ExcaliClaw vs Kroki

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.

Kroki

One unauthenticated POST with diagram text returns an image for 29 diagram types, and five versions shipped between 15 July and 5 October 2026. Four advisories were published in July and August 2026, one an unauthenticated remote code execution on /tikz/svg, all fixed. No OpenAPI file exists, and the public instance has no terms, privacy policy or status page.

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

Kroki

1. Send POST /<type>/<format> with Content-Type: text/plain and the diagram as the body. This avoids the deflate and base64 encoding that GET needs
2. Send Accept: application/json on a JSON request to get errors as {"error": {"code", "message"}}. With an SVG Accept header the error arrives as an image
3. Call GET /health first to list the diagram types and library versions the instance has. Mermaid, BPMN, Excalidraw and diagrams.net need companion containers
4. Run 0.32.1 or later before rendering untrusted text. Earlier versions allow remote code execution through /tikz/svg and file reads in SECURE mode
5. Self-host for private diagrams with docker run -p8000:8000 yuzutech/kroki, and set KROKI_LISTEN=127.0.0.1:8000 or a network rule, since the server has no authentication