Jacob Duijzer on Coffee-Driven Development

Event Sourcing with .NET and Marten

Fri, 12 Jun 2026 00:00:00 +0200

The year 2026 began with unusually heavy snowfall in the Netherlands. It was more than we are used to, and in some cases enough to cause buildings to collapse.

I work for an organization that provides Building Information Management services, so it made me think: what happens after a building collapses? There will probably be investigations into the specifications that were used at the time. Do we keep the full history? Do we know whether changes were made, why they were made, when they were made, and by whom?

I had already been looking for a reason to dive into event sourcing, and this felt like a useful example. Event sourcing is not only about storing the current state of something, but about storing the facts that led to that state. That makes it a good fit for systems where history matters.

In this post, I’ll use changing roof specifications as a small example to explain event sourcing, and show how it can be implemented in .NET with Marten.

Whole Team Collaboration: Navigating the seven C's

Fri, 12 Dec 2025 00:00:00 +0100

On November 27 and 28, I went to the XP Days Benelux conference. This blog post is a short recap of all the things I learned.

In this third post in the XP Days series, I’m sharing my notes and reflections from the session “Whole Team Collaboration: Navigating the Seven C’s” by Per Beining. There are many ways of working together, and many ways of not really working together. By introducing the Seven C’s (spoiler: there are actually eight), Per offered a simple but powerful lens to help teams recognise how they currently collaborate and what they might change to truly work together.

The goal of the session was to build awareness: understand the difference between merely working side by side and genuinely collaborating, and learn how to spot which “C” your team is currently navigating—so you can steer toward the harbour you actually want to reach.

DUO Portfolio Game

Thu, 11 Dec 2025 00:00:00 +0100

On November 27 and 28, I went to the XP Days Benelux conference. This blog post is a short recap of all the things I learned.

In this second post, I’m sharing my notes and reflections from the session “DUO Portfolio Game” by Jan-Willem Zijlstra, Jeroen Smit, and Willem Kleinenberg. The session introduced a game they developed to spark conversations about culture, collaboration, and ways of working. Through several rounds, participants experienced firsthand how different strategies for distributing work across teams can shape flow, ownership, and alignment.

The goal of the session was clear: explore how teams might organize and collaborate more effectively, and discover what happens when you shift constraints, responsibilities, or communication paths.

So long, and thanks for all the fish - The farewell tour

Wed, 03 Dec 2025 00:00:00 +0100

On November 27 and 28, I went to the XP Days Benelux conference. This blog post is a short recap of all the things I learned.

In this first post, I’m sharing my notes and reflections from the session “So Long, and thanks for all the fish - The farewell tour" by Ron Eringa, Paul Kuijten, and Dajo Breddels. The session explored the question of whether the Agile movement has run its course: been there, done that, got the T-shirt. With the Agile label losing some of its shine, the facilitators invited us to properly say goodbye to what no longer serves us, and to salvage the practices and principles still worth keeping.

The goal of the session was simple but important: take stock. Is Agile dead? And if not, how do we move forward?

An Astronaut's Guide to Life on Earth

Wed, 28 May 2025 00:00:00 +0200

Colonel Chris Hadfield has spent decades training as an astronaut and has logged nearly 4000 hours in space. During this time he has broken into a Space Station with a Swiss army knife, disposed of a live snake while piloting a plane, and been temporarily blinded while clinging to the exterior of an orbiting spacecraft. The secret to Col. Hadfield’s success-and survival-is an unconventional philosophy he learned at NASA: prepare for the worst-and enjoy every moment of it.

The Road to Faster Flow Is Paved with Missteps: A Retrospective

Sun, 04 May 2025 21:30:00 +0200

This is a recording of my talk at the Fast Flow Conf NL conference, on the 27th of March, 2025.

Two years ago, we set out on a journey to transition to a Team Topologies-inspired organization, aiming to unlock faster flow and better collaboration. Today, it’s time to reflect on the lessons learned along the way.

About Me

Thu, 01 May 2025 00:00:00 +0200

Hi, I’m Jacob Duijzer — a passionate engineering leader, speaker, and lifelong learner.

With a background in software development and a deep appreciation for well-designed systems, I help teams deliver better software through clarity, collaboration, and continuous improvement. I’m especially interested in how approaches like Behavior-Driven Development (BDD), Domain-Driven Design (DDD), and Team Topologies can transform the way we build software — and the teams behind it.

I enjoy sharing what I learn, whether it’s on stage at a conference, in a blog post, or during a team workshop. My talks often mix real-world experience with storytelling, practical insights, and the occasional book recommendation (or two).

Stop Copy-Pasting Your Resumé (and Everything Else)

Sat, 19 Apr 2025 00:00:00 +0200

You just got asked for an updated resumé. Again. So you open that folder—one in Google Drive, another buried in Downloads, and maybe another one in your email. There’s a version from three jobs ago, one you tweaked last year… and they’re all a mess.

But what if your resumé lived in source control? Versioned. Clean. Written in plain text. Ready to export to PDF in seconds.

That same approach works for more than just your own documents. When I’m hiring developers, I use AsciiDoc to generate technical assessments too—polished, structured PDFs without fiddling in Word. And once it’s generated, it’s automatically uploaded to the Confluence page for our hiring process, so recruiters and interviewers always get the latest version—without needing to ask.

In this post, I’ll show you how I use AsciiDoc to create reusable documents—like resumés, cover letters, and candidate assessments—that compile into beautiful, consistent PDFs in seconds. No CI/CD pipeline required - but you can absolutely add one later to automate PDF generation and publishing. Just structured content, a simple setup, and the joy of never formatting by hand again.

Testing GraphQL with Specifications: A Deep Dive with Reqnroll

Tue, 28 Jan 2025 00:00:00 +0000

GraphQL has been around since 2012, yet many developers haven’t had the chance to work with it. Personally, I’ve been using GraphQL on and off for several years, both in personal and professional projects. Recently, I’ve been diving deeper into it again—and I’ve fallen in love with it all over.

While implementing a few queries and mutations, I started to wonder: how could I effectively test my GraphQL implementation? Specifically, how could I send queries and mutations with a GraphQL client directly from my tests to ensure everything works as expected?

After some experimentation, I found a solution I’m excited to share: combining specifications with Reqnroll, the .NET WebApplicationFactory, and the Strawberry Shake GraphQL client to test a Hot Chocolate GraphQL server. This approach not only works seamlessly but also results in clean, readable specifications.

In this article, I’ll guide you through the process of setting up these tests, allowing you to test your own GraphQL server with clarity and confidence. Let’s get started!

DevOpsDays Eindhoven 2023

Mon, 16 Oct 2023 00:00:00 +0000

It was on my radar last year, but I decided not to go, but to go to Techorama instead. But, after hearing good stories about the first edition of the DevOpsDays Eindhoven, I decided to skip Techorama and go to the DevOpsDays Eindhoven 2023.

In this post, I will explain what the DevOpsDays are, and share some of my learnings. I hope you will enjoy it and, maybe, I might inspire you to join me next year!

Better Value Sooner Safer Happier, a review

Thu, 20 Apr 2023 00:00:00 +0000

Yesterday, I attended a session, presented by Jonathan Smart, on the topic of “Better Value Sooner Safer Happier” which was based on his book “Sooner Safer Happier”. The author’s approach is based on Lean, Agile, and DevOps principles, which have been adopted by many organizations worldwide, but with a strong focus on outcome, not on any process like Scrum, DevOps or Scaled Agile. In this review, I will share my key takeaways, I will not share his full talk, you can read the book and find some videos online.

Talks & Publications

Mon, 01 Jan 0001 00:00:00 +0000

Recordings

2025

The Road to Faster Flow Is Paved with Missteps: A Retrospective, Fast Flow Conf NL (2025-03-27)

Jacob Duijzer on Coffee-Driven Development

Event Sourcing with .NET and Marten

Whole Team Collaboration: Navigating the seven C's

DUO Portfolio Game

So long, and thanks for all the fish - The farewell tour

An Astronaut's Guide to Life on Earth

The Road to Faster Flow Is Paved with Missteps: A Retrospective

About Me

Stop Copy-Pasting Your Resumé (and Everything Else)

Testing GraphQL with Specifications: A Deep Dive with Reqnroll

DevOpsDays Eindhoven 2023

Better Value Sooner Safer Happier, a review

Talks & Publications

Recordings

2025

2024

2023

2022

Publications

Talks not recorded