# Uml Diagrams

> Create and validate diagrams with the uml-mcp MCP server (generate_uml, generate_uml_image, validate_uml, list_diagram_types, generate_uml_batch). Use for UML, Mermaid, D2, Graphviz, Kroki URLs, inline chat images, goat/umlet, or diagram_type questions.

- Skill: `antoinebou12/uml-diagrams` (Agent Skill)
- Install (CLI): `npx skillmds@latest add antoinebou12/uml-diagrams`
- Raw SKILL.md: https://api.skillmd.com/api/skills/antoinebou12/uml-diagrams/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: antoinebou12 (https://skillmd.com/u/antoinebou12)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/antoinebou12/uml-diagrams

---


> **Maintainers:** Canonical long-form copy also lives in [`.skill/skills/uml-mcp-diagrams/SKILL.md`](https://github.com/antoinebou12/uml-mcp/blob/main/.skill/skills/uml-mcp-diagrams/SKILL.md). Keep tool tables and `output_dir` wording aligned with the Smithery bundle [uml-skill](https://github.com/antoinebou12/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](url).

## 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

| Field | Notes |
| --- | --- |
| `diagram_type` | Required; must match server-supported keys. |
| `code` | Required; DSL only. |
| `output_dir` | Omit for HTTP MCP (URL + base64 when not URL-only). |
| `output_format` | Often `svg`; use `png` for chat ImageContent. Check **`uml://formats`**. |
| `theme` | PlantUML types only. |
| `scale` | SVG only. |

## 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:

```markdown
![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

| Intent | Typical `diagram_type` |
| --- | --- |
| Classes / associations | `class` or Mermaid `classDiagram` |
| Lifelines / messages | `sequence` or Mermaid sequence |
| Flow / BPMN | `activity`, `bpmn`, or Mermaid flowchart |
| Quick charts | `mermaid` |
| Declarative layout | `d2` |
| ASCII art → SVG | `goat` or `svgbob` |
| UMLet UXF | `umlet` |

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