? We’re building Mainloop AI in Barcelona: a new AI-native engineering team focused on building production-grade software with coding agents from day one.

Mainloop AI is being created to build and scale software products that automate professional-services work across roughly 15 countries. The team will work on internal platforms, agent-native products and tools that move beyond prototypes into software businesses actually depend on.

This is not a traditional engineering team adding AI on top. Mainloop AI is being built AI-native from the first commit: engineers will work with coding agents such as Claude Code, Cursor, Codex or similar as part of the core development process, with a strong focus on architecture, judgement, testing and production quality.

We’re now hiring the first Full-Stack Engineers to join Mainloop AI in Barcelona:

? 4 junior positions

? 1 senior position

What you’ll do

You’ll work on real products alongside a Product Owner. Each product is owned by a two-person team: the PO leads the relationship with the business, the needs and the roadmap; you lead the architecture, quality, build and release.

Your responsibilities will include:

- Taking ownership of products used by teams across different countries.
- Turning prototypes into robust, maintainable, production-ready software.
- Designing architecture and making technical decisions with long-term impact.
- Working with AI coding agents as a central part of the development process.
- Reviewing, validating and improving code generated by agents.
- Ensuring quality through unit, smoke and end-to-end testing.
- Evolving existing products and contributing to new ones.




- Helping define the technical standards and ways of working of a new team.

Here, AI does not replace engineers — it gives them more leverage. The value is in your technical judgement, your ability to define what should be built, and your ownership of products in production.

What we’re looking for

We don’t expect you to tick every box from day one, especially for the junior roles. We’re looking for people with potential, judgement and a strong appetite to learn.

We’d like to hear from you if:

- You have built web applications end to end, whether at work, university, bootcamp or through personal projects.
- You’re comfortable across both frontend and backend.
- You have experience with, or a strong interest in, TypeScript.
- You’ve used coding agents such as Claude Code, Cursor, Codex or similar.
- You can read AI-generated code critically.
- You understand the importance of testing and production quality.
- You can pick up a codebase you didn’t write and understand it before changing it.
- You speak fluent English. Spanish is useful day to day.
- You are based in Barcelona or want to work onsite with the team there.

For junior profiles, the essentials are simple: you can build a working web application, you’ve used AI coding agents seriously enough to have opinions, and you want to get good fast.

For the senior profile, we’re looking for someone who has owned production software and can define the architecture others will build within.

? Location: Barcelona

? Employment type: Full-time

- If you want to join a new team at the very beginning, backed by an international group, and build software in a genuinely AI-native way, apply through the link in the job post.

📌 Full Stack Engineer (San Cugat del Vallés)
🏢 Leyton
📍 San Cugat del Vallés