Markdown ER diagram maker

Design a database schema as an entity-relationship diagram. Describe your tables and relationships in Mermaid and get a clean ER diagram to drop straight into your docs.

Mermaid ER syntax

An ER diagram is a set of entities (tables) and the relationships between them. You name each entity, list its fields, then draw a line for each relationship with its cardinality. Here is each piece you can write.

Entities and fields

Name an entity and list its fields inside braces, each as a type then a name. Add PK or FK to mark keys.

You write

erDiagram
  CUSTOMER {
    int id PK
    string name
  }

You get

Relationships and cardinality

Connect two entities. The marks on each end set how many rows relate: one, zero-or-one, or many.

You write

erDiagram
  CUSTOMER ||--o{ ORDER : places
  ORDER ||--|{ LINE : contains

You get

Cheat sheet

Write this	You get
Fields
`int id PK`	Primary key field
`int owner_id FK`	Foreign key field
`string name`	Plain field
Cardinality (one end)
`\|\|`	Exactly one
`\|o`	Zero or one
`}o / o{`	Zero or many
`}\| / \|{`	One or many
Relationship
`A \|\|--o{ B : label`	Solid (identifying) relationship
`A \|\|..o{ B : label`	Dashed (non-identifying)