Disclosure up front: I'm affiliated with diagram.now — I'm connected to the product. I'm posting this to get developer feedback on diagram import/export interoperability, not to pitch an install.
Most teams I've worked with don't have one source of truth for their diagrams. They have:
a few Mermaid blocks living in READMEs and Markdown docs,
an old Visio (.vsdx) or Lucidchart file someone made two reorgs ago,
a SQL schema that is secretly the "real" ERD,






