At Experis, a ManpowerGroup company, we specialise in recruiting the best tech talent and matching them with all kinds of organisations, from large corporations to start-ups. We are a company specialising in IT consultancy and the recruitment of professionals in the technology sector across our three practice areas: Business Transformation, Cloud & Infrastructure, and Enterprise Applications. We have a workforce of over 1,800 IT specialists in Spain and an international presence in 54 countries. If you’re a technology professional, we’d love to help you find that new opportunity you’re looking for – the one that will propel you to the next level in your career. Find your next opportunity with us. Take your career to the next level with Experis.

About the Opportunity We’re looking for a Senior Software Engineer to join Kompanion as the third person in Engineering and one of the first eight employees in the company.

You’ll help build the foundations of a robust, AI-native platform for critical tax, accounting, and financial workflows. This is a hands-on role with broad ownership. You’ll lead features end to end, work closely with Tax, Accounting, Growth, and Operations, and help shape our product, engineering standards, hiring, and technical culture. Our stack and initial architecture are in place. Most of what comes next is still open to influence.

How We Build Our stack includes Java, Spring Boot, Next.js, and PostgreSQL.

Engineering owns almost the full product loop: refining problems, researching the domain, writing PRDs, designing solutions, building, shipping, and validating them.

We use AI across development and inside the product, from document processing and assistants to autonomous agents.

We move fast where we can and carefully where reliability, security, and compliance matter. We avoid unnecessary architecture, excessive meetings,



and working from tickets without understanding the problem.

What You’ll Be Doing

Owning features end to end, from problem definition to production and validation

Building across the stack, with a stronger focus on backend systems and business logic

Operating the platform in production and improving its reliability, performance, observability, and security

Working closely with Tax, Accounting, Growth, and Operations

Building integrations, automations, internal tools, and AI-powered features

Improving our architecture, developer experience, testing, and engineering standards

Reviewing code, mentoring engineers, and participating in hiring

What You’ll Need

5+ years of experience building and operating production software

Strong backend engineering experience

Experience with Java and Spring Boot, or the ability to become productive with them quickly

Solid PostgreSQL knowledge, including data modelling and query performance

The ability to work with React or Next.js when needed

Experience owning systems in production

Strong fundamentals in clean code, testing, security, and system design

High autonomy and the ability to turn ambiguous problems into shipped products

A degree in Computer Science, Software Engineering, or a related field is welcome, but not required.

Nice to Have

Experience building regulated, auditable, or high-stakes software

Experience designing a platform from its early stages

Experience with security, privacy, or sensitive financial data

Experience with event-driven or asynchronous systems

Experience building AI-powered products or using AI-assisted development tools

Previous early-stage startup experience

Who You Are

You’re a hands-on, low-ego engineer who wants to build. You balance speed with rigor, challenge decisions constructively, and seek the source of truth. You care about outcomes, communicate clearly, and help others improve.

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📌 Fullstack developer (Madrid)
🏢 Experis
📍 Madrid