creating-mermaid-diagrams

---

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. homepage: https://github.com/Agents365-ai/creating-mermaid-diagrams metadata: {"openclaw":{"requires":{"bins":["curl"]},"emoji":"📊"}}

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)

npm install -g @mermaid-js/mermaid-cli
mmdc --version

Option B: Kroki API (no install)

curl --version  # Just need curl

Workflow

0. Update check (notify, don't pull) — first use per conversation. Throttle to once per 24 h via <this-skill-dir>/.last_update; never mutate the skill directory without explicit user consent.

   • If .last_update exists and is <24 h old, skip this step entirely.

   • Otherwise, fetch the latest tag from upstream:

     git -C <this-skill-dir> ls-remote --tags origin 'v*' 2>/dev/null \
       | awk '{print $2}' | sed 's|refs/tags/||' | sort -V | tail -1
     

   • Compare with this skill's metadata.version from the frontmatter. If the upstream tag is strictly newer (semver), tell the user one line and ask:

     "A newer version of this skill is available: vX.Y.Z → vA.B.C. Want me to git pull?"

     If they say yes, run git -C <this-skill-dir> pull --ff-only. Refresh .last_update either way so the prompt doesn't repeat for 24 hours.

   • If upstream is the same or older, refresh .last_update silently and continue.

   • On any failure (offline, not a git checkout — e.g. ClawHub-installed copy, read-only path, no permission), swallow the error silently and continue with the user's task. Do not mention the failure.

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.

# 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 Sequence: See reference/SEQUENCE.md Class & ER: See reference/CLASS-ER.md Other types: See reference/OTHER-TYPES.md

Examples

Example 1: API Authentication Flow

User prompt:

Create a sequence diagram for JWT authentication

Generated .mmd:

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:

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:

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.

# 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 when mmdc is not available. No local dependencies needed.

# 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"