PlantUML vs Whimsical MCP

PlantUML

One Java command reads diagram text from stdin and writes PNG, SVG, PDF or ASCII with no account, and CI passed on the last eight pushes. The default security profile lets diagram text read any local file and fetch any URL, and the documentation still lists chronology diagrams that release 1.2026.2 switched off.

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.

PlantUML

1. Set PLANTUML_SECURITY_PROFILE to SANDBOX or ALLOWLIST before rendering text from an untrusted source. The default profile lets !include read local files and fetch URLs
2. Run java -jar plantuml.jar --check-syntax with -stdrpt first and read the exit status. Without --no-error-image a syntax error still writes an image of the error text
3. Pass -pipe with --svg, --txt or --utxt to work without files. --txt output suits a text-only model
4. Start the local server as -picoweb:8080:127.0.0.1. Without the bind address it listens on every interface
5. Use npx -y @plantuml/mcp-js when no Java runtime is present. It renders SVG only, so use the jar for PNG or PDF

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