excalidraw

Produce and edit .excalidraw files — a flat scene of elements (rectangles, text, arrows) on an infinite canvas. Two ways to author, picked by scale:

• By hand (JSON) — for a handful of boxes, or editing an existing scene (recolor, rename, re-wire, append). The element format and binding/grouping rules below are what you need — and they're also what the programmatic path emits, so read them either way.
• Programmatically — for anything bigger or that you'll maintain. The toolchain in scripts/ builds scenes with Excalidraw's own convertToExcalidrawElements (it owns the gotchas: reciprocal binding, container labels, text sizing, z-order), renders a faithful SVG preview with exportToSvg, and lints geometry. See Programmatic authoring below.