[Hiring] Junior AI Engineer @Ruby Labs

Role Description

At Ruby Labs, we are building a Direct-to-Consumer product in the AI category. We’re looking for a Junior AI Engineer (Node.js / Next.js / TypeScript) to join our AI engineering team and contribute to production-ready LLM experiences.

You’ll work alongside senior engineers in a modern stack, learning to make data-driven decisions around model performance, reliability, and cost. You’ll contribute to prompt systems, structured outputs, and LLM workflows while building familiarity with observability and evaluation tooling like Langfuse and AI gateways like OpenRouter.

This is a hands-on role where you will grow quickly by shipping real AI features to production under the guidance of experienced teammates.

Key Responsibilities

• Implement AI-powered product features and workflows based on specifications from senior engineers.
• Write, iterate on, and manage production prompt templates, following established patterns for dynamic prompting and context injection.
• Integrate structured output schemas (JSON mode, function calling, Zod/JSON schemas) to ensure AI responses are predictable and application-ready.
• Build and maintain output enforcement mechanisms such as validators and repair loops under senior guidance.
• Participate in prompt experimentation workflows — drafting variants, running A/B tests across models via OpenRouter, and documenting results.
• Contribute to evaluation pipelines and help score prompt/model quality using Langfuse.
• Write clean, maintainable TypeScript code within the Next.js / Node.js stack.
• Participate in code reviews and incorporate feedback.
• Document technical decisions and system behaviour to support knowledge sharing.
• Collaborate with product, growth, data, and billing teams to deliver features on time.

Qualifications

• Working knowledge of Node.js, Next.js, and TypeScript.
• Basic understanding of how LLMs work and hands-on experience using LLM APIs (OpenAI, Anthropic, or similar).
• Experience writing prompts that go beyond simple instructions — e.g., using variables, templates, or conditional logic.
• Familiarity with structured outputs (JSON mode, function calling, or schema validation).
• Understanding of basic web application architecture and RESTful APIs.
• Curiosity and willingness to learn quickly in a fast-moving AI product environment.
• Strong communication skills and a collaborative mindset.

Nice to have

• Experience with AI-centred development tools (Cursor, Claude Code, Windsurf, or similar).
• Experience with LLM observability tools (Langfuse, LangSmith, or similar).
• Exposure to AI gateways like OpenRouter or model routing concepts.
• Familiarity with evaluation frameworks (RAGAS, custom LLM-as-a-judge systems).
• Experience with Redis or real-time data systems.
• Experience working in startup or fast-paced product environments.

Location

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.

Benefits

• Remote Work Environment: Embrace the freedom to work from anywhere, anytime, promoting a healthy work-life balance.
• Unlimited PTO: Enjoy unlimited paid time off to recharge and prioritize your well-being, without counting days.
• Paid National Holidays: Celebrate and relax on national holidays with paid time off to unwind and recharge.
• Company-provided MacBook: Experience seamless productivity with top-notch Apple MacBooks provided to all employees who need them.
• Flexible Independent Contractor Agreement: Unlock the benefits of flexibility, autonomy, and entrepreneurial opportunities. Benefit from tax advantages, networking opportunities, reduced employment obligations, and the freedom to work from anywhere.