Mermaid

Renders Mermaid diagrams directly in markdown using fenced code blocks. Supports the usual suspects: flowcharts, sequence diagrams, state machines, class diagrams, ER diagrams, Gantt charts, and mindmaps. The main gotcha is list syntax conflicts. If you write "[1. Item]" it'll break with an unsupported markdown error, so you need to remove the space after the period or use circled numbers instead. Documentation recommends using "flowchart" over "graph" and defaults to top-to-bottom layout. Honestly, this is just Mermaid wrapped as a skill, so if you already know the syntax you're good to go. The skill guide focuses heavily on those syntax traps, which is probably the most useful part.