Senior Software Engineer (AI Native)

In this AI-native Senior Software Engineer role, you design and oversee Castle’s fintech platform, guiding AI agents to deliver production software. You own architecture, reviews, and outcomes, while automation and agent tooling accelerate delivery. You work within an agile, start-up–like squad to disrupt financial services with AI-enabled software. The role combines hands-on supervision of AI-generated code with strong engineering governance. You’ll collaborate cross-functionally to ship high-quality solutions at pace.

• Hybrid working
• 24 days holiday + 8 bank holidays (+ option to buy 10 more)
• Annual bonus scheme
• Company pension with up to 8% contribution
• Mental health support
• Paid volunteer time

• Direct AI agents to code, test, document, and refactor complex programs and services, taking ownership of outputs
• Contribute to choice of software development methods, AI agents, tools and techniques
• Encode standards into agent instructions, context, and guardrails for quality outcomes
• Rigorously review agent-generated code and guide peers’ work reviews
• Design complex applications and break work into agent-executable tasks
• Review and refine own designs and lead peer design reviews
• Utilize approved deployment tools and agent workflows for delivery
• Identify and resolve application issues with agents to accelerate fixes
• Use management tools to collect performance statistics
• Continuously improve agentic development workflows and share learnings

• AI-native software development with coding agents (Claude Code, GitHub Copilot, Cursor)
• Context engineering: writing specifications, agent instructions, and guardrails
• JavaScript/Typescript proficiency with capability to review agent code
• Hands-on Node serverless microservices (AWS Lambda, ECS)
• Familiarity with AWS serverless and deployment frameworks (Serverless, AWS SAM, AWS CDK)
• API-first software development approach
• Unit and integration testing with Jest
• Experience consuming RESTful services and handling JSON
• CI practices and source control (Git) with Azure DevOps or GitLab or similar
• Agile development methodologies
• Terraform knowledge or willingness to learn IaC
• Kafka familiarity or willingness to learn
• Understanding of software design patterns
• Awareness of risks in AI-generated code and mitigation strategies

• Collaborative mindset
• Bias for action and adaptability
• Strong analytical and problem-solving abilities
• AI-native development
• Coding agents (Claude Code, Copilot, Cursor)
• Context engineering