Full Stack Engineer

Madrid | ZKO – Product & Technology | Full time | Hybrid

Our Client

They're building the back-office of the future for millions of small businesses: accounting, taxes, payroll, financing (all powered by cutting-edge AI and a team of advisors who truly understand what matters to clients). They're early. They move fast. And they're looking for someone who thrives in that environment, not despite it.

Your mission

Your job isn't just to write code, it's to solve problems. That means asking the hard questions before touching a keyboard, understanding the why behind every request, cutting scope ruthlessly when needed, and shipping things that actually move the needle. You'll work across the full stack, back-end services, front-end dashboards, automations, AI pipelines; and you'll own features end-to-end (from understanding the problem, to scoping the solution, to deploying and iterating). They want someone who questions before building, and knows when the best solution is a simpler one.

What you'll do

• Own problems, not just tickets: you'll push back when something isn't worth building, and move fast when it is.
• Build and maintain back-end services in Python (FastAPI, Pydantic), with a strong focus on reliability and maintainability.
• Design and automate complex workflows: document processing, email handling, third-party API integrations and OCR (using tools like n8n, LangChain, MCP, and similar).
• Build front-end interfaces: dashboards, internal tools, chat experiences that are fast, clear, and genuinely useful (React).
• Own deployment and monitoring end-to-end.

What they're looking for

• Solid production experience with Python (FastAPI, Pydantic, Pandas) and JavaScript/TypeScript (React or similar), you've shipped real things that real people use.
• Comfortable owning both front-end and back-end without needing to split the work.
• Experience with deployment, infrastructure, and monitoring, you don't throw things over the wall.
• Strong product instinct: you think about users and outcomes, not just systems and tasks.
• Intellectual honesty: you push back on bad ideas (including your own), and you'd rather solve the right problem simply than the wrong one perfectly.
• At ease with ambiguity: you can go from a vague problem to a shipped solution without someone holding your hand every step of the way.

How they work

• Real problem, real users: You won't be building in a vacuum. You'll work closely with the accountants, advisors, and small business owners who use what you ship.
• Flexibility & hybrid work: They believe in ownership and responsibility over schedules. They trust people to manage their time and deliver results.
• Tools & setup: AI-first tools and workflows, latest-generation hardware, and everything you need to work faster and better.
• Growth & development: You'll have a dedicated training budget. They're clear about where they are and where they're going as a company, and you'll have periodic performance reviews to support your development and career progression.
• Compensation: They believe in a meritocratic culture. They also offer flexible compensation (transport, restaurants, and other benefits).