gskinnerteam/flutter-hatcha-app/json-schema-builder

Name: json-schema-builder
Author: gskinnerteam

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gskinnerteam/flutter-hatcha-app
.github/skills/json-schema-builder/SKILL.md
Updated 1 Oct 2026
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Dart DSL for building and validating JSON Schemas (Draft 2020-12). Use when: defining schemas with S.object, S.string, S.list, S.integer, S.number, S.boolean, S.nil, S.combined, S.any, Schema, ObjectSchema, StringSchema, ListSchema, NumberSchema, IntegerSchema, BooleanSchema, NullSchema, working with schema validation, ValidationError, SchemaRegistry, or schema composition (allOf, anyOf, oneOf, not, if/then/else).

Install

npx vskill@latest install gskinnerteam/flutter-hatcha-app/json-schema-builder

SKILL.md

json_schema_builder Package — API Reference

The json_schema_builder package (v0.1.3) provides a fluent, type-safe Dart DSL for building, composing, and validating JSON Schemas compliant with Draft 2020-12. It is the schema backbone for GenUI catalogue item definitions.

When to Use

Defining dataSchema for a CatalogItem
Building JSON schemas programmatically (any context)
Working with S.object, S.string, S.list, or other schema factories
Composing schemas with allOf, anyOf, oneOf, not, if/then/else
Validating data against a schema
Using $ref / $defs for schema reuse

DSL Quick Reference

The Schema extension type wraps Map<String, Object?> and provides factory constructors for all schema types.

dart

typedef S = Schema;  // Shortcut — use S.object(), S.string(), etc.

Factory Constructors

Constructor	Returns	Purpose
`S.string()`	`StringSchema`	String with optional constraints
`S.integer()`	`IntegerSchema`	Integer with optional range
`S.number()`	`NumberSchema`	Number (int or double) with optional range
`S.boolean()`	`BooleanSchema`	Boolean value
`S.list()`	`ListSchema`	Array with item schemas
`S.object()`	`ObjectSchema`	Object with typed properties
`S.nil()`	`NullSchema`	Null value
`S.any()`	`Schema`	No type constraint
`S.combined()`	`Schema`	Composition (allOf/anyOf/oneOf/not/if-then-else)
`S.fromMap(map)`	`Schema`	Wrap raw map
`S.fromBoolean(bool)`	`Schema`	`true` = accept all, `false` = reject all

Schema Types

StringSchema

dart

S.string({
  String? title,
  String? description,
  List<Object?>? enumValues,     // Fixed choices
  Object? constValue,            // Exact match
  int? minLength,
  int? maxLength,
  String? pattern,               // Regex pattern
  String? format,                // 'email', 'date-time', 'date', 'time', 'ipv4', 'ipv6'
})

Examples:

dart

S.string(description: 'User email.', format: 'email')
S.string(minLength: 3, maxLength: 20, pattern: r'^[a-z0-9]+$')
S.string(enumValues: ['horizontal', 'vertical'])

ObjectSchema

dart

S.object({
  String? title,
  String? description,
  Map<String, Schema>? properties,
  Map<String, Schema>? patternProperties,   // Regex-keyed property validation
  List<String>? required,
  Map<String, List<String>>? dependentRequired,
  Object? additionalProperties,             // Schema or bool
  Object? unevaluatedProperties,            // Schema or bool
  Schema? propertyNames,
  int? minProperties,
  int? maxProperties,
})

Example:

dart

S.object(
  description: 'User profile.',
  required: ['id', 'email'],
  properties: {
    'id': S.string(minLength: 1),
    'email': S.string(format: 'email'),
    'age': S.integer(minimum: 18),
    'active': S.boolean(),
  },
  additionalProperties: false,
)

ListSchema (Array)

dart

S.list({
  String? title,
  String? description,
  Schema? items,                 // Schema for all items (after prefixItems)
  List<Schema>? prefixItems,     // Positional schemas (tuple validation)
  Object? unevaluatedItems,      // Schema or bool
  Schema? contains,              // At least one item must match
  int? minContains,
  int? maxContains,
  int? minItems,
  int? maxItems,
  bool? uniqueItems,
})

Example:

dart

S.list(
  description: 'Tags list, 1-10 unique strings.',
  items: S.string(),
  uniqueItems: true,
  minItems: 1,
  maxItems: 10,
)

NumberSchema

dart

S.number({
  String? title,
  String? description,
  num? minimum,              // Inclusive
  num? maximum,              // Inclusive
  num? exclusiveMinimum,     // Exclusive
  num? exclusiveMaximum,     // Exclusive
  num? multipleOf,
})

IntegerSchema

dart

S.integer({
  String? title,
  String? description,
  int? minimum,
  int? maximum,
  int? exclusiveMinimum,
  int? exclusiveMaximum,
  num? multipleOf,
})

BooleanSchema

dart

S.boolean({String? title, String? description})

NullSchema

dart

S.nil({String? title, String? description})

Core Schema Methods

Method	Signature	Purpose
`validate`	`Future<List<ValidationError>> validate(Object? data, {...})`	Validate data against schema
`toJson`	`String toJson({String? indent})`	Convert to JSON string
`value`	`Map<String, Object?>`	Raw underlying map
`[]`	`Object? operator [](String key)`	Access keyword by name

Metadata Getters

All standard JSON Schema metadata keywords are accessible as properties:

dart

schema.title         // String?
schema.description   // String?
schema.$comment      // String?
schema.defaultValue  // Object?
schema.examples      // List<Object?>?
schema.deprecated    // bool?
schema.readOnly      // bool?
schema.writeOnly     // bool?

GenUI Integration

Schemas define the AI contract for CatalogItem.dataSchema. The description field in each property acts as a system prompt for the AI — be explicit about constraints.

dart

final _schema = S.object(
  description: 'A slider for selecting a numeric value.',
  required: ['label', 'value'],
  properties: {
    'label': S.string(description: 'Display label above the slider.'),
    'value': A2uiSchemas.numberReference(
      description: 'State reference for the slider value. Range 0-100.',
    ),
    'min': S.number(description: 'Minimum value. Default 0.'),
    'max': S.number(description: 'Maximum value. Default 100.'),
  },
);

Static display properties use raw S.* types. Editable / data-bound properties use A2uiSchemas.* references. See the genui skill's data-binding reference for the full decision table.

Advanced Topics

For schema composition (allOf/anyOf/oneOf/not/if-then-else), $ref/$defs, validation API, and advanced features, see advanced.md.

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Source

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Popularity

Repository stars: 66
Repository forks: 7
7-day trend score: 21

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