Paperchart Er Diagram

paperchart — ER diagram

Table-style entity boxes with typed fields and PK / FK markers, connected by relationship lines with crow's-foot cardinality.

When to use

• Database schema walkthroughs.
• Explaining multi-table joins in a blog post.
• Any entity-with-attributes diagram.

Input shape

{
  "data": {
    "entities": [
      { "id": "user", "label": "user", "caption": "account", "fields": [
        { "name": "id",         "type": "uuid",      "pk": true },
        { "name": "email",      "type": "text",                "note": "unique" },
        { "name": "created_at", "type": "timestamp" }
      ] },
      { "id": "org",  "label": "organization", "fields": [
        { "name": "id",   "type": "uuid", "pk": true },
        { "name": "name", "type": "text" }
      ] },
      { "id": "membership", "label": "membership", "accent": true, "fields": [
        { "name": "user_id", "type": "uuid", "pk": true, "fk": true },
        { "name": "org_id",  "type": "uuid", "pk": true, "fk": true },
        { "name": "role",    "type": "enum" }
      ] }
    ],
    "relationships": [
      { "from": "user", "to": "membership", "fromCard": "1", "toCard": "0..M", "label": "joins" },
      { "from": "org",  "to": "membership", "fromCard": "1", "toCard": "0..M", "label": "contains" }
    ]
  }
}

Cardinality codes

Field options

• pk: true — adds a bold PK marker and uses medium weight for the name.
• fk: true — adds FK marker.
• type — right-aligned type label (uuid, text, enum, timestamp, ...).
• note — reserved for future rendering (currently stored, not drawn).

Layout

Entities are arranged in a fixed grid (default 3 columns). Override with layout.columns if you need a different split.

CLI

paperchart er-diagram -i data.json -o er.png
paperchart er-diagram --defaults -o er.png