For those who, like me, read this and thought "what the hell is a mermaid diagram?", apparently it is a method to describe simple flow diagrams using markdown-like text. More here: https://mermaid.js.org/
I've even found sonnet and opus to be quite capable of generating json describing nodes and edges. I had them generate directed acyclic processing graphs for a GUI LLM data flow editor that I built (also with Claude - https://nodecul.es/ if curious)