Software Engineer

About Systellar
Every complex machine, a satellite, a commercial aircraft, a high-speed train, is built by hundreds of engineers across dozens of disciplines trying to stay aligned on something that has never been built before. Today they do it with spreadsheets, email threads, and tools designed for a different era.

synapse™ is the platform that changes this: an engineering environment where hardware systems are designed, validated, and evolved with full traceability across every team, every discipline, and every decision. We are Barcelona-based, ESA BIC-supported, and Techstars-backed.

The role
This is a founding engineering hire. We are not looking for someone to fit into an existing engineering culture, we are looking for someone to help define it. You will work directly with the founding team, own significant parts of the product, and have a real seat at the table on architecture, priorities, and what we build next. As we grow, you will help build the team around you.

You will work full-stack across the whole product: data model, backend, frontend, QA, and infrastructure. You will define how the engineering team works, from code structure and review processes to agentic development and the hiring bar. You will own infrastructure end to end, contribute to R&D programmes with research and industry partners, and engage with customers directly to turn their workflows into product decisions.

What we look for

• 3 to 6 years of professional software engineering experience
• Based in Barcelona or willing to relocate
• Strong technical foundations: you reason from first principles and understand what happens beneath the abstractions
• Full-stack range, with real product sensibility for users and workflows
• You move fast and obsess over quality, both non-negotiable
• You use AI tools fluently, but your instincts were built before they existed
• Clear, direct communicator in writing, in conversation, and in front of customers
• English required. Willigness to learn Catalan and Spanish (language learning sponsored)

Stack and technology
TypeScript, tRPC, React, relational and vector databases, Docker, CI/CD, cloud infrastructure, observability, and agentic systems (MCP servers, state graphs, production agent debugging). We are not looking for a checklist match, but for someone who has thought carefully about the layers of a modern software system.

Nice to have
Early-stage or founding team experience, curiosity about aerospace, defence, automotive, or railway, and enterprise software background.

To read the full job description and apply: link