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Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md). --- # AI Engineer - **Company:** Ruby Labs - **Location:** Eu, France (Remote available) - **Experience:** Expert - **Contract:** Permanent contract - **Skills:** A/B Testing, Application Programming Interfaces (APIs), Artificial Intelligence, Business Logic, Software Debugging, JSON, Python (Programming Language), Node.Js, Performance Tuning, Next.js, TypeScript, AI Infrastructure, Retrieval-Augmented Generation, Large Language Models, Prompt Engineering, Model Validation, Indexer, Data Analytics - **Published:** May 15, 2026 - **Apply:** https://fr.indeed.com/viewjob?jk=588e8565841b2d39 ## About the Role Do you have experience in TypeScript?, * 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. * OpenRouter 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. * Fluency in Russian and/or Ukrainian., * 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. ## Description We are looking for a Senior AI Engineer (Node.js / Next.js / TypeScript) to join our team and help advance our AI infrastructure. You'll work within a modern tech stack, focusing on model performance, reliability, and cost efficiency. You'll take ownership of prompt systems, structured outputs, and LLM workflows built on LangChain or LlamaIndex. The role also covers observability and evaluation using Langfuse and AI gateways such as OpenRouter, with the goal of consistently improving model quality and operational efficiency. You'll drive key AI features from early experimentation all the way through to 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 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 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. ## Related Videos - [Tips and Tricks for Working with JSON](https://www.wearedevelopers.com/videos/1229-tips-and-tricks-for-working-with-json) - [Optimizing Discovery: PostgreSQL's Role in Transforming GetYourGuide's Search](https://www.wearedevelopers.com/videos/1647-optimizing-discovery-postgresql-s-role-in-transforming-getyourguide-s-search) - [GraphQL + Apollo + Next.js: A Lovely Trio](https://www.wearedevelopers.com/videos/311-graphql-apollo-next-js-a-lovely-trio) - [Bringing the power of AI to your application.](https://www.wearedevelopers.com/videos/1010-bringing-the-power-of-ai-to-your-application) - [Dynamic Entities in .NET: Building Low-Code Systems on Top of Entity Framework Core](https://www.wearedevelopers.com/videos/100218-dynamic-entities-in-net-building-low-code-systems-on-top-of-entity-framework-core) - [Introducing JSON Structure](https://www.wearedevelopers.com/videos/100219-introducing-json-structure) ## Related Articles - [What Are Large Language Models?](https://www.wearedevelopers.com/magazine/304-what-are-large-language-models) - [Dev Digest 121 - AI goes offline](https://www.wearedevelopers.com/magazine/456-dev-digest-121-ai-goes-offline) - [Dev Digest 120 - Apple and peers](https://www.wearedevelopers.com/magazine/455-dev-digest-120-apple-and-peers) - [Dev Digest 137 - AI'm not sure about this](https://www.wearedevelopers.com/magazine/485-dev-digest-137-ai-m-not-sure-about-this) - [Dev Digest 131 - AI'm not sure about OSS](https://www.wearedevelopers.com/magazine/472-dev-digest-131-ai-m-not-sure-about-oss) - [Navigating the AI Shift](https://www.wearedevelopers.com/magazine/629-navigating-the-ai-shift)