Senior Software Engineer – Agentic Engineering x4

RedRock Resourcing; Reading; On-site; GBP 80,000 - 120,000; Full time

Job summary

Agentic Engineering in the UK seeks a Senior Software Engineer to modernise legacy systems using AI-driven approaches. You’ll operate at the intersection of software engineering, architecture and AI tooling to design the engineering harness and guardrails that enable safe, rapid delivery.

Bring a strong C#/.NET foundation and experience with large or legacy codebases. You’ll refactor, build AI-enabled tooling, and establish testing and evaluation frameworks to balance speed with quality.

Qualifications

• Strong software engineering foundation
• Experience with large/legacy codebases
• Exposure to AI-assisted software engineering

Responsibilities

• Use AI coding agents to investigate, refactor and modernise legacy codebases
• Design the engineering harness that gives AI agents context, rules and constraints
• Build repository-level instructions, agent skills, prompts and dynamic context
• Work with tools like Claude Code, MCP and other agentic development tools
• Establish automated testing and AI evaluation frameworks (evals) to balance speed and quality
• Build guardrails, sandboxes and CI/CD controls around AI-driven development

Skills

C#/.NET

Software architecture

AI tooling

Code refactoring

Legacy systems

Tools

Claude Code

GitHub Copilot

Codex

MCP

Job description

Senior Software Engineer - Agentic Engineering x4

Using AI and agentic engineering to modernise complex legacy software, and fundamentally change how engineering teams build software.

This isn't a traditional software engineering role. You won't simply be picking up tickets, writing code and moving onto the next sprint. You'll be working at the intersection of software engineering, architecture, AI, developer experience and legacy modernisation, helping to design the systems, standards and guardrails that allow engineers to deliver better software safely.

What will you actually be doing?

You’ll be hands-on with some seriously complex legacy technology, using modern AI tooling and engineering practices to tackle technical debt that has often been difficult to address through traditional approaches.

• Use AI coding agents to investigate, refactor and modernise legacy codebases
• Design the "engineering harness" that gives AI agents the right context, rules and constraints to work effectively
• Build repository-level instructions, agent skills, prompts and dynamic context
• Work with technologies such as Claude Code, MCP and other agentic development tools
• Establish automated testing and AI evaluation frameworks (evals) to make sure speed doesn't come at the expense of quality
• Build guardrails, sandboxes and CI/CD controls around AI-driven development

What background are we looking for?

We're looking for someone who has built a seriously strong software engineering foundation.

You’ll ideally have deep experience in C#/.NET, alongside experience working with large, complex or legacy systems.

You might have worked with:

We're particularly interested if you've also been working with:

• Claude Code, Cursor, GitHub Copilot, Codex or similar coding agents
• Agentic development or AI-assisted software engineering
• Automated testing, evals and quality frameworks
• Legacy modernisation, major refactoring or framework migrations

You’ll be joining during a major transformation across Technology, with significant investment in:

• Public cloud migration
• AI-enabled software engineering