creating-mermaid-diagrams

Category: Testing & Security | Uploader: Agents365-ai | Downloads: 0 | Version: v1.0（Latest）

Generate Mermaid diagrams (.mmd) and export to PNG/SVG/PDF using mmdc CLI or Kroki API. USE THIS SKILL when user mentions diagram, flowchart, sequence diagram, class diagram, ER diagram, state machine, architecture, visualize, git graph, 画图, 架构图, 流程图, 时序图. PROACTIVELY USE when explaining ANY system with 3+ components, API flows, authentication sequences, class hierarchies, database schemas, or state machines. Supports 11+ diagram types with fully automatic layout.

Changelog: Source: GitHub https://github.com/Agents365-ai/mermaid-skill

Directory Structure

Current level: Root

📁 assets/
- 📄 example.mmd 615 B
- 📄 example.png 62.8 KB
- 📄 workflow.mmd 900 B
- 📄 workflow.png 47.4 KB
- 📄 workflow_cn.mmd 910 B
- 📄 workflow_cn.png 46.7 KB
📁 reference/
- 📄 CLASS-ER.md 2.0 KB
- 📄 FLOWCHART.md 1.5 KB
- 📄 OTHER-TYPES.md 1.8 KB
- 📄 SEQUENCE.md 1.6 KB
📄 README.md 6.9 KB
📄 README_CN.md 6.7 KB
📄 SKILL.md 6.1 KB

SKILL.md

---
name: creating-mermaid-diagrams
description: Generate Mermaid diagrams (.mmd) and export to PNG/SVG/PDF using mmdc CLI or Kroki API. USE THIS SKILL when user mentions diagram, flowchart, sequence diagram, class diagram, ER diagram, state machine, architecture, visualize, git graph, 画图, 架构图, 流程图, 时序图. PROACTIVELY USE when explaining ANY system with 3+ components, API flows, authentication sequences, class hierarchies, database schemas, or state machines. Supports 11+ diagram types with fully automatic layout.
---

# Mermaid Diagrams

Generate `.mmd` text files and export to PNG/SVG/PDF using `mmdc` (local) or Kroki API (no install).

**Key advantage:** Text-based syntax with **fully automatic layout** — no x/y coordinates needed.

## Prerequisites

**Option A: Local (mmdc)**
```bash
npm install -g @mermaid-js/mermaid-cli
mmdc --version
```

**Option B: Kroki API (no install)**
```bash
curl --version  # Just need curl
```

## Workflow

1. **Check deps** — try `mmdc --version`, fallback to Kroki if unavailable
2. **Pick diagram type** — choose from table below
3. **Generate** — write `.mmd` file to disk
4. **Validate** — run validation (REQUIRED before export)
5. **Export** — use `mmdc` or Kroki API to produce PNG/SVG/PDF
6. **Report** — tell user the output file paths

## Validation (Required)

**NEVER export a diagram without validating first.**

```bash
# Validate with mmdc (local)
mmdc -i diagram.mmd -o /tmp/test.png 2>&1

# Validate with Kroki (if mmdc unavailable)
curl -s -X POST -H "Content-Type: text/plain" --data-binary @diagram.mmd https://kroki.io/mermaid/svg -o /tmp/test.svg && echo "Valid" || echo "Invalid"

# If error, fix the .mmd file and validate again
# Only proceed to export after validation passes
```

Common validation errors:
- Missing quotes around labels with special characters
- Wrong arrow syntax (use `->>` for sequence, `-->` for flowchart)
- Undeclared participants in sequence diagrams

## Diagram Types

| Type | Keyword | Use for |
|------|---------|---------|
| Flowchart | `flowchart TD/LR` | processes, pipelines, decisions |
| Sequence | `sequenceDiagram` | API calls, message passing |
| Class | `classDiagram` | OOP models, data structures |
| ER | `erDiagram` | database schemas |
| State | `stateDiagram-v2` | state machines, lifecycle |
| Gantt | `gantt` | project timelines |
| Pie | `pie` | proportions |
| Git Graph | `gitGraph` | branch strategies |
| C4 Context | `C4Context` | high-level architecture |
| Mind Map | `mindmap` | topic breakdowns |

## Syntax Reference

**Flowchart**: See [reference/FLOWCHART.md](reference/FLOWCHART.md)
**Sequence**: See [reference/SEQUENCE.md](reference/SEQUENCE.md)
**Class & ER**: See [reference/CLASS-ER.md](reference/CLASS-ER.md)
**Other types**: See [reference/OTHER-TYPES.md](reference/OTHER-TYPES.md)

## Examples

### Example 1: API Authentication Flow

**User prompt:**
> Create a sequence diagram for JWT authentication

**Generated `.mmd`:**
```mermaid
sequenceDiagram
  participant C as Client
  participant G as API Gateway
  participant A as Auth Service
  participant D as Database

  C->>G: POST /login {email, password}
  G->>A: validate(credentials)
  A->>D: SELECT user WHERE email=?
  D-->>A: user record
  A-->>A: verify password hash
  A-->>G: 200 OK + JWT token
  G-->>C: {token: "eyJhbG..."}
```

**Output files:** `auth-flow.mmd` + `auth-flow.png`

---

### Example 2: Microservices Architecture

**User prompt:**
> Draw an e-commerce microservices architecture

**Generated `.mmd`:**
```mermaid
flowchart TD
  subgraph Clients
    M[Mobile App]
    W[Web App]
  end

  GW[API Gateway]

  subgraph Services
    US[User Service]
    OS[Order Service]
    PS[Product Service]
    PAY[Payment Service]
  end

  subgraph Data
    UDB[(User DB)]
    ODB[(Order DB)]
    PDB[(Product DB)]
    REDIS[(Redis Cache)]
  end

  M & W --> GW
  GW --> US & OS & PS & PAY
  US --> UDB
  OS --> ODB
  PS --> PDB
  PAY --> REDIS
```

**Output files:** `ecommerce-arch.mmd` + `ecommerce-arch.png`

---

### Example 3: Order State Machine

**User prompt:**
> Show order lifecycle states

**Generated `.mmd`:**
```mermaid
stateDiagram-v2
  [*] --> Pending : order created
  Pending --> Confirmed : payment success
  Pending --> Cancelled : timeout/cancel
  Confirmed --> Shipped : dispatched
  Shipped --> Delivered : received
  Delivered --> [*]
  Cancelled --> [*]
```

**Output files:** `order-states.mmd` + `order-states.png`

## Export Commands

### Option 1: Local Export (mmdc)

Requires `mmdc` installed locally. Best for offline use.

```bash
# PNG (recommended: 2048px wide, white background)
mmdc -i diagram.mmd -o diagram.png -w 2048 --backgroundColor white

# PNG with theme (default | dark | neutral | forest | base)
mmdc -i diagram.mmd -o diagram.png -w 2048 --backgroundColor white --theme neutral

# SVG
mmdc -i diagram.mmd -o diagram.svg

# PDF
mmdc -i diagram.mmd -o diagram.pdf
```

### Option 2: Kroki API (No Install Required)

Use [Kroki](https://kroki.io) when `mmdc` is not available. No local dependencies needed.

```bash
# SVG via Kroki
curl -X POST -H "Content-Type: text/plain" --data-binary @diagram.mmd https://kroki.io/mermaid/svg -o diagram.svg

# PNG via Kroki
curl -X POST -H "Content-Type: text/plain" --data-binary @diagram.mmd https://kroki.io/mermaid/png -o diagram.png

# PDF via Kroki
curl -X POST -H "Content-Type: text/plain" --data-binary @diagram.mmd https://kroki.io/mermaid/pdf -o diagram.pdf
```

**Kroki advantages:**
- No local installation required
- Works on any system with `curl`
- Supports 20+ diagram types (PlantUML, GraphViz, D2, etc.)

**When to use Kroki:**
- `mmdc` installation fails
- Quick one-off diagrams
- CI/CD pipelines without Node.js

## Common Mistakes

| Mistake | Fix |
|---------|-----|
| `mmdc` not found | `npm install -g @mermaid-js/mermaid-cli` |
| Wrong arrow in sequence | Use `->>` for request, `-->>` for response |
| Special chars in label | Wrap in quotes: `A["Label: value"]` |
| Blank/small output | Add `-w 2048` flag |
| Participant order wrong | Declare `participant` explicitly at top |
| Subgraph name with spaces | Wrap in quotes: `subgraph "My Layer"` |

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creating-mermaid-diagrams

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SKILL.md

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