D2 vs Whimsical MCP

D2

A single local command turns text into a diagram in six formats with no account, key or network call, and CI passes on the default branch. The language is at 0.9.0 with no stable release, its company sponsor has shut down, and one maintainer with limited time wrote every commit since July.

Whimsical MCP

OAuth 2.1 with PKCE and separate read and write scopes. No API keys, so it can't run headless or in CI.

D2

1. Check the exit status of d2, never the output file. The man page says a partial render can be written when an error occurs
2. Run d2 validate file.d2 before rendering, and d2 fmt to normalise the source
3. Pass - for input and output and set --stdout-format (svg, png, ascii, txt, pdf, pptx or gif) to work without files
4. Use --stdout-format ascii when the reader is a text-only model
5. Pass --bundle=false or review image URLs and imports before rendering D2 text from an untrusted source. Release 0.9.0 fetches remote images when bundling

Whimsical MCP

1. Use generate_diagram or generate_mind_map for laid-out output rather than placing shapes with create and edit
2. Call how_to for Whimsical's syntax before writing a large diagram
3. Use fetch when you need a PNG snapshot of a board
4. delete removes files or objects without asking. Confirm with the person first