I Built an Open-Source Mermaid Plugin for IntelliJ — Here's Why and What I Learned

If you use Mermaid diagrams in JetBrains IDEs, you've probably noticed the official plugin hasn't kept up. Architecture diagrams, kanban boards, treemaps — a good chunk of the newer diagram types either render poorly or not at all. I ran into this problem in my own workflow. I use Mermaid a lot for technical documentation, and I had some of my diagrams broken in the Markdown preview. So instead of waiting for a fix that wasn't coming, I built my own plugin. Six weeks later, Mermaid Visualizer is on the JetBrains Marketplace at v1.4.0, open-source under Apache 2.0. Why build yet another plugin? I was looking for a concrete project to learn the IntelliJ plugin ecosystem from scratch. I had never built a plugin before, never touched JCEF, never published anything on the JetBrains Marketplace. Rather than building a throwaway exercise, I picked a real problem I was facing every day. The existing landscape looked like this: The official JetBrains Mermaid plugin — closed-source, not fully fu