Checkit

Checkit is a modular, extensible validation library for Dart. It supports validation chains, localization, custom rules, and flexible configuration. Perfect for both client and server use cases.

✨ Features

• Simple and readable builder-style API
• Custom validators
• Localization support with easy customization
• String, num, int, double, string-date, datetime, IP, password and subnet validators
• Easy to extend and integrate
• Zero dependencies (pure Dart)

🚀 Quick Start

Installation

Add the following dependency to your project:

dependencies:
  checkit: ^1.0.0

Or run via CLI for Dart:

dart pub add checkit

Or for Flutter:

flutter pub add checkit

Basic Usage

import 'package:checkit/checkit.dart';

final result = Checkit.string
  .min(5)
  .max(10)
  .email()
  .validateOnce("example@mail.com");

if (result.isValid) {
  print("Success!");
} else {
  print("Error: ${result.errors}");
}

Or even simpler with prettyPrint() method:

import 'package:checkit/checkit.dart';

final result = Checkit.string
  .min(5)
  .max(10)
  .email()
  .validateOnce("example@mail.com");

result.prettyPrint();

🔧 Built-in Validators

String Validator

Checkit.string
  .min(3)
  .max(20)
  .startsWith("abc")
  .validateOnce("abc123");

Available String Validations:

• min, max, exact, range
• email
• alpha, alphanumeric
• contains, hasSymbols, hasRepeats
• isDouble, isInt
• jwt, pattern
• equals, endsWith, startsWith

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

And refs to other nodes:

• dateTime, dateTimeAuto, dateTimeIso
• password
• ip, subnet

Number Validator

Checkit.num
  .positive()
  .range(10, 100)
  .validateOnce(42);

Available Num Validations:

• min, max, range
• positive, negative
• multiple

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

Integer Validator

Checkit.int
  .positive()
  .range(10, 100)
  .validateOnce(42);

Available Num Validations:

• min, max, range, rangeWithStep
• positive, negative
• multiple
• digitCount
• divisibleBy
• even, odd, prime
• oneOf

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

Double Validator

Checkit.double
  .positive()
  .range(10, 100)
  .validateOnce(42);

Available Double Validations:

• min, max, range
• positive, negative
• decimal, finite, integer

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

Password Validator

Checkit.string
  .password()
  .min(8)
  .hasUppercase()
  .hasDigit()
  .noSpace()
  .validateOnce("S3cureP@ss");

Available Password Validations:

• typical, simple, strong
• min, max, exact
• hasUppercase, hasLowercase, hasDigit, hasLetter, hasSpecial, hasSymbols
• noSpace, noRepeats

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

Date Validator (from String)

If the format is known

Checkit.string
  .dateTime("yyyy-MM-dd")
  .notFuture()
  .validateOnce("2023-12-01");

If the format is unknown

Be careful, as it can determine the month and day values ​​itself through the method for cases when the date does not give an unambiguous correspondence.

Checkit.string
  .dateTimeAuto()
  .notFuture()
  .validateOnce("2023/12/01");

Available Date (String) Validations:

• format
• maxYear, minYear
• notPast, notFuture
• before, after, range
• leapYear
• iso8601

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

DateTime Validator

Checkit.dateTime.notFuture().validateOnce(DateTime(2023, 12, 1));

Available DateTime Validations:

• maxYear, minYear
• notPast, notFuture
• before, after, range
• leapYear

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

IP & Subnets

Checkit.string.ip().v4().validateOnce("192.168.0.1");

Available IP Validations:

• v4, v6
• inSubnet
• linkLocal, localhost, loopback
• range

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

Checkit.string.subnet("192.168.0.0/24").contains("192.168.0.42");

Available Subnet Validations:

• contains

Special methods:

• custom, not, clone, withContext, build, validateOnce, any, every

🔁 Inverting Validators with .not()

Checkit supports expressive validation chains — including the ability to invert any validator using the .not(...) method. This allows you to declare what a value must not contain in a readable, declarative way.

Use Case: Excluding Specific Characters in a Password

For example, imagine you want to validate that a password must contain certain characters (e.g., "B", "C", "D"), but must not contain "A" or "F". With Checkit, this becomes simple and expressive:

void main() {
  final validator = Checkit.string
      .password()
      .not(StringValidator.hasSymbols('A'), error: 'Value must not be A')
      .hasSymbols('BCD')
      .not(StringValidator.hasSymbols('F'), error: 'Value must not be F');

  final password = 'ABCDEF';
  final result = validator.validateOnce(password);

  result.prettyPrint();
}

Output

❌ Invalid
  1. Value must not be A
  2. Value must not be F

Any standard validator can be inverted via:

.not(validator, error: 'Custom error message')

⚙️ Configuration

You can globally configure Checkit:

Checkit.config = ValidatorConfig(
  stopOnFirstError: true,
  usePermanentCache: true,
);

Or use your own ValidationContext:

final context = Checkit.config.copyWith(stopOnFirstError: false).buildContext();
Checkit.string.withContext(context).min(5).validateOnce("test");

🌍 Localization

Checkit uses English error messages by default. You can provide your own:

Checkit.config = ValidatorConfig(
  errors: MyCustomErrors(), // Implements ICheckitErrors
);

You can also integrate intl using an optional checkit_intl package (planned).

🧩 Custom Validators

Create your own validator:

class CustomValidator {
  static Validator<String> onlyLowercase({String? error}) {
    return (value, context) {
      if (value != null && value == value.toLowerCase()) return null;
      return error ?? context.errors.generalErrors.invalidValue;
    };
  }
}

// Usage:
Checkit.string.custom(CustomValidator.onlyLowercase(), error: "Lowercase only");

🧪 Testing

final result = Checkit.string.min(5).validateOnce("hi");

expect(result.isValid, false);
expect(result.errors.first.message, contains("Minimum 5 characters"));

📁 Library Structure

• Checkit — Main entry point
• ValidatorConfig — Global configuration
• ValidationContext — Execution context
• ICheckitErrors — Localization interface
• ValidatorSet — Set of validators
• ValidatorNode<T> — Builder-style chain

📌 TODO / Roadmap

• ✅ Custom rules support
• ✅ Localization support
• ⏳ intl integration
• ⏳ Flutter adapter (AppLocalizations integration)

❤️ Author

Crafted with care and a focus on performance. Contributions, issues, and stars are always welcome!