Senior Software Engineer – Agentic Engineering x4

RedRock Resourcing; Reading; On-site; GBP 70,000 - 100,000; Full time

Job summary

RedRock Resourcing is seeking a Senior Software Engineer to work at the intersection of software engineering, AI, and legacy modernisation in Reading, UK. You will tackle complex legacy technology with AI tooling and define guardrails for safe AI-driven development.

The role focuses on building the AI-enabled engineering harness, refactoring critical systems and driving automated testing and evals to balance speed with quality.

Qualifications

• Strong software engineering foundation.
• Deep experience with C#/.NET and legacy systems.
• Experience using AI tooling for coding tasks.
• Familiarity with automated testing and evals.

Responsibilities

• Use AI coding agents to investigate, refactor and modernise legacy codebases.
• Design the engineering harness providing context, rules and constraints for AI agents.
• Build repository-level instructions, agent skills, prompts and context.
• Work with Claude Code, Cursor, GitHub Copilot, Codex and related tools.
• Establish automated testing and AI evaluation frameworks to safeguard quality.
• Create guardrails, sandboxes and CI/CD controls around AI‑driven development.

Skills

C# / .NET

Legacy systems

Software engineering

Tools

Claude Code

Cursor

GitHub Copilot

Codex

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