Uml Diagrams

Maintainers: Canonical long-form copy also lives in .skill/skills/uml-mcp-diagrams/SKILL.md. Keep tool tables and output_dir wording aligned with the Smithery bundle uml-skill.

UML-MCP in Claude Code

Goal

Produce valid diagram_type and DSL code, call generate_uml (or generate_uml_image to show a picture in chat), and give the user the url (and playground when present). Prefer URL-first output: omit output_dir / use null unless the user wants files on disk (local stdio only).

Do

• If diagram_type is unclear, use list_diagram_types or read uml://types / uml://formats before generate_uml (~37 types, including goat and umlet).
• Match diagram_type to the language of code (e.g. Mermaid body → mermaid; @startuml → plantuml or the specific Kroki PlantUML subtype when applicable).
• Use validate_uml before heavy retry loops or on pasted diagram source; use strict: true for Mermaid sequences.
• Mermaid sequenceDiagram: one statement per line — do not pack with ; on a single line.
• For inline chat images, call generate_uml_image with png (fetches bytes even when hosted MCP_URL_ONLY is on). generate_uml with png/jpeg also force-fetches; SVG replies include a markdown image URL in the tool text.
• Return the url, playground (as a markdown link when present), and a short copy of code.
• Do not link local output/*.png paths in chat; use MCP image content or the HTTPS URL.

Do not

• Invent diagram_type or output_format; confirm from uml://types / uml://formats or list_diagram_types.
• Put prose inside code—only valid diagram DSL.
• Set output_dir unless the user asked for saved files (not applicable to the default HTTP deployment).
• Pack Mermaid sequence statements with ; on one physical line.
• Omit playground when the tool returned it — always surface it as Playground: open editor.

Before generating

1. Read uml://types / uml://capabilities when the type is ambiguous.
2. Use uml://templates, uml://examples, or uml://recipes for starters.
3. Optional: validate_uml with strict: true for stricter Mermaid/D2 checks.

Tools and resources

• Tools: generate_uml, generate_uml_image, validate_uml, list_diagram_types, generate_uml_batch
• Resources: uml://types, uml://formats, uml://templates, uml://examples, uml://capabilities, uml://recipes, uml://server-info, uml://workflow, plus URIs from resources/list

Prompts (when exposed): uml_diagram, uml_diagram_with_thinking, class_diagram, sequence_diagram, activity_diagram, usecase_diagram, mermaid_sequence_api, mermaid_gantt, bpmn_process_guide, c4_model, wireviz_harness, bpmn_executable_process, convert_class_to_mermaid, algorithm_explainer, paper_concept_diagram.

generate_uml inputs

generate_uml_image

Same diagram fields as generate_uml; default png. Use when the user wants the diagram visible in chat. On Vercel / MCP_URL_ONLY, this tool still force-fetches image bytes for MCP ImageContent.

generate_uml_batch

Bounded concurrency (MCP_BATCH_CONCURRENCY, default 4). Mermaid-majority batches are capped at 2 workers on the server. Recover failed Mermaid items with solo generate_uml.

After generation

Present this shape every time:

![diagram](<url>)

- **URL:** <url>
- **Playground:** <playground>

\`\`\`mermaid
<code>
\`\`\`

Copy url / playground only from the MCP tool result. On error, fix DSL or types and retry or run validate_uml. Smoke prompt: tests/prompts/chatgpt_mcp_smoke_test.md.

Intent → type hints

When several fit, prefer what the user named; otherwise prefer the clearest match from uml://types.