Luthor

Luthor is a validation library for Dart and Flutter, heavily inspired by zod.

• Build validators with a fluent API: l.string().email().required().
• Get typed output without code generation: l.int().required() validates to an int.
• Read structured issues, each with a code, a path, a message and params.
• Translate or rewrite every message with one message builder.

Installation

Dart:

dart pub add luthor

Flutter:

flutter pub add luthor

Usage

import 'package:luthor/luthor.dart';

final signup = l.schema({
  'email': l.string().email().required(),
  'password': l.string().min(8).required(),
  'tags': l.list(l.string().required()),
});

void main() {
  final result = signup.validate({
    'email': 'not-an-email',
    'password': 'short',
    'tags': ['dart', 1],
  });

  switch (result) {
    case ValidationSuccess(:final data):
      print('Valid: $data');
    case ValidationFailure(:final errors):
      // {email: [email must be a valid email address],
      //  password: [password must be at least 8 characters long],
      //  tags.1: [tags must be a string]}
      print(errors);
  }

  print(result.getError('tags.1')); // tags must be a string
}

Validators are optional by default: null, and a missing schema field, pass unless .required() is present.

Code Generation (Optional)

Luthor supports code generation for enhanced type safety and developer experience:

dart pub add dev:build_runner dev:luthor_generator

Features include:

• Type-safe ErrorKeys - Generated constants for accessing validation errors
• Type-safe SchemaKeys - Generated constants for defining schemas
• Cross-field validation - Validate fields against other fields in the same schema

See the documentation for usage.