What leaves your Jira site
Rendering encodes or posts the source to client.api.app.<zone>/v1/diagram with your token attached. Nothing in the Jira edition lets an admin turn this off, because there is no settings screen.
#What it does
Diagram source for text-based languages is sent to Capable's hosted rendering service. Draw.io, Excalidraw, BPMN and DMN never leave the browser.
#Related
Better with company.
