Kroki vs Lucid API + MCP

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.

Lucid API + MCP

OAuth 2.0 scopes with :readonly variants, and audit log endpoints in the REST API. No public changelog for the API or the MCP server.

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

Lucid API + MCP

1. Always send Lucid-Api-Version: 1, or prefix the path with /v1
2. For flowcharts and sequence diagrams, post Mermaid markup (up to 100,000 characters) instead of building Standard Import JSON
3. Request :readonly scopes when the agent only reads documents
4. On 429, wait 60 seconds or back off. Create Mermaid Diagram allows 60 calls a minute
5. Sharing and embed endpoints need an OAuth token. An API key won't work there