AI Engineer (Node.js)

TL;DR

AI Engineer (Node.js/TypeScript): Shaping AI infrastructure and driving production-ready LLM experiences with an accent on prompt systems, structured outputs, and complex LLM workflows. Focus on building robust evaluation pipelines, performing deep debugging of LLM chains, and optimizing model performance based on quantitative metrics.

Location: Remote, must be located within approximately ± 4 hours of CET

Company

Ruby Labs is a leading tech company that creates and operates innovative consumer products in the health, education, and entertainment industries.

What you will do

• Design complex, dynamic prompt templates with conditional logic to maximize generation quality and reasoning.
• Implement structured response schemes (JSON mode, function calling, Zod/JSON schemas) for seamless application integration.
• Build evaluation pipelines and leverage Langfuse to collect real-time feedback and score response quality.
• Debug complex LLM chains to identify bottlenecks and optimize for cost, latency, and context window usage.
• Run systematic A/B tests across different models via OpenRouter and analyze results using quantitative metrics.
• Perform model fine-tuning when necessary to meet specific domain requirements.

Requirements

• Deep knowledge of Node.js and Next.js for building reliable services and handling LLM-generated data.
• Proven experience in dynamic prompting and context injection.
• Experience with OpenRouter for managing unified APIs and cost-effective model selection.
• Understanding of LLM observability (tracing, test datasets, scoring systems) using Langfuse or similar tools.
• Experience with evaluation frameworks like RAGAS or custom LLM-as-a-judge systems.
• Location: Must be based in a region within ± 4 hours of CET.

Nice to have

• Practical experience in fine-tuning models for domain tasks or JSON compliance.
• Knowledge of RAG architecture, including indexing, retrieval, and re-ranking.
• Basic Python knowledge for data science scripts or AI evaluation libraries.

Culture & Benefits

• Remote work environment promoting a healthy work-life balance.
• Unlimited paid time off (PTO).
• Paid national holidays.
• Company-provided MacBook for all employees.
• Flexible independent contractor agreement with associated tax advantages.

Hiring process

• Recruiter Screening (40 minutes).
• Technical Interview (60 minutes).
• Final Interview (30 minutes).