Ack

pub package CI/CD Documentation

Ack is a schema validation library for Dart and Flutter that helps you validate data with a simple, fluent API. Ack is short for "acknowledge".

Why Use Ack?

  • Simplify Validation: Easily handle complex data validation logic
  • Validate external payloads: Guard API and user inputs by validating required fields, types, and constraints at boundaries
  • Single Source of Truth: Define data structures and rules in one place
  • Reduce Boilerplate: Minimize repetitive code for validation and JSON conversion
  • Type Safety: Generate immutable models from schemas, or derive validated schemas from hand-written classes

Quick Start

dart pub add ack

import 'package:ack/ack.dart';

// Define a schema for a user object
final userSchema = Ack.object({
  'name': Ack.string().minLength(2).maxLength(50),
  'email': Ack.string().email(),
  'age': Ack.integer().min(0).max(120).optional(),
});

// Validate data against the schema
final result = userSchema.safeParse({
  'name': 'John Doe',
  'email': 'john@example.com',
  'age': 30,
});

if (result.isOk) {
  final validData = result.getOrThrow();
  print('Valid user: $validData');
} else {
  final error = result.getError();
  print('Validation failed: $error');
}

Use .optional() when a field may be omitted entirely. Chain .nullable() if a present field may hold null, or combine both for an optional-and-nullable value.

Import JSON Schema

Import a decoded draft 2020-12 schema without re-declaring it in Dart:

import 'package:ack/ack.dart';

final AckSchema<Object, Object> schema = Ack.fromJsonSchema({
  'type': 'object',
  'properties': {'name': {'type': 'string'}},
  'required': ['name'],
});
final value = schema.parse({'name': 'Ada'});
final jsonSchema = schema.toJsonSchema();

The source document is a decoded map or boolean, not a JSON string. Ack.fromJsonSchema() returns an executable validator and rejects unsupported semantics with JsonSchemaImportException; its immutable diagnostics identify the source keyword and location. Supply reference bundles with documents and baseUri; no references are fetched automatically.

Exports preserve supported validation behavior, not textual document identity. Full A2UI coverage is not supported. MCP registration compatibility remains separate. See the JSON Schema guide for the supported subset, recursive bundles, and round-trip guarantees.

Documentation

Libraries

ack
ACK - A validation library for Dart