mermaid-erd

name	mermaid-erd
description	Generate a Mermaid ERD from SQL schema files
allowed-tools	Read, Glob, Grep, Bash(npx:*)

Analyze SQL schema files and generate a Mermaid entity relationship diagram.

Arguments: Path to SQL file(s) or directory containing schema files (*.sql)

Steps:

1. Find and read all relevant SQL schema files

2. Parse each table definition extracting:

   • Table name
   • Columns with types
   • Primary keys (PK)
   • Foreign keys (FK) and their references
   • Unique constraints (UK)

3. Generate a Mermaid erDiagram showing:

   • Each table as an entity with its columns
   • Relationships based on foreign keys
   • Cardinality notation (one-to-one, one-to-many, many-to-many)

4. Validate diagram by running: npx -y @mermaid-js/mermaid-cli mmdc -i /dev/stdin -o /dev/null <<< '<diagram>'

   • If validation fails, fix syntax errors and retry

5. Verify complete coverage:

   • List any tables not included in the diagram
   • List any foreign key relationships not represented

Output format:

erDiagram
    users {
        int id PK
        string email UK
        string name
        timestamp created_at
    }

    posts {
        int id PK
        int user_id FK
        string title
        text content
    }

    users ||--o{ posts : "has many"

Relationship notation:

• ||--|| one-to-one
• ||--o{ one-to-many
• o{--o{ many-to-many (via junction table)

Notes:

• Simplify SQL types to readable names (VARCHAR -> string, INTEGER -> int, etc.)
• Include PK/FK/UK markers on relevant columns
• Name relationships descriptively when possible
• For large schemas, consider grouping related tables or generating multiple diagrams