AI-Driven Principal Engineer: Agentic Legacy Modernisation

RedRock Resourcing; Reading; On-site; GBP 110,000 - 160,000; Full time

Job summary

Agentic Engineering is seeking a Principal Software Engineer to lead AI-driven modernisation of complex legacy systems. You will shape the engineering harness and governance around AI agents, work across architecture and developer experience, and drive high-quality, scalable software delivery.

You’ll collaborate with teams to implement automated testing, evals and robust guardrails, ensuring safe, rapid evolution of critical codebases using Claude Code, MCP and other agentic tools.

Qualifications

• Strong software engineering foundation, especially in C#/.NET.
• Experience with large, complex or legacy systems.
• Knowledge of AI-assisted software development and agentic tooling.

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.
• Establish automated testing and AI evaluation frameworks to ensure quality.
• Build guardrails, sandboxes and CI/CD controls around AI-driven development.

Skills

C#/.NET

AI & agentic engineering

Tools

Claude Code

MCP

GitHub Copilot

Codex

Cursor

Job description

Agentic Engineering is seeking a Principal Software Engineer to lead AI-driven modernisation of complex legacy systems. You will shape the engineering harness and governance around AI agents, work across architecture and developer experience, and drive high-quality, scalable software delivery.

You’ll collaborate with teams to implement automated testing, evals and robust guardrails, ensuring safe, rapid evolution of critical codebases using Claude Code, MCP and other agentic tools.