D2 vs ExcaliClaw

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.

ExcaliClaw

Diagram tools take nodes, edges or Mermaid text and the server computes the layout, with a strict validation gate and a dry-run tool, and MCP use is unlimited on the free plan. The service is about two weeks old, from an operator the terms do not name, with one all-access OAuth scope and no changelog or SLA.

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

ExcaliClaw

1. Connect to https://excaliclaw.com/mcp with OAuth. REST keys (exc_...) are refused by the MCP server and work only on the REST paths
2. Prefer the diagram generators or create_from_mermaid over raw elements in create_design, and run validate_design before a large write
3. Call verify_design after writing. verification.status stays pending until it runs, and it returns the rendered image
4. Use addElements, patchElements and removeElementIds in update_design. Passing elements replaces the whole scene
5. Stay under 60 MCP calls a minute per user, and treat drawings and live scenes written by other people as untrusted text