Senior Fullstack Engineer - AI-Powered Platform Builder

Experis España; Barcelona; On-site; EUR 70,000 - 95,000; Full time

Job summary

Experis, a ManpowerGroup company, seeks a Senior Software Engineer to join Kompanion as a core early member in Engineering. You will build the foundations of an AI-native platform for critical tax, accounting, and financial workflows, owning features end to end and shaping product and engineering standards.

You’ll work with Java, Spring Boot, Next.js, and PostgreSQL, contributing across backend and platform-level concerns while collaborating with Tax, Accounting, Growth, and Operations teams.

Qualifications

• 5+ years of experience building and operating production software.
• Strong backend engineering experience.
• Proficiency in Java and Spring Boot.
• Solid PostgreSQL knowledge and data modelling.
• 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 ability to turn ambiguous problems into shipped products.

Responsibilities

• 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.

Skills

Backend development

Java

Spring Boot

PostgreSQL

React/Next.js

Production ownership

System design

Testing

Security

Education

Computer Science / Software Engineering degree welcome

Job description

Experis, a ManpowerGroup company, seeks a Senior Software Engineer to join Kompanion as a core early member in Engineering. You will build the foundations of an AI-native platform for critical tax, accounting, and financial workflows, owning features end to end and shaping product and engineering standards.

You’ll work with Java, Spring Boot, Next.js, and PostgreSQL, contributing across backend and platform-level concerns while collaborating with Tax, Accounting, Growth, and Operations teams.