Er diagram

Skill shuakami/paperchart/skills/er-diagram

Quiet, editorial chart PNGs for technical blog posts. 15 primitives, six themes, one CLI.

Install

npx -y skills add shuakami/paperchart --skill er-diagram

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What its author says it does

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Render an entity-relationship diagram (Mermaid `erDiagram` equivalent). Each entity is a table-style box with a header (name + caption) and a list of typed fields with PK / FK markers. Relationships are drawn as bézier curves with crow's-foot cardinality markers at each end ("1", "0..1", "M", "1..M", "0..M"). Good for database schema diagrams in technical posts.

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SKILL.md

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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

code	meaning	marker
`"1"`	exactly one	single tick
`"0..1"`	zero or one	circle + tick
`"M"`	many	crow's foot
`"1..M"`	one or many	tick + crow's foot
`"0..M"`	zero or many	circle + crow's foot

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