ERD

The ERD format is a small, focused language for entity relationship diagrams: entities, attributes with key markers, and relationships written with cardinality symbols.

It is a good fit when you want classic ER output and find Mermaid's ER syntax limiting.

#What it is good at

Classic ER diagrams with explicit key and attribute markers.
Academic or specification contexts where the notation is expected.
Schemas where you want attributes listed but not full column types.

#What it draws

Diagram	Syntax starts with
Entity	[Person]
Primary key	*name
Foreign key	+department_id
Attribute	height
Relationship	Person *--1 Department

#A worked example

Entities, keys and cardinality:

The source, which you can paste into a new diagram and edit:

[Person]
*id
name
height
+department_id

[Department]
*id
name
budget

[Project]
*id
name
+lead_id

Person *--1 Department
Project *--1 Person

#A few things that catch people out

The cardinality symbols are ?, 1, * and +, and they go on both sides of the relationship.
Attributes are listed under the entity, one per line, with * marking keys.
For types, defaults and indexes, DBML is the better tool.

Structurizr

One model, many views.

Nomnoml

Lightweight UML with almost no syntax.

Examples

Working diagrams you can copy.

Learn one properly. Borrow the rest when you need them.

ERD