Staff Software Engineer

Factorial

Madrid

Hybrid

EUR 90,000 - 130,000

Full time

5 days ago

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Benefits offered by this job

High growth environment

Competitive ESOP plan

Private health insurance

Wellbeing and fitness programs

Office snacks & fruit

Job summary

Factorial is seeking a Staff Software Engineer to build AI-native features using Rails and React. You’ll lead technical initiatives, work closely with Product and Design, and ship real features in production.

You’ll design scalable systems, run AI-enabled product experiences, and ensure reliability and compliance across teams. You’ll influence architecture, own end-to-end delivery, and push for reusable components while mentoring others.

Qualifications

Experience shipping production software with strong backend and frontend skills.
Proven ability to ship features using Rails and React in production.
Experience integrating LLM APIs into product features and shipping to users.
Excellent API, cloud platform, and system design knowledge.
Ability to lead technically and align with Product and Design teams.
Clear English communication; Spanish is a plus.

Responsibilities

Lead technical initiatives and set direction for roadmap chunks.
Collaborate closely with Product and Design from early conversations.
Own end-to-end systems from problem discussion to production maintenance.
Engage with customers to inform technical decisions.
Define AI feature design, scale, reliability, and governance.
Promote spec-driven development and reusable components.

Skills

Backend & Frontend

Rails

React

LLM APIs

API design

Cloud platforms

Leadership

English communication

Tools

Rails

React

Job description

Hello! We’re looking for a Staff Software Engineer to help build AI-native features into Factorial’s product. Not a researcher, not a model trainer: a product engineer who builds with LLM APIs the same way we build with any other API, shipping real features to real customers in production. At Factorial, being a Staff Engineer means leading technical initiatives and working very closely with Product, not operating at arm's length from the roadmap. You’ll be writing Rails and React, designing systems, and shipping product hand in hand with Product and Design. "AI" is the domain you’ll work in, not a different job.

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.

We’re 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 we’re building on top of that: agentic workflows, LLM-integrated features, systems that behave probabilistically rather than deterministically.

What are we looking for?

You have solid depth in both backend and frontend software engineering
You’ve shipped real products to production, not just prototypes or proofs of concept
You understand APIs, cloud platforms (AWS, Azure, or GCP), and system design well
You’ve integrated LLM APIs into product features and shipped them to real users. This is about building with AI, not training or fine‑tuning models
You’re seen as a technical and cultural leader, and you hold the bar high
You push back on process that doesn’t serve the team, from hiring to deployment
You drive adoption of new abstractions and make sure others can actually use them
You’ve shipped things that made a measurable difference, at work or on the side
You lead key technical decisions and create things others across the company build on
You communicate clearly in English; Spanish is a plus

What You’ll Be Doing?

Lead technical initiatives. As a Staff Engineer, you’ll set technical direction for meaningful chunks of the roadmap, not just execute against it. You’ll make the calls on architecture and approach, and be accountable for how they play out.
Work very closely with Product. This isn’t occasional collaboration, it’s a tight, ongoing partnership. You’ll shape what gets built alongside Product and Design from the earliest conversations, not just take specs and implement them.
Own systems end to end. From the first conversation about a problem, through production rollout, to long‑term maintenance. Including the unglamorous parts.
Stay close to customers. The best technical decisions come from understanding real problems, so you’ll talk to customers directly and bring that context back into how we build.
Help define how we build AI features at scale. We’re still figuring out what great AI product engineering looks like at Factorial, and that’s part of the job. You’ll help shape how we design, build, and run AI‑native product experiences so they’re reliable, compliant, and genuinely useful.
Champion spec‑driven development. Push for a culture where teams define what "good" looks like before they build: expected behaviors, constraints, edge cases, success criteria. Then use those specs to move fast without breaking things.
Build things other teams can reuse. Rather than a patchwork of one‑off AI experiments, you’ll build shared components other product domains can actually use: scalable, secure, and easy to govern.
Design and evolve AI Skills. Drive the creation of modular, reusable AI "skills" that automate real workflows and take safe, traceable actions inside Factorial’s ecosystem, especially where finance is involved.
Build the tooling that keeps AI features trustworthy. Getting an AI feature to production is one thing. Keeping it reliable once real customers depend on it is another. You’ll build monitoring and quality tooling (automated and human‑in‑the‑loop) so teams get a real signal on quality.
Ground AI features in data we actually trust. Help define how we combine LLM outputs with deterministic sources of truth, balancing flexibility with accuracy and compliance.
Raise the bar across the company: Whether it’s mentoring, hiring, or pushing for better practices, you’ll leave the engineering culture better than you found it

One honest note:

One honest note: if you’re mainly looking to do model training, fine‑tuning, or applied ML research, this probably isn’t the right role for you. We’re a product engineering team working with LLM APIs and agentic systems, not a team building models from scratch.

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. That’s 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 don’t 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

Intro Call &rightarrow; Chat with our Talent Partner about your journey and goals.
Hiring Manager Interview &rightarrow; Deep dive into your product mindset, teamwork, and problem-solving.
Live Challenge &rightarrow; A collaborative technical exercise based on real‑life problems.
Final Coffee Chat &rightarrow; 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

Factorial is the AI for Business that knows companies, connects how work happens across the business, and turns that context into action.

Founded in Barcelona in 2016, we now have +1,700 employees serving more than 16,000 companies across 112 countries.

Factorial started with a simple idea: companies were spending too much time managing processes and not enough time doing the work they were hired to do: their best work.

But as companies grow, work gets more disconnected. More people, more tools, more information, and more time spent connecting the dots. Generic AI can answer questions, but it doesn’t know your company. Every time, you have to give it the context.

Factorial is different. Because it’s inside the company, it already knows how it works, including its people, processes, policies, and data. So you can ask it to do real work, from screening candidates and managing expenses to answering questions and creating reports.

AI isn’t the goal. Giving people back their time is.

When work changes, so do we.

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: We’re 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