ALTCHA Flutter Widget

The AltchaWidget is a CAPTCHA-like Flutter component that provides a secure, privacy-friendly way to verify that a user is human—without annoying them. It uses a cryptographic proof-of-work mechanism combined with an optional code challenge, making it resilient against bots and spam.

ALTCHA is an open-source alternative to traditional CAPTCHA, designed to be fast, accessible, and privacy-respecting.

For more information and documentation, visit altcha.org.

Features

• Native Flutter widget – no WebView required
• Privacy-friendly, CAPTCHA-like verification
• Supports image and audio code challenge with ALTCHA Sentinel (adaptive CAPTCHA)
• Localizations support

Screenshots

Installation

Add the following to your pubspec.yaml:

dependencies:
  altcha_widget:
    git:
      url: https://github.com/altcha-org/altcha-flutter.git

Or, if published on pub.dev:

dependencies:
  altcha_widget: ^1.0.0

Then run:

flutter pub get

Usage

import 'package:altcha_widget/widget.dart';

AltchaWidget(
  challengeUrl: 'https://api.example.com/altcha/challenge',
  debug: true,
  onVerified: (payload) {
    // Send the payload to your backend
    print('Payload: $payload');
  },
)

Parameters

One of the challengeUrl or challengeJson is required. Receive the ALTCHA payload, that you send to the server, via onVerified.

Name	Type	Description
challengeUrl	String?	URL to fetch the challenge JSON
challengeJson	Map<String, dynamic>?	Challenge object provided directly
verifyUrl	String?	Server endpoint to verify the solution
onFailed	ValueChanged<Object>?	Called with an exception object on verification failure
onVerified	ValueChanged<String>?	Called with encoded payload after verification
onServerVerification	ValueChanged<AltchaServerVerification>?	Called with server verification result
delay	int?	Optional delay before solving (ms)
debug	bool	Enable verbose logging
hideLogo	bool?	Hide the ALTCHA logo
hideFooter	bool?	Hide the footer text
httpClient	http.Client?	Custom HTTP client (optional)
httpHeaders	Map<String, String>?	Custom HTTP headers (optional)

Localization

To support different languages, include AltchaLocalizationsDelegate:

import 'package:altcha_widget/localizations.dart';

return MaterialApp(
  localizationsDelegates: [
    AltchaLocalizationsDelegate(),
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
  supportedLocales: const [
    Locale('en'),
    Locale('de'),
    Locale('es'),
    Locale('fr'),
    Locale('it'),
    Locale('pt'),
  ],
  ...
);

You can also override or add your own translations using AltchaLocalizationsDelegate(customTranslations):

return MaterialApp(
  localizationsDelegates: [
    AltchaLocalizationsDelegate(
      customTranslations: {
        'en': {
          // Define translations keys here
          'label': 'I am human',
        },
      },
    ),
    GlobalMaterialLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
  ],
  ...
);

Example App

cd example/
flutter run

License

MIT License