LH Mermaid lets you put diagrams written in Mermaid syntax (flowcharts, sequence diagrams, entity-relationship diagrams, Gantt charts and more) into any post, page or presentation. The diagram is stored as plain text in the post, so it is versioned by revisions, readable in feeds and email, and easy for people and AI agents to write and edit; the bundled Mermaid library turns it into a drawing in the browser.
It adds one block, Mermaid Diagram, and is also shared infrastructure: other plugins (the Schema Diagram block in LH Schema Tools, Mermaid support in LH Presentations) use its copy of the library instead of bundling their own. Mermaid is only ever loaded on a request that actually draws a diagram.