betto_schema

Pure Dart JSON Schema 2020-12 library. Typed, composable validators, a full keyword rule tree, and format validators for email, URI, date-time, UUID, and more.

0.1.0-dev.2 bettongia/schema

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Last release 1 months ago

07 Jul 2026

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2 months old

2 releases · first in 2026

2 releases in the last 12 months

see the full history below

Release timeline

2 releases · Jun 2026 to Jul 2026

Release Pre-release

Releases

latest 2

0.1.0-dev.2 07 Jul 2026 pre-release

Release notes

betto_common
Open source →
Release notes
- Removed the redundant Range class as it was a replica of the one in betto_common.
Open source →

0.1.0-dev.1 16 Jun 2026 pre-release

Release notes

Documentation and build refinement ready for release

Open source →

Release notes

Initial development release. Pure Dart JSON Schema validation primitives aligned with JSON Schema Validation 2020-12.

Primitive validators (`validation.dart`)

Typed, composable validators that form the primary public API. Dart developers construct and combine these directly without touching JSON Schema format.

Validator	Description
`EnumValidator<T>`	Value must be one of a declared set
`ConstValidator<T>`	Value must equal a constant (deep equality)
`Minimum<T>` / `Maximum<T>`	Inclusive numeric bounds
`ExclusiveMinimum<T>` / `ExclusiveMaximum<T>`	Exclusive numeric bounds
`MultipleOf<T>`	Divisibility check (floating-point-safe)
`InRange`	Value within a `Range`
`MinimumLength` / `MaximumLength` / `ExactLength`	Unicode-aware string length
`InRangeLength`	String length within a `Range`
`PatternValidator`	Regex match (unanchored, per JSON Schema §6.3.3)
`MinItems<T>` / `MaxItems<T>` / `ItemCount<T>`	Array size bounds
`UniqueItems<T>`	All array elements pairwise distinct (deep equality)
`ItemsValidator<T>`	Every array element satisfies a sub-validator
`MinProperties` / `MaxProperties`	Object property count bounds
`Required`	All named properties present in a map
`TypeValidator`	JSON Schema type check — single string and array form
`PropertiesValidator`	Per-key validators for a map
`AdditionalPropertiesValidator`	Rejects undeclared object keys
`DependentRequired`	Conditional required properties

JSON Schema rule tree (`schema_rule.dart`)

A sealed SchemaRule hierarchy compiled from a JSON Schema by SchemaParser. All rules collect every violation in a single pass so callers receive the complete error list at once.

Rule	JSON Schema keyword(s)
`TypeRule`	`type` (string and array forms)
`RequiredRule`	`required`
`PropertiesRule`	`properties`
`AdditionalPropertiesRule`	`additionalProperties: false`
`AdditionalPropertiesSchemaRule`	`additionalProperties: <schema>`
`EnumRule`	`enum`
`ConstRule`	`const`
`NumericRule`	`minimum`, `maximum`, `exclusiveMinimum`, `exclusiveMaximum`
`MultipleOfRule`	`multipleOf`
`StringRule`	`minLength`, `maxLength`, `pattern`
`FormatRule`	`format`
`ArrayRule`	`minItems`, `maxItems`, `items`
`PrefixItemsRule`	`prefixItems`
`ContainsRule`	`contains`, `minContains`, `maxContains`
`UniqueItemsRule`	`uniqueItems`
`ObjectSizeRule`	`minProperties`, `maxProperties`
`PatternPropertiesRule`	`patternProperties`
`DependentRequiredRule`	`dependentRequired`
`CompositeRule`	(internal — runs multiple rules in one pass)
`AlwaysInvalidRule`	`false` boolean schema (e.g. `items: false`)

Format validators (`formats/`)

StringFormatValidator provides named format validators. The set covers all standard JSON Schema 2020-12 format strings implemented in this release, plus project-specific extensions.

Standard JSON Schema formats

Format	Spec
`uri`	RFC 3986
`urn`	RFC 8141
`email`	RFC 5322 (pragmatic subset)
`date-time`	ISO 8601
`date`	RFC 3339
`time`	RFC 3339
`uuid`	RFC 9562
`duration`	ISO 8601 / RFC 3339
`hostname`	RFC 1123
`idn-hostname`	RFC 5890 (best-effort; Punycode conformance not enforced)
`ipv4`	RFC 2673 — four decimal octets 0–255, leading zeros rejected
`ipv6`	RFC 4291 — full and `::` compressed forms, IPv4-mapped accepted
`uri-reference`	RFC 3986 §4.1 — absolute URI or relative reference
`json-pointer`	RFC 6901
`relative-json-pointer`	IETF draft
`regex`	ECMA-262 dialect

Deferred to v1: idn-email, iri, iri-reference, uri-template.

Project-specific extensions

Format	Description
`hex-string`	Hexadecimal digit string
`digit-string`	Decimal digit string
`roman-numeral`	Roman numeral string
`isbn-13`	ISBN-13 with check-digit verification
`doi`	Digital Object Identifier
`lang`	BCP 47 / RFC 5646 language tag

Porcelain (`json_schema_validator.dart`)

JsonSchemaValidator accepts a JSON Schema as a String or Map<String, dynamic>, delegates to SchemaParser, and returns List<SchemaViolation>. No validation logic of its own.

Supporting types

SchemaViolation — dot-path (path) and human-readable message; root violations use an empty path
SchemaParser — compiles Map<String, dynamic> JSON Schema to a SchemaRule tree; unknown keywords are silently ignored
Range — inclusive/exclusive numeric range helper used by primitive validators

Spec-correctness fixes applied during this release

pattern is unanchored — hasMatch() not a full-string check (JSON Schema §6.3.3)
integer accepts whole-number doubles (e.g. 1.0); non-finite values rejected (§6.1.1)
type array form (["string", "null"]) is parsed and validated correctly (§6.1.1)
uri and urn format validators correctly distinguished (were swapped)

Examples (`example/`)

Six runnable examples are included:

Entry point	Demonstrates
`example/main.dart`	Parsing a JSON Schema with `SchemaParser` and collecting `SchemaViolation`s
`example/validators.dart`	Composing `Validator` primitives directly (`MaximumLength`, `StringFormatValidator`)
`example/violation.dart`	Constructing and printing `SchemaViolation` values
`example/book/main.dart`	A book schema: enum genres, `prefixItems`, `additionalProperties`, `contains`, format strings
`example/contact/main.dart`	A contact schema: nested address object, `email`/`uri`/`date` formats, `uniqueItems`, patterns
`example/recipe/main.dart`	A recipe schema: nested ingredient objects, numeric ranges, enum values, `uniqueItems`

Each domain example (book, contact, recipe) ships with a schema.json and sample data files so it can be run standalone with dart run.

CLI

Added bin/validate.dart — a command-line tool that validates a JSON data file (or stdin) against a JSON Schema file. Exits 0 on success, 1 on validation failures (violations printed to stdout), and 2 on usage or I/O errors.

Out of scope (planned for v1)

$ref, allOf / anyOf / oneOf / not, if / then / else, nested $schema declarations, idn-email, iri, iri-reference, uri-template.