Careers

Senior Full-Stack Developer

Written by Johan Theunissen | 16/07/2026

About Keeyns

We are a young and fast-growing company from ‘s-Hertogenbosch on a mission to revolutionise tax management. Our platform is helping notable international businesses stay on top of their tax compliance at low costs. We offer an intuitive solution that enables our customers and their external advisors to collaborate on tax filings, securely store documents and reduce repetitive, error-prone manual tasks. This all takes place in our easy-to-use web application, providing maximum control and auditability. 

Our culture is one of few rules but ambitious standards. These things matter to us:

  • We are a team of smart and driven people with a passion for technology.

  • We work hard and get shit done, but also play hard and have fun along the way.

  • We ask a lot of questions and are eager to learn.

  • We speak up, show initiative and listen to each other’s ideas.

  • We have a clear vision and can connect each individual’s work to the bigger picture.

  • We are inclusive, and diverse and offer equal opportunities for all.

 

Senior Full-Stack Developer at Keeyns

Code hard. Ship fast. Own everything.

As our Senior Full Stack Developer, you build scalable, production-ready software with .NET on the backend and React on the frontend. You move fast, think in systems, and own things end to end. You're comfortable in a fast-moving tax technology company where looking forward beats looking back.

 

 Mission

You don't just write code, you build systems that matter. You take ownership from concept to deployment, keep the quality bar high, and make sure the people around you grow along the way. You know your craft inside and out, and you can explain it clearly to anyone on the team.

 

 What You Bring

  • 5+ years building full stack applications that made it to production (and stayed there)
  • Deep expertise in .NET (C#) and React with 5+ years of hands-on React and TypeScript experience
  • Deep expertise in databases (SQL) and Azure cloud technologies
  • Bachelor-level education and a strong analytical mindset
  • Solid knowledge of Design Patterns and architectural principles. You can explain them clearly to a junior without making them feel lost.
  • A track record of PR reviews that are thorough, specific and constructive. You raise the bar, not just flag the issues.
  • Experience with CI/CD pipelines and Azure DevOps
  • Familiar with Scrum and Agile
  • A strong communicator who drives collaboration and knows when to push back

 

 What You’ll Do

  • Build end-to-end features (no silos, no handoffs)

  • Design and implement robust APIs and scalable backend services

  • Craft intuitive, high-performance components with React

  • Own performance, security, and reliability like it’s your product

  • Do code reviews that teach as much as they correct

  • Actively share knowledge and help your junior teammates grow in skill and confidence

  • Collaborate with product and design, but challenge them when needed

  • Continuously improve the stack, tooling, and engineering standards

 Your DNA

  • You know why the system is built the way it is, not just how

  • You question assumptions and kill complexity

  • You prefer working software over endless meetings

  • You take responsibility when things break (because they will…) 

  • You mentor without ego and you know how to make things click for people

  • Your PR reviews move the code and the team forward

  • You make the whole team better just by being on it

 Stack Snapshot

  • Backend: .NET, Entity Framework

  • Frontend: React, TypeScript, Modern State Management

  • Cloud: Azure (App Services, Functions, DevOps)

  • Data: SQL Server

  • Tooling: Git, CI/CD

What we Offer

You'll have real ownership, not just responsibilities on paper. No endless layers, no bureaucracy, just building impactful software with people who care about quality and speed.
We also offer a competitive package consisting of a salary befitting your experience and good employment conditions.

If you're looking for a place to hide behind tickets, this isn't it. But if you want to build, own, and push boundaries, then we’d love to meet you! Apply using the form below or get in touch with me (Johan Theunissen - johan@keeyns.com)