Principal Software Engineer

RedRock Resourcing; Reading; On-site; GBP 90,000 - 130,000; Full time

Job summary

RedRock Resourcing is seeking a Principal Software Engineer – Agentic Engineering to advance legacy modernisation through AI‑driven software engineering. You will shape the intersection of software engineering, AI, and developer experience, building systems, standards and guardrails for safer, faster delivery.

You will work hands‑on with complex legacy tech, designing an AI‑driven engineering harness and implementing tooling to modernise codebases while maintaining quality and safety.

Qualifications

• Requires a seriously strong software engineering foundation.
• Experience with large, complex or legacy systems is essential.
• Comfort with refactoring, architecture decisions and modernisation strategies.

Responsibilities

• Hands‑on work with complex legacy technology while applying AI tooling.
• Design the engineering harness to give AI agents proper context, rules and constraints.
• Build repository‑level instructions, agent skills, prompts and dynamic context.
• Collaborate on automated testing, evals and quality frameworks for AI‑driven development.
• Establish guardrails, sandboxes and CI/CD controls for AI‑enabled software engineering.

Skills

Strong software engineering

C#/.NET

AI tooling familiarity

Tools

Claude Code

GitHub Copilot

Codex

Cursor

MCP

Job description

Principal Software Engineer – Agentic Engineering

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:

• 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

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