Principal Engineer

RedRock Resourcing; Reading; On-site; GBP 70,000 - 120,000; Full time

Job summary

RedRock Resourcing seeks three experienced Software Engineers to join a brand-new agentic engineering team. You will modernise legacy software using AI and agentic techniques, going beyond traditional ticket-based work.

You'll operate at the intersection of software engineering, architecture, AI, and developer experience to design systems, standards and guardrails that enable engineers to deliver better software safely.

Qualifications

• Serious for a strong software engineering foundation and experience with complex legacy systems.
• Deep experience in C#/.NET or Java; depth in one stack preferred over breadth across many stacks.
• Willingness to work on AI-assisted software engineering and agentic development; knowledge of automated testing is a plus.

Responsibilities

• 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.
• Build repository-level instructions, agent skills, prompts and dynamic context.
• Work with agentic development tools like Claude Code, MCP and related tooling.
• Establish automated testing and AI evaluation frameworks to balance speed and quality.
• Build guardrails, sandboxes and CI/CD controls around AI-driven development.

Skills

Strong software engineering foundation

C#/.NET or Java

Experience with large/legacy systems

Depth in one stack

Tools

Claude Code

Cursor

GitHub Copilot

Codex

Job description

Senior / Principal Software Engineer – Agentic Engineering

We're looking for three experienced Software Engineers to join a brand-new team.

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?

• 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 or Java, alongside experience working with large, complex or legacy systems.

You might have worked with:

You don't need both stacks. Depth in one is far more important than claiming experience across everything.

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