mermaid

name	mermaid
description	Create, validate, and troubleshoot Mermaid.js diagrams. Use when generating flowcharts, sequence diagrams, class diagrams, ER diagrams, Gantt charts, state diagrams, or any other Mermaid visualization. Automatically validates syntax and fixes errors.
allowed-tools	Bash, Read, Write, Edit

Mermaid Diagrams Skill

This skill enables you to create valid, well-formed Mermaid.js diagrams with automatic validation using the validate_mermaid.sh (Linux/Bash) or validate_mermaid.ps1 (Windows/PowerShell) scripts.

Creating Diagrams

When asked to create a Mermaid diagram:

1. Reference the cheat sheet: Consult reference.md for syntax examples

2. Choose the right diagram type based on the use case:

   • Flowcharts: Process flows, decision trees
   • Sequence diagrams: API interactions, message flows
   • Class diagrams: Object relationships, system architecture
   • ER diagrams: Database schemas, data models
   • State diagrams: State machines, workflow states
   • Gantt charts: Project timelines, schedules
   • Git graphs: Branch strategies, commit history

3. Create the diagram following proper syntax:

   • Start with the correct diagram type declaration
   • Use consistent indentation
   • Quote labels with spaces or special characters
   • Follow arrow conventions for the diagram type

4. Always validate before finalizing (see validation section)

Validation Process

CRITICAL: Every Mermaid diagram MUST be validated before being considered complete.

Use the validate_mermaid.sh (Bash) or validate_mermaid.ps1 (PowerShell) script for all validation tasks. The script supports:

• Single diagram strings via stdin/pipeline
• Single diagram files (.mmd)
• Markdown files with embedded diagrams (.md)

Validation Methods

Method 1: Validate diagram from stdin (recommended for inline diagrams)

echo 'flowchart TD
    A --> B' | base/skills/mermaid/scripts/validate_mermaid.sh

Or using heredoc:

base/skills/mermaid/scripts/validate_mermaid.sh <<'EOF'
flowchart TD
    A --> B
    B --> C
EOF

Method 2: Validate single diagram file

base/skills/mermaid/scripts/validate_mermaid.sh /path/to/diagram.mmd

Method 3: Validate all diagrams in markdown file

base/skills/mermaid/scripts/validate_mermaid.sh /path/to/document.md

Validation Methods (Windows / PowerShell)

Method 1: Validate diagram from pipeline (recommended for inline diagrams)

$diagram = @"
flowchart TD
    A --> B
"@
$diagram | base/skills/mermaid/scripts/validate_mermaid.ps1

Method 2: Validate single diagram file

base/skills/mermaid/scripts/validate_mermaid.ps1 -FilePath "D:\path\to\diagram.mmd"

Method 3: Validate all diagrams in markdown file

base/skills/mermaid/scripts/validate_mermaid.ps1 "D:\path\to\document.md"

Interpreting Validation Results

Success:

✅ Diagram stdin: Valid

Failure with error details:

❌ Diagram stdin: Invalid
Error: Parse error on line 2:
...

Common Validation Issues & Fixes

When validation fails, the script will display the error. Check for these common issues:

Issue 1: Invalid Arrow Syntax

# WRONG
A <-!-> B

# CORRECT
A <--> B

Issue 2: Missing Line Breaks

# WRONG (all on one line)
sequenceDiagram Alice->>Bob: Hi Bob->>Alice: Hi Alice

# CORRECT (proper line breaks)
sequenceDiagram
    Alice->>Bob: Hi
    Bob->>Alice: Hi Alice

Issue 3: Unquoted Labels with Special Characters

# WRONG
flowchart LR
    A[Node with "unescaped quotes]

# CORRECT
flowchart LR
    A["Node with escaped quotes"]

Issue 4: Incorrect Cardinality in ER Diagrams

# WRONG
erDiagram
    USER -->-- ORDER

# CORRECT
erDiagram
    USER ||--o{ ORDER : places

Issue 5: Malformed Class Definitions

# WRONG
classDiagram
    class User {
        string name  // wrong comment syntax
    }

# CORRECT
classDiagram
    class User {
        string name
    }

Iterative Validation Workflow

1. Generate the initial diagram
2. Validate using the script
3. If errors found:
   • Parse error message from script output
   • Identify the problematic syntax
   • Fix the issue
   • Validate again
4. Repeat until validation passes (max 3 attempts)
5. Confirm with success message

Error Recovery

If validation fails repeatedly (after 3 attempts):

1. Simplify the diagram to the minimal working example
2. Validate the simple version
3. Add complexity incrementally, validating after each addition
4. This identifies the exact syntax causing the issue

Best Practices

• Always validate before showing to user - never present unvalidated diagrams
• Use the script for all validation - don't use inline npx commands
• Always quote labels containing spaces, colons, or special characters
• Use consistent arrow styles within the same diagram
• Test complex diagrams incrementally - build and validate in stages
• Reference documentation when unsure about syntax
• Provide clear diagram titles for better understanding
• Use comments (%%) to document complex sections

Output Format

When presenting diagrams to users:

## Diagram Title

Brief description of what the diagram represents.

\```mermaid
diagram-code-here
\```

**Validation Status**: ✅ Validated successfully

Examples

Example 1: Creating a Flowchart

User Request: "Create a flowchart for user authentication"

Process:

1. Create the diagram
2. Validate using script
3. Present to user

flowchart TD
    Start([User Login]) --> Input[Enter credentials]
    Input --> Validate{Valid credentials?}
    Validate -->|Yes| CheckMFA{MFA enabled?}
    Validate -->|No| Error[Show error message]
    Error --> Input
    CheckMFA -->|Yes| MFA[Verify MFA code]
    CheckMFA -->|No| Success[Grant access]
    MFA --> MFACheck{MFA valid?}
    MFACheck -->|Yes| Success
    MFACheck -->|No| Error
    Success --> End([Dashboard])

Validation command:

echo 'flowchart TD
    Start([User Login]) --> Input[Enter credentials]
    Input --> Validate{Valid credentials?}
    Validate -->|Yes| CheckMFA{MFA enabled?}
    Validate -->|No| Error[Show error message]
    Error --> Input
    CheckMFA -->|Yes| MFA[Verify MFA code]
    CheckMFA -->|No| Success[Grant access]
    MFA --> MFACheck{MFA valid?}
    MFACheck -->|Yes| Success
    MFACheck -->|No| Error
    Success --> End([Dashboard])' | base/skills/mermaid/scripts/validate_mermaid.sh

Result: ✅ Validated successfully

Example 2: Creating a Sequence Diagram

User Request: "Show API authentication flow"

sequenceDiagram
    participant Client
    participant API
    participant AuthService
    participant Database

    Client->>+API: POST /login {username, password}
    API->>+AuthService: Validate credentials
    AuthService->>+Database: Query user
    Database-->>-AuthService: User data
    AuthService->>AuthService: Verify password hash

    alt Credentials valid
        AuthService-->>API: Generate JWT token
        API-->>Client: 200 OK {token}
    else Invalid credentials
        AuthService-->>API: Authentication failed
        API-->>Client: 401 Unauthorized
    end

    deactivate AuthService
    deactivate API

Validation: ✅ Passes validation

Example 3: Fixing a Validation Error

Initial attempt (invalid):

stateDiagram-v2
    [*] --> Idle
    Idle -> Running : start
    Running -> Idle : stop

Validation:

echo 'stateDiagram-v2
    [*] --> Idle
    Idle -> Running : start
    Running -> Idle : stop' | base/skills/mermaid/scripts/validate_mermaid.sh

Output:

❌ Diagram stdin: Invalid
Error: Parse error on line 3

Analysis: Arrow syntax wrong - should be --> not ->

Fixed version:

stateDiagram-v2
    [*] --> Idle
    Idle --> Running : start
    Running --> Idle : stop

Validation: ✅ Success

Example 4: Complex ER Diagram

User Request: "Database schema for e-commerce"

erDiagram
    CUSTOMER ||--o{ ORDER : places
    CUSTOMER {
        int customer_id PK
        string email
        string name
        date created_at
    }

    ORDER ||--|{ ORDER_ITEM : contains
    ORDER {
        int order_id PK
        int customer_id FK
        date order_date
        decimal total_amount
        string status
    }

    ORDER_ITEM }o--|| PRODUCT : references
    ORDER_ITEM {
        int order_item_id PK
        int order_id FK
        int product_id FK
        int quantity
        decimal price
    }

    PRODUCT {
        int product_id PK
        string name
        string description
        decimal price
        int stock_quantity
    }

    PRODUCT }o--|| CATEGORY : belongs_to
    CATEGORY {
        int category_id PK
        string name
        string description
    }

Validation: ✅ All syntax validated

Script Location

The validation scripts are located at:

• Bash: base/skills/mermaid/scripts/validate_mermaid.sh
• PowerShell: base/skills/mermaid/scripts/validate_mermaid.ps1

Run them with:

• Bash: echo 'diagram' | .../validate_mermaid.sh
• PowerShell: $diagram | .../validate_mermaid.ps1

Resources

• Cheat Sheet: See reference.md for comprehensive syntax examples
• Script Documentation: See scripts/README.md for script usage details
• Official Docs: https://mermaid.js.org/
• Live Editor: https://mermaid.live/

Success Criteria

A diagram is complete when:

1. ✅ Syntax is correct for the diagram type
2. ✅ Validation passes with validate_mermaid.sh or validate_mermaid.ps1 script
3. ✅ Diagram accurately represents the requested information
4. ✅ Labels are clear and properly quoted
5. ✅ Styling is appropriate (if requested)
6. ✅ Comments document complex sections (if needed)