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Senior AI Engineer - Node.js / Next.js / TypeScript

Ruby LabsEuropean Union
On-site Full-time

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Experience Level

Senior

Qualifications

Key ResponsibilitiesAdvanced Prompt Engineering: Crafting intricate, dynamic prompt templates that utilize conditional logic to enhance generation quality and reasoning through the efficient reuse of information and context. Structured Outputs & Schemas: Implementing diverse response schemes (JSON mode, function calling, Zod/JSON schemas) to ensure AI outputs are predictable and seamlessly integrated into application logic. Prompt Engineering & Evaluations: Establishing robust evaluation pipelines and utilizing Langfuse to gather feedback and assess response quality in real-time. Tracing & Debugging: Conducting in-depth debugging of complex LLM chains using Langfuse traces to pinpoint bottlenecks and optimize for cost, latency, and context window utilization. AI A/B Testing: Executing systematic experiments across various models via OpenRouter (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 based on quantitative benchmarks and trace data, rather than instinct. Output Scoring & Analysis: Creating scoring systems to analyze the "Problem → Solution" chain and identify the root causes of hallucinations or logic errors using Langfuse analytics.

About the job

Ruby Labs builds and manages consumer products across health, education, and entertainment. The team focuses on practical, user-driven solutions and values technical curiosity. Learn more about the company at https://rubylabs.com/about-us/.

Role Overview

This Senior AI Engineer position centers on Node.js, Next.js, and TypeScript. The role shapes AI infrastructure and improves production-ready large language model (LLM) experiences. Day-to-day, the engineer makes data-driven decisions that affect model performance, reliability, and cost control.

What You Will Do

  • Develop prompt systems for LLMs and manage structured outputs.
  • Design and orchestrate complex LLM workflows using tools such as LangChain and LlamaIndex.
  • Maintain observability and strong debugging practices, using Langfuse and AI gateways like OpenRouter.
  • Drive model quality and operational efficiency from experimentation through live production.
  • Take full ownership of key AI features, ensuring they are robust and production-ready.

Location

This role is open to candidates based in the European Union.

About Ruby Labs

Ruby Labs is at the forefront of technology, dedicated to crafting and managing innovative consumer products across various sectors. Our commitment to innovation drives us to develop solutions that truly resonate with consumers. Join us to be part of a team that is shaping the future of consumer-centric technology.

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