AI Engineer

About us

Ruby Labs is a leading tech company that creates and operates innovative consumer products. We offer a diverse range of opportunities across the health, education, and entertainment industries. Our innovative teams are driving the future of consumer-led products, and we're always looking for passionate individuals to join us. Learn more about our story at:

At Ruby Labs, we’re seeking a senior AI Engineer (Node.js / Next.js / Type Script) to shape our AI infrastructure and drive production-ready LLM experiences. You’ll work in a modern stack, making data-driven decisions around model performance, reliability, and cost.

You’ll own advanced prompt systems, structured outputs, and complex LLM workflows using Lang Chain or Llama Index. Observability, debugging, and evaluation are core to the role, leveraging Langfuse and AI gateways like Open Router to continuously improve model quality and operational efficiency. You’ll take full ownership of key AI features from experimentation to live production.

• Advanced Prompt Engineering:
  Designing complex, dynamic prompt templates with conditional logic and efficiently reusing information and context within prompts to maximize generation quality and reasoning.
• Structured Outputs & Schemas:
  Implementing various response schemes (JSON mode, function calling, Zod/JSON schemas) to ensure AI outputs are predictable and ready for seamless integration into application logic.
• Prompt Engineering & Evaluations:
  Building robust evaluation pipelines and using Langfuse to collect feedback and score the quality of responses in real time.
• Tracing & Debugging:
  Performing deep debugging of complex LLM chains using Langfuse traces to identify bottlenecks and optimize for cost, latency, and context window usage.
• AI A/B Testing:
  Running systematic experiments across different models via Open Router (e.g., comparing Claude 3.5 Sonnet vs. GPT-4o) and analyzing results based on quantitative metrics.
• Data-Driven Decisions:
  Making deployment decisions for new prompts or models strictly based on quantitative benchmarks and trace data, rather than intuition.
• Output Scoring & Analysis:
  Developing scoring systems to analyze the “Problem → Solution” chain and identify root causes of hallucinations or logic errors using Langfuse analytics.
• Model Performance & Fine-Tuning:
  Regularly re-evaluating model performance as new architectures emerge and performing fine-tuning when necessary to meet specific domain requirements.

• Node.js & Next.js:
  Deep knowledge of the stack to build reliable services and handle complex LLM-generated data.
• Dynamic Prompting
  
  Skills:
  
  Proven experience in building prompts where content is highly dependent on input variables and context injection.
• Open Router
  
  Experience:
  
  Experience working with unified APIs, managing rate limits, and selecting the most cost-effective models for specific tasks.
• Langfuse (or similar):
  Understanding of LLM observability principles — setting up tracing, creating test datasets, and integrating scoring systems.
• Evaluation Methodology:
  Experience with frameworks like RAGAS or building custom “LLM-as-a-judge” systems.
• Analytical Mindset:
  Ability to transform raw generation logs into actionable business metrics and technical insights.
• Iterative Mindset:
  Focus on continuous product improvement through constant feedback loops.

• Fine-Tuning:
  Practical experience in fine-tuning models for specific domain tasks or JSON compliance.
• RAG Architecture:
  Understanding how to build and optimize Retrieval-Augmented Generation systems, including indexing, retrieval, and re-ranking.
• Python:
  Basic knowledge for working with data science scripts or AI evaluation libraries.

Ruby Labs operates within the CET (Central European Time) zone. Applicants from any country are welcome to apply for the position as long as they are located within approximately ± 4 hours of CET. This ensures optimal collaboration and communication during working hours.

Discover the perks of being part of our vibrant team! We offer:

• Remote Work Environment
  :
  Embrace the freedom to work from anywhere, anytime, promoting a healthy…