deliver AI features such as summarisation, “what’s changed” highlighting, and AI-assisted authoring; integrate with Squidex and build ingestion pipelines to keep indexes synced with published content.
• Design and run AI workloads on Azure using infrastructure as code and CI/CD with the SRE team.
• Monitor latency, quality, and cost with Application Insights and Azure Monitor; keep token spend predictable.
• Create evaluation sets and automated checks for accuracy, grounding, and regressions before releases.
• Add guardrails against hallucination, prompt injection, and cross-tenant content leakage.
• Ensure compliance with UK GDPR, data residency, and accessibility (WCAG 2.2 AA).
• Move AI features through Beta and GA quality gates with clear evidence.
• Keep architecture, runbooks, and decision records current and pair with client engineers for in-house ownership.

Requirements

• 7+ years of professional C#/.NET development, including recent .NET (8 or later), ASP.NET Core, and REST API design.
• Hands-on production experience shipping LLM-based features (ideally RAG or AI search), not just prototypes.
• Knowledge of embeddings, vector search, chunking strategies, and prompt design and how they affect answer quality.
• Strong Azure experience with Azure OpenAI and/or Azure AI Search, plus core services (App Service or AKS, Functions, Storage, Key Vault).
• Experience using AI development tools (e.g., Claude Code, Codex).
• Automated testing, CI/CD, observability, and infrastructure as code using Bicep or Terraform.
• Practical approach to data protection and security for sensitive information.
• Can clearly explain technical trade-offs to product, compliance, and customer-facing stakeholders.
• English level C1 or higher.

Benefits

• Freelance contract for 6 months with potential extension.