Staff AI Engineer API & Integrations Team (Barcelona)

Hello!

Do you want to help us redefine how AI powers the future of Business Management software not as an add-on but as a core part of how people work decide and grow

Were looking for engineers who:

• Treat AI as central to their craft not a feature to bolt on later
• Want to build and ship not debate and document
• Care about whether the thing they built actually worked not what their title says.

Ready to be part of the challenge

About the team

Our Engineering team is the engine behind Factorial crafting the tech that makes HR simple fast and reliable for thousands of companies. If you love solving hard problems and want to build something that truly matters come build it with us.

Were a team of 200 Product Engineers building Business Management solution that actually works for the people using it. Our core stack is Ruby on Rails and React but the interesting work right now is what were building on top of that: agentic workflows LLM-integrated features systems that behave probabilistically rather than deterministically.

The API & Integrations team addresses particular challenges at Factorial. We sit at the intersection between product and platform. We own product surface while we also design developer experiences for internal and external developers of integrations.

• We build tools for Factorial product teams to publish in our extensive public API.
• We build an integrations framework to achieve the best user experience and developer experience when using integrations. Several factorial products are already using this framework. And we keep expanding it.
• We enable our developer partners to extend Factorial and live the best developer experience. With the acquisition of YepCode we will be boosting how we build integrations placing AI at the center of the process.

Our mission is not only to unblock markets that rely on a fragmented market of different external software (payroll software solutions ERPs cloud-based identity services etc.) but also to lower the barrier so that anybody (even HR managers) is able to create new integrations.

What Youll Do

As a Product AI Engineer at Factorial youll help define and build the next generation of our AI-native product using modern AI development practices.

You will:

• Build product using Spec Driven Development
  We define clear specifications before shipping including expected behaviours constraints and success criteria and use them to guide implementation iteration and evaluation using most powerful LLMs.
• Design and implement AI Skills
  Create reusable well-scoped AI capabilities that can automate and take actions safely within Factorials workflows and also when building integrations
• Develop and maintain evaluation frameworks (Evals)
  Measure quality correctness and reliability of AI outputs using automated and human-in-the-loop evaluations to ensure continuous improvement in production.
• Apply Retrieval-Augmented Generation (RAG)
  Build systems that ground AI responses in trusted up-to-date company data balancing probabilistic models with deterministic sources of truth.
• Design human-in-the-loop and agentic workflows
  Combine LLMs rules and user oversight to automate real business processes while keeping humans in control of critical decisions.
• Own systems end-to-end
  From problem definition and system design to shipping monitoring and iteration in production.
• Stay close to our customers
  We have a strong customer-centric mindset: engineers regularly join customer calls reviews and feedback sessions to deeply understand real workflows pain points and constraints ensuring we build the right solutions to real problems not assumptions.
• Collaborate closely with Product and Design
  Shape how AI is embedded into core user experiences not as a feature but as part of the workflow.
• Share knowledge and raise the bar
  Mentor peers document learnings and contribute to Factorials AI engineering best practices.

What are we looking for

Your title matters less than your mindset.

You might be mid senior or staff. What we care about is:

• AI as a habit: youve built real AI-powered systems or workflows (not just experiments)
• Proven impact: shipped projects side projects or contributions that made a measurable difference
• Product-first thinking: you design complete experiences not just isolated components
• Speed & adaptability: you experiment learn and iterate fast

Bonus points if youve worked with:

LLMs skill-based agents MCP or other AI protocols

Technical Foundation (Not Strict Requirements)

Strong candidates often have:

• Solid software engineering fundamentals (any language backend frontend ML)
• Experience shipping real products to production
• Knowledge of APIs cloud platforms and system design
• A fast learning curve with new tools and technologies

We care far more about what youve built than the stack you used.

How We Work (Barcelona or Madrid Office)

At Factorial we believe the best products are built when people come together in person to collaborate challenge ideas and move fast. Thats why our Engineering Teams follows an office-first flexible schedule.

We work on-site several days a week using that time to connect align and innovate as a team. However we also understand the importance of focus and flexibility so we support remote work when it makes sense - whether for deep work personal needs or just a change of scenery.

This balance helps us stay agile creative and closely connected while giving everyone the space to do their best work.

At Factorial we dont evaluate you by years of experience but by your knowledge and skills.

We use our Career Path with a rubric framework where we define what is expected for each experience level and skill. This framework allows you to know your current level and what you need to keep growing. We love transparency so our Career Path includes the salaries for each level which we share during the first interview to ensure alignment.

Our Hiring Process

1. Intro Call Chat with our Talent Partner about your journey and goals.
2. Hiring Manager Interview Deep dive into your product mindset teamwork and problem-solving.
3. Live Challenge A collaborative technical exercise based on real-life problems.
4. Final Coffee Chat A relaxed conversation with our CTO & VP of Engineering to explore our vision culture and your growth.

The whole process is remote using videoconferencing tools!

About Factorial

At Factorial were building the leading AI Business Management Software for companies of all sizes. Our platform centralizes key workflows across HR Finance Talent Operations and IT freeing teams from manual processes so they can focus on what really matters: leading growing and taking care of their over 1500 employees across Europe Asia Africa and America. We are one of Europes fastest-growing SaaS companies proudly headquartered in Barcelona. If youre excited to shape the future of business management technology wed love to meet you.

We believe in diverse talent: we welcome applicants from all backgrounds and strongly encourage people of diverse experiences and identities to apply.

We believe in inclusion: we are committed to equal opportunities and actively promote workplace inclusion of people with disabilities. If you would like to learn more about our inclusive recruitment processes you are welcome to indicate so optionally and we will share additional information with you.

Our Values

• We own it: We take responsibility for every project. We make decisions not excuses.
• We learn and teach: Were dedicated to learning something new every day and above all share it.
• We partner: Every decision is a team decision. We trust each other.
• We grow fast: We act fast. We think that the worst mistake is not learning from them.

Wanna learn more about us Check our website!

Perks of being part of Factorial

High growth multicultural and fri...