Senior Ruby on Rails Developer (LLM) at OnTheGoSystems · Serbia

We are looking for a senior Ruby on Rails developer to help us build reliable, scalable products and apply AI/LLM technologies where they create real value.

This is a hands-on engineering role for someone who can own complex features end to end, make strong technical decisions, and work across backend architecture, production systems, testing, and AI-assisted product development.

You should be excited about AI, but pragmatic enough to know when a simple, deterministic solution is better than an LLM call.

What you’ll be working on:

• Owning features from technical design to production
• Building and maintaining Ruby on Rails systems used at scale
• Designing AI/LLM-assisted features and workflows where they improve product quality or user experience
• Working with LLM APIs, prompts, retrieval/context strategies, and AI-assisted development tools
• Making trade-offs around performance, reliability, cost, latency, security, and maintainability
• Writing and maintaining automated tests, including unit, integration, and E2E tests
• Debugging production issues and improving system reliability

What we’re looking for:

To succeed in this role, you’ll have:

• Strong professional experience with Ruby on Rails, ideally at senior level
• Experience building and running production systems used by real customers
• Strong backend skills, including databases, API design, performance, background jobs, and security;
• Ability to break down ambiguous problems and propose practical technical solutions
• Hands-on interest or experience with AI/LLM technologies,
• Good judgment about when to use AI and when simpler engineering approaches are better
• Strong testing habits and care for long-term code quality
• A responsible, curious, flexible mindset: willing to debug, deploy, investigate, learn, and own outcomes

Nice to have:

• Experience with React
• CI/CD, background jobs, or AWS experience
• Experience building AI-powered product features in production
• Familiarity with embeddings, vector search, RAG, evals, or LLM observability
• Experience with text-processing, localization, translation, or multilingual products

Why Join OTGS?

• Stable & self-funded: Founded in 2007, profitable, and independent.

• Industry leaders: Creators of WPML, the #1 multilingual plugin for WordPress, used on 1.5M+ sites

• Fully remote, async-friendly: Work from anywhere within EMEA hours

• Engineering-driven culture: Ownership, autonomy, testing, and thoughtful problem-solving

• Fair compensation and great benefits: Designed to support your well-being both inside and outside of work.