Senior Backend Engineer - Ruby on Rails

Confidential; Barcelona; Remote; EUR 70,000 - 90,000; Full time

Job summary

Ersilia in Barcelona is hiring a senior backend engineer to own a critical production system, contribute to the roadmap, and bring new ideas through experiments. You will work hands-on on a Ruby on Rails stack, ensuring reliability and performance while collaborating with engineering and product teams.

The role demands 5+ years of production experience, an AI-first mindset with Cursor/Claude Code/Codex, and an autonomous work style with advanced English.

Qualifications

• 5+ years building and maintaining production systems as backend engineer.
• Strong experience with Ruby on Rails in large-scale products.
• AI-first mindset using tools like Cursor, Claude Code and Codex.
• Experience owning business-critical systems and debugging complex issues.
• Ability to work autonomously with high ownership and advanced English.

Responsibilities

• Hands-on code implementation, code reviews, testing.
• Ensure reliability, performance and correctness of systems.
• Diagnose and resolve complex production issues.
• Collaborate with other engineering and product teams.
• Make pragmatic decisions balancing risk, maintainability and business needs.
• Improve code quality and internal structure where possible.

Skills

Ruby on Rails

Backend engineering

Debugging

Autonomous work

English (Advanced)

Tools

Cursor

Claude Code

Codex

Job description

You will take ownership of a backend system that is critical to the company and our customers. You will have the opportunity to help define our roadmap and find the best technical solutions. You will also have time to run some experiments and bring new ideas to the table.

Your responsibilities:

• Hands-on code implementation, code reviews, testing
• Ensure reliability, performance and correctness.
• Diagnose and resolve complex production issues.
• Collaboration with other engineering & Product teams.
• Make pragmatic decisions balancing risk, maintainability, and business needs.
• Improve code quality and internal structure where possible.

What we are looking for:

• 5 years plus experience building and maintaining production systems as backend engineer
• Strong experience with Ruby on Rails
• AI-first mindset using tools like Cursor, Claude Code, Codex, in your daily workflow
• Working on large-scale products
• Experience owning systems that are business critical.
• Methodical approach to debugging and problem solving.
• Comfortable working autonomously with high ownership.
• Advanced level of English.

Tech Stack:

• Language & Platform: Ruby
• Data: PostgreSQL or Redis
• Infrastructure: Tailwind

Location:

Barcelona, Spain > or Fully remote within a +/- 4hrs CET