Senior Full-Stack Software Engineer
Onhires
Location: Barcelona, Spain (Hybrid)
Employment: Full-time
About Our Client
Our client is building the AI platform that will redefine the future of hardware engineering.
Their product brings together system architecture, requirements, verification, and engineering workflows into one intelligent platform, helping engineering teams design and build the world's most advanced hardware systems faster and more efficiently.
From aerospace and defense to robotics, transportation, and semiconductor technologies, they're creating the AI infrastructure that will power the next generation of engineering.
This is an early-stage company where every engineer has a direct impact on the product, the technology, and the future of the business.
About the Role
As a Senior Full-Stack Software Engineer, you'll work directly with the founders and technical leadership to build a next-generation AI product from the ground up.
This is a highly hands-on engineering role where you'll own features end-to-end-from architecture and implementation to deployment and continuous improvement. You'll collaborate closely with customers, help solve complex engineering challenges, and influence both product and technical decisions.
If you're excited by ownership, modern AI technologies, and building products that solve meaningful real-world problems, this is an opportunity to make a significant impact from day one.
What You'll Do
Own product development from concept to production
Design and build scalable full-stack applications
Develop modern backend services and intuitive frontend experiences
Translate customer needs into elegant technical solutions
Write clean, maintainable, production-ready code
Collaborate directly with founders, engineers, and customers
Review code and contribute to engineering best practices
Improve infrastructure, CI/CD pipelines, cloud deployments, and observability
Build and integrate AI-powered capabilities across the platform
Help shape the engineering culture as the team grows
What We're Looking For
Required
3-6+ years of professional software engineering experience
Strong experience building production SaaS applications
Excellent TypeScript skills across the full stack
Experience with React (or another modern frontend framework)
Strong backend development experience and API design
Solid understanding of PostgreSQL or other relational databases
Experience with Docker, CI/CD, and cloud infrastructure (AWS, GCP, or Azure)
Strong debugging, analytical, and problem-solving skills
Product mindset with the ability to take ownership from idea to delivery
Comfortable working in a fast-moving startup environment
Experience using AI development tools and modern LLM workflows
Fluent English
Based in Barcelona or willing to relocate
Nice to Have
Startup or founding engineering experience
Experience building AI-powered applications
Knowledge of RAG, vector databases, or multi-agent systems
Enterprise SaaS experience
Interest in aerospace, robotics, semiconductor, automotive, or other advanced engineering industries
Tech Stack
You'll work with modern technologies including:
TypeScript
React
PostgreSQL
REST / tRPC APIs
Docker
GitHub Actions / CI/CD
AWS, GCP, or Azure
AI development tools and LLM workflows
Why Join?
Build a category-defining AI platform from an early stage
Work directly with experienced founders and technical leaders
Own meaningful product decisions and features from day one
Solve challenging engineering problems with real-world impact
Competitive salary plus meaningful equity
Join a high-performing team where your work will directly shape the future of the company
Additional Information
Hybrid role based in Barcelona, Spain
Applicants must have the right to work in the EU
Some projects may require eligibility for NATO security clearance due to collaboration with aerospace and defense organizations
Language learning is supported by the company