Jan-Marten Jongerius

An experienced programmer, compassionate mentor and driven problem solver. I'm the right kind of developer for challenging business solutions.

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Experience

Nov 2007 ‐ Present ‐ 17 yrs 7 mos

Testimonials

Recommended by peers 🌸

Jan-Marten is the best of both worlds. Highly skilled, technically flexible engineers that stay cool and creative under pressure are alone hard to come by. But match that with his deeply empathetic, communicative, up-lifting leadership? That is unicorn gold. JM’s decisions reflect not just what’s possible, but what’s principled. He builds high-trust, high-autonomy environments where engineers thrive. I would - and I will - hire him again and again, given the chance.

Jennifer Jaffe
Jennifer Jaffe
senior to me
May 29 2025

I had the pleasure of working with Jan-Marten at Slimmer, where he was my tech lead—and I couldn’t have asked for a better mentor and teammate.

Jan-Marten has a remarkable ability to stay calm and focused under pressure, guiding the team with a steady hand even in the most challenging situations. I learned a great deal from him—not just technically, but also in how to approach problems thoughtfully and collaboratively.

What I appreciate most is that Jan-Marten is never condescending when helping others. He’s approachable, always willing to lend a hand, and genuinely cares about the growth of those around him. His strong work ethic is inspiring, and he still manages to keep things fun and light-hearted.

I’m truly grateful to have worked with Jan-Marten and would gladly do so again. Anyone would be lucky to have him on their team.

Santhosh Rajamanickam
Santhosh Rajamanickam
reported directly to me
May 23 2025

I had the pleasure of working with Jan-Marten and witnessing his exceptional leadership skills firsthand. As a team leader, he consistently created a supportive and motivating environment where every team member felt valued and empowered. His ability to communicate clearly, make thoughtful decisions, and lead by example had a significant impact on our team's success.

Jan-Marten is someone truly dedicated to the success of the team, but what sets him apart is the genuine care he shows for each individual. While driving the team toward our goals, he also actively supports both the professional and personal development of every team member. He is always there to help, and never hesitates to offer support when it's needed.

Jan-Marten is an exceptional observer — often recognizing when something might be off, even before it's said out loud. Whether the issue is work-related or personal, he is the kind of leader who makes time to listen and provide meaningful help. His empathy, attentiveness, and ability to value people on a human level make him not just a great leader, but an inspiring one.

I truly hope I get the chance to work with him again in the future. Any team would be incredibly lucky to have such a thoughtful and dedicated leader. Thanks Jan-Marten 🌸

Esranur Galip Kayahan
Esranur Galip Kayahan
reported directly to me
May 22 2025

Jan-Marten is a very good senior engineer and architect. But even more impressive is his high EQ, empathy and ability to lead and coach a team to collective high performance! He is super dedicated to both the business/technical outcomes, as well his team. He doesn’t take shortcuts, but build software and the team for the long run.

JC Heyneke
JC Heyneke
managed me directly
May 22 2025

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The experienced developer you need

An experienced developer, with a broad set of skills, supporting your application, wherever and however it needs it most.

Academic mindset

With an academic mindset, eager to learn and focused on your domain.

Reverse engineering

The bridge between the end of documentation and the beginning of your application and domain.

Full-stack development

Sysops, Devops, CI/CD, Back-end, API and Front-end are all comfortably part of my vocabulary.

Leadership

Whether the project at hand needs steering, the team requires a renewed focus or by supporting personal growth.

Balanced approach

Great at finding the right balance between pragmatic solutions and investments in the longevity of the product.

Thorough, precise, safe

Delivered work meets agreed upon standards. Making sure the right work is deployed at the most opportune moment is part of the deal.

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Events

  • On top of the Elephpant

    Have you ever wondered how your code is being read and interpreted? Do you feel the urge to write your own language, but don't know where to start?

    This talk shows some of the basic concepts of programming languages. It gives pointers on where to start, resources to consume, design approaches to consider and a few pitfalls for the over confident.

  • WordPress Meetup Grunn oktober

    Communities stay in touch with PHP at their own pace. This talk focuses on highlighting the features found in PHP 7 and 7.1. It shows off their benefits and gives you ammo to start upgrading your codebase today.

  • Using PHP 7 in the wild

    Not all of us have the luxury of working with PHP 7 at our day jobs. Luckily, some of us do. This talk will show off pretty interesting benefits for the PHP developers and their managers. PHP 7 lets us do more with less and this talk will get you started in the right direction.

  • Comparing Frameworks

    What PHP Framework do you use? What are its strong points, and where is it less usefull? Analyze and share your experience in terms of the Jumbo Building Blocks of Jan-Marten Jongerius and Remko Silvis and hear what others think of the frameworks they used or tried!