diff --git a/flutter/sherpa_onnx/lib/src/audio_tagging.dart b/flutter/sherpa_onnx/lib/src/audio_tagging.dart
index 3e3dbed2..2e3e30ed 100644
--- a/flutter/sherpa_onnx/lib/src/audio_tagging.dart
+++ b/flutter/sherpa_onnx/lib/src/audio_tagging.dart
@@ -8,11 +8,24 @@ import './sherpa_onnx_bindings.dart';
 class OfflineZipformerAudioTaggingModelConfig {
   const OfflineZipformerAudioTaggingModelConfig({this.model = ''});
 
+  factory OfflineZipformerAudioTaggingModelConfig.fromJson(
+      Map<String, dynamic> map) {
+    return OfflineZipformerAudioTaggingModelConfig(
+      model: map['model'] ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineZipformerAudioTaggingModelConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() {
+    return {
+      'model': model,
+    };
+  }
+
   final String model;
 }
 
@@ -24,11 +37,32 @@ class AudioTaggingModelConfig {
       this.provider = 'cpu',
       this.debug = true});
 
+  factory AudioTaggingModelConfig.fromJson(Map<String, dynamic> map) {
+    return AudioTaggingModelConfig(
+      zipformer:
+          OfflineZipformerAudioTaggingModelConfig.fromJson(map['zipformer']),
+      ced: map['ced'] ?? '',
+      numThreads: map['numThreads'] ?? 1,
+      provider: map['provider'] ?? 'cpu',
+      debug: map['debug'] ?? true,
+    );
+  }
+
   @override
   String toString() {
     return 'AudioTaggingModelConfig(zipformer: $zipformer, ced: $ced, numThreads: $numThreads, provider: $provider, debug: $debug)';
   }
 
+  Map<String, dynamic> toJson() {
+    return {
+      'zipformer': zipformer.toJson(),
+      'ced': ced,
+      'numThreads': numThreads,
+      'provider': provider,
+      'debug': debug,
+    };
+  }
+
   final OfflineZipformerAudioTaggingModelConfig zipformer;
   final String ced;
   final int numThreads;
@@ -39,11 +73,25 @@ class AudioTaggingModelConfig {
 class AudioTaggingConfig {
   AudioTaggingConfig({required this.model, this.labels = ''});
 
+  factory AudioTaggingConfig.fromJson(Map<String, dynamic> map) {
+    return AudioTaggingConfig(
+      model: AudioTaggingModelConfig.fromJson(map['model']),
+      labels: map['labels'] ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'AudioTaggingConfig(model: $model, labels: $labels)';
   }
 
+  Map<String, dynamic> toJson() {
+    return {
+      'model': model.toJson(),
+      'labels': labels,
+    };
+  }
+
   final AudioTaggingModelConfig model;
   final String labels;
 }
@@ -51,11 +99,27 @@ class AudioTaggingConfig {
 class AudioEvent {
   AudioEvent({required this.name, required this.index, required this.prob});
 
+  factory AudioEvent.fromJson(Map<String, dynamic> map) {
+    return AudioEvent(
+      name: map['name'],
+      index: map['index'],
+      prob: map['prob'],
+    );
+  }
+
   @override
   String toString() {
     return 'AudioEvent(name: $name, index: $index, prob: $prob)';
   }
 
+  Map<String, dynamic> toJson() {
+    return {
+      'name': name,
+      'index': index,
+      'prob': prob,
+    };
+  }
+
   final String name;
   final int index;
   final double prob;
diff --git a/flutter/sherpa_onnx/lib/src/feature_config.dart b/flutter/sherpa_onnx/lib/src/feature_config.dart
index 2af7f2cc..01474698 100644
--- a/flutter/sherpa_onnx/lib/src/feature_config.dart
+++ b/flutter/sherpa_onnx/lib/src/feature_config.dart
@@ -3,11 +3,23 @@
 class FeatureConfig {
   const FeatureConfig({this.sampleRate = 16000, this.featureDim = 80});
 
+  factory FeatureConfig.fromJson(Map<String, dynamic> json) {
+    return FeatureConfig(
+      sampleRate: json['sampleRate'] as int? ?? 16000,
+      featureDim: json['featureDim'] as int? ?? 80,
+    );
+  }
+
   @override
   String toString() {
     return 'FeatureConfig(sampleRate: $sampleRate, featureDim: $featureDim)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'sampleRate': sampleRate,
+        'featureDim': featureDim,
+      };
+
   final int sampleRate;
   final int featureDim;
 }
diff --git a/flutter/sherpa_onnx/lib/src/keyword_spotter.dart b/flutter/sherpa_onnx/lib/src/keyword_spotter.dart
index 310657d1..4580b8e3 100644
--- a/flutter/sherpa_onnx/lib/src/keyword_spotter.dart
+++ b/flutter/sherpa_onnx/lib/src/keyword_spotter.dart
@@ -23,11 +23,40 @@ class KeywordSpotterConfig {
     this.keywordsBufSize = 0,
   });
 
+  factory KeywordSpotterConfig.fromJson(Map<String, dynamic> json) {
+    return KeywordSpotterConfig(
+      feat: json['feat'] != null
+          ? FeatureConfig.fromJson(json['feat'] as Map<String, dynamic>)
+          : const FeatureConfig(),
+      model: OnlineModelConfig.fromJson(json['model'] as Map<String, dynamic>),
+      maxActivePaths: json['maxActivePaths'] as int? ?? 4,
+      numTrailingBlanks: json['numTrailingBlanks'] as int? ?? 1,
+      keywordsScore: (json['keywordsScore'] as num?)?.toDouble() ?? 1.0,
+      keywordsThreshold:
+          (json['keywordsThreshold'] as num?)?.toDouble() ?? 0.25,
+      keywordsFile: json['keywordsFile'] as String? ?? '',
+      keywordsBuf: json['keywordsBuf'] as String? ?? '',
+      keywordsBufSize: json['keywordsBufSize'] as int? ?? 0,
+    );
+  }
+
   @override
   String toString() {
     return 'KeywordSpotterConfig(feat: $feat, model: $model, maxActivePaths: $maxActivePaths, numTrailingBlanks: $numTrailingBlanks, keywordsScore: $keywordsScore, keywordsThreshold: $keywordsThreshold, keywordsFile: $keywordsFile, keywordsBuf: $keywordsBuf, keywordsBufSize: $keywordsBufSize)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'feat': feat.toJson(),
+        'model': model.toJson(),
+        'maxActivePaths': maxActivePaths,
+        'numTrailingBlanks': numTrailingBlanks,
+        'keywordsScore': keywordsScore,
+        'keywordsThreshold': keywordsThreshold,
+        'keywordsFile': keywordsFile,
+        'keywordsBuf': keywordsBuf,
+        'keywordsBufSize': keywordsBufSize,
+      };
+
   final FeatureConfig feat;
   final OnlineModelConfig model;
 
@@ -44,11 +73,21 @@ class KeywordSpotterConfig {
 class KeywordResult {
   KeywordResult({required this.keyword});
 
+  factory KeywordResult.fromJson(Map<String, dynamic> json) {
+    return KeywordResult(
+      keyword: json['keyword'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'KeywordResult(keyword: $keyword)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'keyword': keyword,
+      };
+
   final String keyword;
 }
 
diff --git a/flutter/sherpa_onnx/lib/src/offline_punctuation.dart b/flutter/sherpa_onnx/lib/src/offline_punctuation.dart
index dd38a244..a50073e0 100644
--- a/flutter/sherpa_onnx/lib/src/offline_punctuation.dart
+++ b/flutter/sherpa_onnx/lib/src/offline_punctuation.dart
@@ -11,11 +11,27 @@ class OfflinePunctuationModelConfig {
       this.provider = 'cpu',
       this.debug = true});
 
+  factory OfflinePunctuationModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflinePunctuationModelConfig(
+      ctTransformer: json['ctTransformer'] as String,
+      numThreads: json['numThreads'] as int? ?? 1,
+      provider: json['provider'] as String? ?? 'cpu',
+      debug: json['debug'] as bool? ?? true,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflinePunctuationModelConfig(ctTransformer: $ctTransformer, numThreads: $numThreads, provider: $provider, debug: $debug)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'ctTransformer': ctTransformer,
+        'numThreads': numThreads,
+        'provider': provider,
+        'debug': debug,
+      };
+
   final String ctTransformer;
   final int numThreads;
   final String provider;
@@ -27,11 +43,22 @@ class OfflinePunctuationConfig {
     required this.model,
   });
 
+  factory OfflinePunctuationConfig.fromJson(Map<String, dynamic> json) {
+    return OfflinePunctuationConfig(
+      model: OfflinePunctuationModelConfig.fromJson(
+          json['model'] as Map<String, dynamic>),
+    );
+  }
+
   @override
   String toString() {
     return 'OfflinePunctuationConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model.toJson(),
+      };
+
   final OfflinePunctuationModelConfig model;
 }
 
diff --git a/flutter/sherpa_onnx/lib/src/offline_recognizer.dart b/flutter/sherpa_onnx/lib/src/offline_recognizer.dart
index e7a68845..e7bbaf8c 100644
--- a/flutter/sherpa_onnx/lib/src/offline_recognizer.dart
+++ b/flutter/sherpa_onnx/lib/src/offline_recognizer.dart
@@ -16,11 +16,25 @@ class OfflineTransducerModelConfig {
     this.joiner = '',
   });
 
+  factory OfflineTransducerModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTransducerModelConfig(
+      encoder: json['encoder'] as String? ?? '',
+      decoder: json['decoder'] as String? ?? '',
+      joiner: json['joiner'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTransducerModelConfig(encoder: $encoder, decoder: $decoder, joiner: $joiner)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'encoder': encoder,
+        'decoder': decoder,
+        'joiner': joiner,
+      };
+
   final String encoder;
   final String decoder;
   final String joiner;
@@ -29,22 +43,42 @@ class OfflineTransducerModelConfig {
 class OfflineParaformerModelConfig {
   const OfflineParaformerModelConfig({this.model = ''});
 
+  factory OfflineParaformerModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineParaformerModelConfig(
+      model: json['model'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineParaformerModelConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+      };
+
   final String model;
 }
 
 class OfflineNemoEncDecCtcModelConfig {
   const OfflineNemoEncDecCtcModelConfig({this.model = ''});
 
+  factory OfflineNemoEncDecCtcModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineNemoEncDecCtcModelConfig(
+      model: json['model'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineNemoEncDecCtcModelConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+      };
+
   final String model;
 }
 
@@ -56,11 +90,29 @@ class OfflineWhisperModelConfig {
       this.task = '',
       this.tailPaddings = -1});
 
+  factory OfflineWhisperModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineWhisperModelConfig(
+      encoder: json['encoder'] as String? ?? '',
+      decoder: json['decoder'] as String? ?? '',
+      language: json['language'] as String? ?? '',
+      task: json['task'] as String? ?? '',
+      tailPaddings: json['tailPaddings'] as int? ?? -1,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineWhisperModelConfig(encoder: $encoder, decoder: $decoder, language: $language, task: $task, tailPaddings: $tailPaddings)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'encoder': encoder,
+        'decoder': decoder,
+        'language': language,
+        'task': task,
+        'tailPaddings': tailPaddings,
+      };
+
   final String encoder;
   final String decoder;
   final String language;
@@ -69,15 +121,25 @@ class OfflineWhisperModelConfig {
 }
 
 class OfflineFireRedAsrModelConfig {
-  const OfflineFireRedAsrModelConfig(
-      {this.encoder = '',
-      this.decoder = ''});
+  const OfflineFireRedAsrModelConfig({this.encoder = '', this.decoder = ''});
+
+  factory OfflineFireRedAsrModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineFireRedAsrModelConfig(
+      encoder: json['encoder'] as String? ?? '',
+      decoder: json['decoder'] as String? ?? '',
+    );
+  }
 
   @override
   String toString() {
     return 'OfflineFireRedAsrModelConfig(encoder: $encoder, decoder: $decoder)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'encoder': encoder,
+        'decoder': decoder,
+      };
+
   final String encoder;
   final String decoder;
 }
@@ -89,11 +151,27 @@ class OfflineMoonshineModelConfig {
       this.uncachedDecoder = '',
       this.cachedDecoder = ''});
 
+  factory OfflineMoonshineModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineMoonshineModelConfig(
+      preprocessor: json['preprocessor'] as String? ?? '',
+      encoder: json['encoder'] as String? ?? '',
+      uncachedDecoder: json['uncachedDecoder'] as String? ?? '',
+      cachedDecoder: json['cachedDecoder'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineMoonshineModelConfig(preprocessor: $preprocessor, encoder: $encoder, uncachedDecoder: $uncachedDecoder, cachedDecoder: $cachedDecoder)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'preprocessor': preprocessor,
+        'encoder': encoder,
+        'uncachedDecoder': uncachedDecoder,
+        'cachedDecoder': cachedDecoder,
+      };
+
   final String preprocessor;
   final String encoder;
   final String uncachedDecoder;
@@ -103,11 +181,21 @@ class OfflineMoonshineModelConfig {
 class OfflineTdnnModelConfig {
   const OfflineTdnnModelConfig({this.model = ''});
 
+  factory OfflineTdnnModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTdnnModelConfig(
+      model: json['model'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTdnnModelConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+      };
+
   final String model;
 }
 
@@ -118,11 +206,26 @@ class OfflineSenseVoiceModelConfig {
     this.useInverseTextNormalization = false,
   });
 
+  factory OfflineSenseVoiceModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineSenseVoiceModelConfig(
+      model: json['model'] as String? ?? '',
+      language: json['language'] as String? ?? '',
+      useInverseTextNormalization:
+          json['useInverseTextNormalization'] as bool? ?? false,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineSenseVoiceModelConfig(model: $model, language: $language, useInverseTextNormalization: $useInverseTextNormalization)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+        'language': language,
+        'useInverseTextNormalization': useInverseTextNormalization,
+      };
+
   final String model;
   final String language;
   final bool useInverseTextNormalization;
@@ -131,11 +234,23 @@ class OfflineSenseVoiceModelConfig {
 class OfflineLMConfig {
   const OfflineLMConfig({this.model = '', this.scale = 1.0});
 
+  factory OfflineLMConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineLMConfig(
+      model: json['model'] as String? ?? '',
+      scale: (json['scale'] as num?)?.toDouble() ?? 1.0,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineLMConfig(model: $model, scale: $scale)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+        'scale': scale,
+      };
+
   final String model;
   final double scale;
 }
@@ -160,11 +275,75 @@ class OfflineModelConfig {
     this.telespeechCtc = '',
   });
 
+  factory OfflineModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineModelConfig(
+      transducer: json['transducer'] != null
+          ? OfflineTransducerModelConfig.fromJson(
+              json['transducer'] as Map<String, dynamic>)
+          : const OfflineTransducerModelConfig(),
+      paraformer: json['paraformer'] != null
+          ? OfflineParaformerModelConfig.fromJson(
+              json['paraformer'] as Map<String, dynamic>)
+          : const OfflineParaformerModelConfig(),
+      nemoCtc: json['nemoCtc'] != null
+          ? OfflineNemoEncDecCtcModelConfig.fromJson(
+              json['nemoCtc'] as Map<String, dynamic>)
+          : const OfflineNemoEncDecCtcModelConfig(),
+      whisper: json['whisper'] != null
+          ? OfflineWhisperModelConfig.fromJson(
+              json['whisper'] as Map<String, dynamic>)
+          : const OfflineWhisperModelConfig(),
+      tdnn: json['tdnn'] != null
+          ? OfflineTdnnModelConfig.fromJson(
+              json['tdnn'] as Map<String, dynamic>)
+          : const OfflineTdnnModelConfig(),
+      senseVoice: json['senseVoice'] != null
+          ? OfflineSenseVoiceModelConfig.fromJson(
+              json['senseVoice'] as Map<String, dynamic>)
+          : const OfflineSenseVoiceModelConfig(),
+      moonshine: json['moonshine'] != null
+          ? OfflineMoonshineModelConfig.fromJson(
+              json['moonshine'] as Map<String, dynamic>)
+          : const OfflineMoonshineModelConfig(),
+      fireRedAsr: json['fireRedAsr'] != null
+          ? OfflineFireRedAsrModelConfig.fromJson(
+              json['fireRedAsr'] as Map<String, dynamic>)
+          : const OfflineFireRedAsrModelConfig(),
+      tokens: json['tokens'] as String,
+      numThreads: json['numThreads'] as int? ?? 1,
+      debug: json['debug'] as bool? ?? true,
+      provider: json['provider'] as String? ?? 'cpu',
+      modelType: json['modelType'] as String? ?? '',
+      modelingUnit: json['modelingUnit'] as String? ?? '',
+      bpeVocab: json['bpeVocab'] as String? ?? '',
+      telespeechCtc: json['telespeechCtc'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineModelConfig(transducer: $transducer, paraformer: $paraformer, nemoCtc: $nemoCtc, whisper: $whisper, tdnn: $tdnn, senseVoice: $senseVoice, moonshine: $moonshine, fireRedAsr: $fireRedAsr, tokens: $tokens, numThreads: $numThreads, debug: $debug, provider: $provider, modelType: $modelType, modelingUnit: $modelingUnit, bpeVocab: $bpeVocab, telespeechCtc: $telespeechCtc)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'transducer': transducer.toJson(),
+        'paraformer': paraformer.toJson(),
+        'nemoCtc': nemoCtc.toJson(),
+        'whisper': whisper.toJson(),
+        'tdnn': tdnn.toJson(),
+        'senseVoice': senseVoice.toJson(),
+        'moonshine': moonshine.toJson(),
+        'fireRedAsr': fireRedAsr.toJson(),
+        'tokens': tokens,
+        'numThreads': numThreads,
+        'debug': debug,
+        'provider': provider,
+        'modelType': modelType,
+        'modelingUnit': modelingUnit,
+        'bpeVocab': bpeVocab,
+        'telespeechCtc': telespeechCtc,
+      };
+
   final OfflineTransducerModelConfig transducer;
   final OfflineParaformerModelConfig paraformer;
   final OfflineNemoEncDecCtcModelConfig nemoCtc;
@@ -198,11 +377,43 @@ class OfflineRecognizerConfig {
     this.blankPenalty = 0.0,
   });
 
+  factory OfflineRecognizerConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineRecognizerConfig(
+      feat: json['feat'] != null
+          ? FeatureConfig.fromJson(json['feat'] as Map<String, dynamic>)
+          : const FeatureConfig(),
+      model: OfflineModelConfig.fromJson(json['model'] as Map<String, dynamic>),
+      lm: json['lm'] != null
+          ? OfflineLMConfig.fromJson(json['lm'] as Map<String, dynamic>)
+          : const OfflineLMConfig(),
+      decodingMethod: json['decodingMethod'] as String? ?? 'greedy_search',
+      maxActivePaths: json['maxActivePaths'] as int? ?? 4,
+      hotwordsFile: json['hotwordsFile'] as String? ?? '',
+      hotwordsScore: (json['hotwordsScore'] as num?)?.toDouble() ?? 1.5,
+      ruleFsts: json['ruleFsts'] as String? ?? '',
+      ruleFars: json['ruleFars'] as String? ?? '',
+      blankPenalty: (json['blankPenalty'] as num?)?.toDouble() ?? 0.0,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineRecognizerConfig(feat: $feat, model: $model, lm: $lm, decodingMethod: $decodingMethod, maxActivePaths: $maxActivePaths, hotwordsFile: $hotwordsFile, hotwordsScore: $hotwordsScore, ruleFsts: $ruleFsts, ruleFars: $ruleFars, blankPenalty: $blankPenalty)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'feat': feat.toJson(),
+        'model': model.toJson(),
+        'lm': lm.toJson(),
+        'decodingMethod': decodingMethod,
+        'maxActivePaths': maxActivePaths,
+        'hotwordsFile': hotwordsFile,
+        'hotwordsScore': hotwordsScore,
+        'ruleFsts': ruleFsts,
+        'ruleFars': ruleFars,
+        'blankPenalty': blankPenalty,
+      };
+
   final FeatureConfig feat;
   final OfflineModelConfig model;
   final OfflineLMConfig lm;
@@ -229,11 +440,34 @@ class OfflineRecognizerResult {
       required this.emotion,
       required this.event});
 
+  factory OfflineRecognizerResult.fromJson(Map<String, dynamic> json) {
+    return OfflineRecognizerResult(
+      text: json['text'] as String? ?? '',
+      tokens: (json['tokens'] as List?)?.map((e) => e as String).toList() ?? [],
+      timestamps: (json['timestamps'] as List?)
+              ?.map((e) => (e as num).toDouble())
+              .toList() ??
+          [],
+      lang: json['lang'] as String? ?? '',
+      emotion: json['emotion'] as String? ?? '',
+      event: json['event'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineRecognizerResult(text: $text, tokens: $tokens, timestamps: $timestamps, lang: $lang, emotion: $emotion, event: $event)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'text': text,
+        'tokens': tokens,
+        'timestamps': timestamps,
+        'lang': lang,
+        'emotion': emotion,
+        'event': event,
+      };
+
   final String text;
   final List<String> tokens;
   final List<double> timestamps;
@@ -305,8 +539,10 @@ class OfflineRecognizer {
         config.model.moonshine.cachedDecoder.toNativeUtf8();
 
     // FireRedAsr
-    c.ref.model.fireRedAsr.encoder = config.model.fireRedAsr.encoder.toNativeUtf8();
-    c.ref.model.fireRedAsr.decoder = config.model.fireRedAsr.decoder.toNativeUtf8();
+    c.ref.model.fireRedAsr.encoder =
+        config.model.fireRedAsr.encoder.toNativeUtf8();
+    c.ref.model.fireRedAsr.decoder =
+        config.model.fireRedAsr.decoder.toNativeUtf8();
 
     c.ref.model.tokens = config.model.tokens.toNativeUtf8();
 
diff --git a/flutter/sherpa_onnx/lib/src/offline_speaker_diarization.dart b/flutter/sherpa_onnx/lib/src/offline_speaker_diarization.dart
index fe046a16..6ee72f9f 100644
--- a/flutter/sherpa_onnx/lib/src/offline_speaker_diarization.dart
+++ b/flutter/sherpa_onnx/lib/src/offline_speaker_diarization.dart
@@ -14,11 +14,25 @@ class OfflineSpeakerDiarizationSegment {
     required this.speaker,
   });
 
+  factory OfflineSpeakerDiarizationSegment.fromJson(Map<String, dynamic> json) {
+    return OfflineSpeakerDiarizationSegment(
+      start: (json['start'] as num).toDouble(),
+      end: (json['end'] as num).toDouble(),
+      speaker: json['speaker'] as int,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineSpeakerDiarizationSegment(start: $start, end: $end, speaker: $speaker)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'start': start,
+        'end': end,
+        'speaker': speaker,
+      };
+
   final double start;
   final double end;
   final int speaker;
@@ -29,11 +43,22 @@ class OfflineSpeakerSegmentationPyannoteModelConfig {
     this.model = '',
   });
 
+  factory OfflineSpeakerSegmentationPyannoteModelConfig.fromJson(
+      Map<String, dynamic> json) {
+    return OfflineSpeakerSegmentationPyannoteModelConfig(
+      model: json['model'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineSpeakerSegmentationPyannoteModelConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+      };
+
   final String model;
 }
 
@@ -45,11 +70,31 @@ class OfflineSpeakerSegmentationModelConfig {
     this.provider = 'cpu',
   });
 
+  factory OfflineSpeakerSegmentationModelConfig.fromJson(
+      Map<String, dynamic> json) {
+    return OfflineSpeakerSegmentationModelConfig(
+      pyannote: json['pyannote'] != null
+          ? OfflineSpeakerSegmentationPyannoteModelConfig.fromJson(
+              json['pyannote'] as Map<String, dynamic>)
+          : const OfflineSpeakerSegmentationPyannoteModelConfig(),
+      numThreads: json['numThreads'] as int? ?? 1,
+      debug: json['debug'] as bool? ?? true,
+      provider: json['provider'] as String? ?? 'cpu',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineSpeakerSegmentationModelConfig(pyannote: $pyannote, numThreads: $numThreads, debug: $debug, provider: $provider)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'pyannote': pyannote.toJson(),
+        'numThreads': numThreads,
+        'debug': debug,
+        'provider': provider,
+      };
+
   final OfflineSpeakerSegmentationPyannoteModelConfig pyannote;
 
   final int numThreads;
@@ -63,11 +108,23 @@ class FastClusteringConfig {
     this.threshold = 0.5,
   });
 
+  factory FastClusteringConfig.fromJson(Map<String, dynamic> json) {
+    return FastClusteringConfig(
+      numClusters: json['numClusters'] as int? ?? -1,
+      threshold: (json['threshold'] as num?)?.toDouble() ?? 0.5,
+    );
+  }
+
   @override
   String toString() {
     return 'FastClusteringConfig(numClusters: $numClusters, threshold: $threshold)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'numClusters': numClusters,
+        'threshold': threshold,
+      };
+
   final int numClusters;
   final double threshold;
 }
@@ -81,11 +138,38 @@ class OfflineSpeakerDiarizationConfig {
     this.minDurationOff = 0.5,
   });
 
+  factory OfflineSpeakerDiarizationConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineSpeakerDiarizationConfig(
+      segmentation: json['segmentation'] != null
+          ? OfflineSpeakerSegmentationModelConfig.fromJson(
+              json['segmentation'] as Map<String, dynamic>)
+          : const OfflineSpeakerSegmentationModelConfig(),
+      embedding: json['embedding'] != null
+          ? SpeakerEmbeddingExtractorConfig.fromJson(
+              json['embedding'] as Map<String, dynamic>)
+          : const SpeakerEmbeddingExtractorConfig(model: ''),
+      clustering: json['clustering'] != null
+          ? FastClusteringConfig.fromJson(
+              json['clustering'] as Map<String, dynamic>)
+          : const FastClusteringConfig(),
+      minDurationOn: (json['minDurationOn'] as num?)?.toDouble() ?? 0.2,
+      minDurationOff: (json['minDurationOff'] as num?)?.toDouble() ?? 0.5,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineSpeakerDiarizationConfig(segmentation: $segmentation, embedding: $embedding, clustering: $clustering, minDurationOn: $minDurationOn, minDurationOff: $minDurationOff)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'segmentation': segmentation.toJson(),
+        'embedding': embedding.toJson(),
+        'clustering': clustering.toJson(),
+        'minDurationOn': minDurationOn,
+        'minDurationOff': minDurationOff,
+      };
+
   final OfflineSpeakerSegmentationModelConfig segmentation;
   final SpeakerEmbeddingExtractorConfig embedding;
   final FastClusteringConfig clustering;
diff --git a/flutter/sherpa_onnx/lib/src/online_punctuation.dart b/flutter/sherpa_onnx/lib/src/online_punctuation.dart
index 118be8f5..85ada985 100644
--- a/flutter/sherpa_onnx/lib/src/online_punctuation.dart
+++ b/flutter/sherpa_onnx/lib/src/online_punctuation.dart
@@ -11,6 +11,16 @@ class OnlinePunctuationModelConfig {
       this.provider = 'cpu',
       this.debug = true});
 
+  factory OnlinePunctuationModelConfig.fromJson(Map<String, dynamic> json) {
+    return OnlinePunctuationModelConfig(
+      cnnBiLstm: json['cnnBiLstm'],
+      bpeVocab: json['bpeVocab'],
+      numThreads: json['numThreads'],
+      provider: json['provider'],
+      debug: json['debug'],
+    );
+  }
+
   @override
   String toString() {
     return 'OnlinePunctuationModelConfig(cnnBiLstm: $cnnBiLstm, '
@@ -18,6 +28,16 @@ class OnlinePunctuationModelConfig {
         'provider: $provider, debug: $debug)';
   }
 
+  Map<String, dynamic> toJson() {
+    return {
+      'cnnBiLstm': cnnBiLstm,
+      'bpeVocab': bpeVocab,
+      'numThreads': numThreads,
+      'provider': provider,
+      'debug': debug,
+    };
+  }
+
   final String cnnBiLstm;
   final String bpeVocab;
   final int numThreads;
@@ -30,11 +50,23 @@ class OnlinePunctuationConfig {
     required this.model,
   });
 
+  factory OnlinePunctuationConfig.fromJson(Map<String, dynamic> json) {
+    return OnlinePunctuationConfig(
+      model: OnlinePunctuationModelConfig.fromJson(json['model']),
+    );
+  }
+
   @override
   String toString() {
     return 'OnlinePunctuationConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() {
+    return {
+      'model': model.toJson(),
+    };
+  }
+
   final OnlinePunctuationModelConfig model;
 }
 
@@ -90,7 +122,7 @@ class OnlinePunctuation {
     final ans = p.toDartString();
 
     SherpaOnnxBindings.sherpaOnnxOnlinePunctuationFreeText?.call(p);
-    
+
     return ans;
   }
 
diff --git a/flutter/sherpa_onnx/lib/src/online_recognizer.dart b/flutter/sherpa_onnx/lib/src/online_recognizer.dart
index 69ed9389..4a4959c9 100644
--- a/flutter/sherpa_onnx/lib/src/online_recognizer.dart
+++ b/flutter/sherpa_onnx/lib/src/online_recognizer.dart
@@ -16,11 +16,25 @@ class OnlineTransducerModelConfig {
     this.joiner = '',
   });
 
+  factory OnlineTransducerModelConfig.fromJson(Map<String, dynamic> json) {
+    return OnlineTransducerModelConfig(
+      encoder: json['encoder'] as String? ?? '',
+      decoder: json['decoder'] as String? ?? '',
+      joiner: json['joiner'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineTransducerModelConfig(encoder: $encoder, decoder: $decoder, joiner: $joiner)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'encoder': encoder,
+        'decoder': decoder,
+        'joiner': joiner,
+      };
+
   final String encoder;
   final String decoder;
   final String joiner;
@@ -29,11 +43,23 @@ class OnlineTransducerModelConfig {
 class OnlineParaformerModelConfig {
   const OnlineParaformerModelConfig({this.encoder = '', this.decoder = ''});
 
+  factory OnlineParaformerModelConfig.fromJson(Map<String, dynamic> json) {
+    return OnlineParaformerModelConfig(
+      encoder: json['encoder'] as String? ?? '',
+      decoder: json['decoder'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineParaformerModelConfig(encoder: $encoder, decoder: $decoder)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'encoder': encoder,
+        'decoder': decoder,
+      };
+
   final String encoder;
   final String decoder;
 }
@@ -41,11 +67,21 @@ class OnlineParaformerModelConfig {
 class OnlineZipformer2CtcModelConfig {
   const OnlineZipformer2CtcModelConfig({this.model = ''});
 
+  factory OnlineZipformer2CtcModelConfig.fromJson(Map<String, dynamic> json) {
+    return OnlineZipformer2CtcModelConfig(
+      model: json['model'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineZipformer2CtcModelConfig(model: $model)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+      };
+
   final String model;
 }
 
@@ -63,11 +99,42 @@ class OnlineModelConfig {
     this.bpeVocab = '',
   });
 
+  factory OnlineModelConfig.fromJson(Map<String, dynamic> json) {
+    return OnlineModelConfig(
+      transducer: OnlineTransducerModelConfig.fromJson(
+          json['transducer'] as Map<String, dynamic>? ?? const {}),
+      paraformer: OnlineParaformerModelConfig.fromJson(
+          json['paraformer'] as Map<String, dynamic>? ?? const {}),
+      zipformer2Ctc: OnlineZipformer2CtcModelConfig.fromJson(
+          json['zipformer2Ctc'] as Map<String, dynamic>? ?? const {}),
+      tokens: json['tokens'] as String,
+      numThreads: json['numThreads'] as int? ?? 1,
+      provider: json['provider'] as String? ?? 'cpu',
+      debug: json['debug'] as bool? ?? true,
+      modelType: json['modelType'] as String? ?? '',
+      modelingUnit: json['modelingUnit'] as String? ?? '',
+      bpeVocab: json['bpeVocab'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineModelConfig(transducer: $transducer, paraformer: $paraformer, zipformer2Ctc: $zipformer2Ctc, tokens: $tokens, numThreads: $numThreads, provider: $provider, debug: $debug, modelType: $modelType, modelingUnit: $modelingUnit, bpeVocab: $bpeVocab)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'transducer': transducer.toJson(),
+        'paraformer': paraformer.toJson(),
+        'zipformer2Ctc': zipformer2Ctc.toJson(),
+        'tokens': tokens,
+        'numThreads': numThreads,
+        'provider': provider,
+        'debug': debug,
+        'modelType': modelType,
+        'modelingUnit': modelingUnit,
+        'bpeVocab': bpeVocab,
+      };
+
   final OnlineTransducerModelConfig transducer;
   final OnlineParaformerModelConfig paraformer;
   final OnlineZipformer2CtcModelConfig zipformer2Ctc;
@@ -90,11 +157,23 @@ class OnlineModelConfig {
 class OnlineCtcFstDecoderConfig {
   const OnlineCtcFstDecoderConfig({this.graph = '', this.maxActive = 3000});
 
+  factory OnlineCtcFstDecoderConfig.fromJson(Map<String, dynamic> json) {
+    return OnlineCtcFstDecoderConfig(
+      graph: json['graph'] as String? ?? '',
+      maxActive: json['maxActive'] as int? ?? 3000,
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineCtcFstDecoderConfig(graph: $graph, maxActive: $maxActive)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'graph': graph,
+        'maxActive': maxActive,
+      };
+
   final String graph;
   final int maxActive;
 }
@@ -117,11 +196,52 @@ class OnlineRecognizerConfig {
     this.blankPenalty = 0.0,
   });
 
+  factory OnlineRecognizerConfig.fromJson(Map<String, dynamic> json) {
+    return OnlineRecognizerConfig(
+      feat: FeatureConfig.fromJson(
+          json['feat'] as Map<String, dynamic>? ?? const {}),
+      model: OnlineModelConfig.fromJson(json['model'] as Map<String, dynamic>),
+      decodingMethod: json['decodingMethod'] as String? ?? 'greedy_search',
+      maxActivePaths: json['maxActivePaths'] as int? ?? 4,
+      enableEndpoint: json['enableEndpoint'] as bool? ?? true,
+      rule1MinTrailingSilence:
+          (json['rule1MinTrailingSilence'] as num?)?.toDouble() ?? 2.4,
+      rule2MinTrailingSilence:
+          (json['rule2MinTrailingSilence'] as num?)?.toDouble() ?? 1.2,
+      rule3MinUtteranceLength:
+          (json['rule3MinUtteranceLength'] as num?)?.toDouble() ?? 20.0,
+      hotwordsFile: json['hotwordsFile'] as String? ?? '',
+      hotwordsScore: (json['hotwordsScore'] as num?)?.toDouble() ?? 1.5,
+      ctcFstDecoderConfig: OnlineCtcFstDecoderConfig.fromJson(
+          json['ctcFstDecoderConfig'] as Map<String, dynamic>? ?? const {}),
+      ruleFsts: json['ruleFsts'] as String? ?? '',
+      ruleFars: json['ruleFars'] as String? ?? '',
+      blankPenalty: (json['blankPenalty'] as num?)?.toDouble() ?? 0.0,
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineRecognizerConfig(feat: $feat, model: $model, decodingMethod: $decodingMethod, maxActivePaths: $maxActivePaths, enableEndpoint: $enableEndpoint, rule1MinTrailingSilence: $rule1MinTrailingSilence, rule2MinTrailingSilence: $rule2MinTrailingSilence, rule3MinUtteranceLength: $rule3MinUtteranceLength, hotwordsFile: $hotwordsFile, hotwordsScore: $hotwordsScore, ctcFstDecoderConfig: $ctcFstDecoderConfig, ruleFsts: $ruleFsts, ruleFars: $ruleFars, blankPenalty: $blankPenalty)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'feat': feat.toJson(),
+        'model': model.toJson(),
+        'decodingMethod': decodingMethod,
+        'maxActivePaths': maxActivePaths,
+        'enableEndpoint': enableEndpoint,
+        'rule1MinTrailingSilence': rule1MinTrailingSilence,
+        'rule2MinTrailingSilence': rule2MinTrailingSilence,
+        'rule3MinUtteranceLength': rule3MinUtteranceLength,
+        'hotwordsFile': hotwordsFile,
+        'hotwordsScore': hotwordsScore,
+        'ctcFstDecoderConfig': ctcFstDecoderConfig.toJson(),
+        'ruleFsts': ruleFsts,
+        'ruleFars': ruleFars,
+        'blankPenalty': blankPenalty,
+      };
+
   final FeatureConfig feat;
   final OnlineModelConfig model;
   final String decodingMethod;
@@ -151,11 +271,27 @@ class OnlineRecognizerResult {
   OnlineRecognizerResult(
       {required this.text, required this.tokens, required this.timestamps});
 
+  factory OnlineRecognizerResult.fromJson(Map<String, dynamic> json) {
+    return OnlineRecognizerResult(
+      text: json['text'] as String,
+      tokens: List<String>.from(json['tokens'] as List),
+      timestamps: (json['timestamps'] as List)
+          .map<double>((e) => (e as num).toDouble())
+          .toList(),
+    );
+  }
+
   @override
   String toString() {
     return 'OnlineRecognizerResult(text: $text, tokens: $tokens, timestamps: $timestamps)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'text': text,
+        'tokens': tokens,
+        'timestamps': timestamps,
+      };
+
   final String text;
   final List<String> tokens;
   final List<double> timestamps;
diff --git a/flutter/sherpa_onnx/lib/src/speaker_identification.dart b/flutter/sherpa_onnx/lib/src/speaker_identification.dart
index 8b27dbc6..7fc13906 100644
--- a/flutter/sherpa_onnx/lib/src/speaker_identification.dart
+++ b/flutter/sherpa_onnx/lib/src/speaker_identification.dart
@@ -13,11 +13,27 @@ class SpeakerEmbeddingExtractorConfig {
       this.debug = true,
       this.provider = 'cpu'});
 
+  factory SpeakerEmbeddingExtractorConfig.fromJson(Map<String, dynamic> json) {
+    return SpeakerEmbeddingExtractorConfig(
+      model: json['model'] as String,
+      numThreads: json['numThreads'] as int? ?? 1,
+      debug: json['debug'] as bool? ?? true,
+      provider: json['provider'] as String? ?? 'cpu',
+    );
+  }
+
   @override
   String toString() {
     return 'SpeakerEmbeddingExtractorConfig(model: $model, numThreads: $numThreads, debug: $debug, provider: $provider)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+        'numThreads': numThreads,
+        'debug': debug,
+        'provider': provider,
+      };
+
   final String model;
   final int numThreads;
   final bool debug;
diff --git a/flutter/sherpa_onnx/lib/src/tts.dart b/flutter/sherpa_onnx/lib/src/tts.dart
index a74690e7..d3099944 100644
--- a/flutter/sherpa_onnx/lib/src/tts.dart
+++ b/flutter/sherpa_onnx/lib/src/tts.dart
@@ -18,11 +18,35 @@ class OfflineTtsVitsModelConfig {
     this.dictDir = '',
   });
 
+  factory OfflineTtsVitsModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTtsVitsModelConfig(
+      model: json['model'] as String? ?? '',
+      lexicon: json['lexicon'] as String? ?? '',
+      tokens: json['tokens'] as String? ?? '',
+      dataDir: json['dataDir'] as String? ?? '',
+      noiseScale: (json['noiseScale'] as num?)?.toDouble() ?? 0.667,
+      noiseScaleW: (json['noiseScaleW'] as num?)?.toDouble() ?? 0.8,
+      lengthScale: (json['lengthScale'] as num?)?.toDouble() ?? 1.0,
+      dictDir: json['dictDir'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTtsVitsModelConfig(model: $model, lexicon: $lexicon, tokens: $tokens, dataDir: $dataDir, noiseScale: $noiseScale, noiseScaleW: $noiseScaleW, lengthScale: $lengthScale, dictDir: $dictDir)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+        'lexicon': lexicon,
+        'tokens': tokens,
+        'dataDir': dataDir,
+        'noiseScale': noiseScale,
+        'noiseScaleW': noiseScaleW,
+        'lengthScale': lengthScale,
+        'dictDir': dictDir,
+      };
+
   final String model;
   final String lexicon;
   final String tokens;
@@ -45,11 +69,35 @@ class OfflineTtsMatchaModelConfig {
     this.dictDir = '',
   });
 
+  factory OfflineTtsMatchaModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTtsMatchaModelConfig(
+      acousticModel: json['acousticModel'] as String? ?? '',
+      vocoder: json['vocoder'] as String? ?? '',
+      lexicon: json['lexicon'] as String? ?? '',
+      tokens: json['tokens'] as String? ?? '',
+      dataDir: json['dataDir'] as String? ?? '',
+      noiseScale: (json['noiseScale'] as num?)?.toDouble() ?? 0.667,
+      lengthScale: (json['lengthScale'] as num?)?.toDouble() ?? 1.0,
+      dictDir: json['dictDir'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTtsMatchaModelConfig(acousticModel: $acousticModel, vocoder: $vocoder, lexicon: $lexicon, tokens: $tokens, dataDir: $dataDir, noiseScale: $noiseScale, lengthScale: $lengthScale, dictDir: $dictDir)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'acousticModel': acousticModel,
+        'vocoder': vocoder,
+        'lexicon': lexicon,
+        'tokens': tokens,
+        'dataDir': dataDir,
+        'noiseScale': noiseScale,
+        'lengthScale': lengthScale,
+        'dictDir': dictDir,
+      };
+
   final String acousticModel;
   final String vocoder;
   final String lexicon;
@@ -71,11 +119,33 @@ class OfflineTtsKokoroModelConfig {
     this.lexicon = '',
   });
 
+  factory OfflineTtsKokoroModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTtsKokoroModelConfig(
+      model: json['model'] as String? ?? '',
+      voices: json['voices'] as String? ?? '',
+      tokens: json['tokens'] as String? ?? '',
+      dataDir: json['dataDir'] as String? ?? '',
+      lengthScale: (json['lengthScale'] as num?)?.toDouble() ?? 1.0,
+      dictDir: json['dictDir'] as String? ?? '',
+      lexicon: json['lexicon'] as String? ?? '',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTtsKokoroModelConfig(model: $model, voices: $voices, tokens: $tokens, dataDir: $dataDir, lengthScale: $lengthScale, dictDir: $dictDir, lexicon: $lexicon)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+        'voices': voices,
+        'tokens': tokens,
+        'dataDir': dataDir,
+        'lengthScale': lengthScale,
+        'dictDir': dictDir,
+        'lexicon': lexicon,
+      };
+
   final String model;
   final String voices;
   final String tokens;
@@ -95,11 +165,34 @@ class OfflineTtsModelConfig {
     this.provider = 'cpu',
   });
 
+  factory OfflineTtsModelConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTtsModelConfig(
+      vits: OfflineTtsVitsModelConfig.fromJson(
+          json['vits'] as Map<String, dynamic>? ?? const {}),
+      matcha: OfflineTtsMatchaModelConfig.fromJson(
+          json['matcha'] as Map<String, dynamic>? ?? const {}),
+      kokoro: OfflineTtsKokoroModelConfig.fromJson(
+          json['kokoro'] as Map<String, dynamic>? ?? const {}),
+      numThreads: json['numThreads'] as int? ?? 1,
+      debug: json['debug'] as bool? ?? true,
+      provider: json['provider'] as String? ?? 'cpu',
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTtsModelConfig(vits: $vits, matcha: $matcha, kokoro: $kokoro, numThreads: $numThreads, debug: $debug, provider: $provider)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'vits': vits.toJson(),
+        'matcha': matcha.toJson(),
+        'kokoro': kokoro.toJson(),
+        'numThreads': numThreads,
+        'debug': debug,
+        'provider': provider,
+      };
+
   final OfflineTtsVitsModelConfig vits;
   final OfflineTtsMatchaModelConfig matcha;
   final OfflineTtsKokoroModelConfig kokoro;
@@ -117,11 +210,30 @@ class OfflineTtsConfig {
     this.silenceScale = 0.2,
   });
 
+  factory OfflineTtsConfig.fromJson(Map<String, dynamic> json) {
+    return OfflineTtsConfig(
+      model:
+          OfflineTtsModelConfig.fromJson(json['model'] as Map<String, dynamic>),
+      ruleFsts: json['ruleFsts'] as String? ?? '',
+      maxNumSenetences: json['maxNumSenetences'] as int? ?? 1,
+      ruleFars: json['ruleFars'] as String? ?? '',
+      silenceScale: (json['silenceScale'] as num?)?.toDouble() ?? 0.2,
+    );
+  }
+
   @override
   String toString() {
     return 'OfflineTtsConfig(model: $model, ruleFsts: $ruleFsts, maxNumSenetences: $maxNumSenetences, ruleFars: $ruleFars, silenceScale: $silenceScale)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model.toJson(),
+        'ruleFsts': ruleFsts,
+        'maxNumSenetences': maxNumSenetences,
+        'ruleFars': ruleFars,
+        'silenceScale': silenceScale,
+      };
+
   final OfflineTtsModelConfig model;
   final String ruleFsts;
   final int maxNumSenetences;
diff --git a/flutter/sherpa_onnx/lib/src/vad.dart b/flutter/sherpa_onnx/lib/src/vad.dart
index 7db0e55e..85937c47 100644
--- a/flutter/sherpa_onnx/lib/src/vad.dart
+++ b/flutter/sherpa_onnx/lib/src/vad.dart
@@ -14,11 +14,33 @@ class SileroVadModelConfig {
       this.windowSize = 512,
       this.maxSpeechDuration = 5.0});
 
+  factory SileroVadModelConfig.fromJson(Map<String, dynamic> json) {
+    return SileroVadModelConfig(
+      model: json['model'] as String? ?? '',
+      threshold: (json['threshold'] as num?)?.toDouble() ?? 0.5,
+      minSilenceDuration:
+          (json['minSilenceDuration'] as num?)?.toDouble() ?? 0.5,
+      minSpeechDuration:
+          (json['minSpeechDuration'] as num?)?.toDouble() ?? 0.25,
+      windowSize: json['windowSize'] as int? ?? 512,
+      maxSpeechDuration: (json['maxSpeechDuration'] as num?)?.toDouble() ?? 5.0,
+    );
+  }
+
   @override
   String toString() {
     return 'SileroVadModelConfig(model: $model, threshold: $threshold, minSilenceDuration: $minSilenceDuration, minSpeechDuration: $minSpeechDuration, windowSize: $windowSize, maxSpeechDuration: $maxSpeechDuration)';
   }
 
+  Map<String, dynamic> toJson() => {
+        'model': model,
+        'threshold': threshold,
+        'minSilenceDuration': minSilenceDuration,
+        'minSpeechDuration': minSpeechDuration,
+        'windowSize': windowSize,
+        'maxSpeechDuration': maxSpeechDuration,
+      };
+
   final String model;
   final double threshold;
   final double minSilenceDuration;
@@ -28,23 +50,43 @@ class SileroVadModelConfig {
 }
 
 class VadModelConfig {
-  VadModelConfig(
-      {this.sileroVad = const SileroVadModelConfig(),
-      this.sampleRate = 16000,
-      this.numThreads = 1,
-      this.provider = 'cpu',
-      this.debug = true});
-
-  @override
-  String toString() {
-    return 'VadModelConfig(sileroVad: $sileroVad, sampleRate: $sampleRate, numThreads: $numThreads, provider: $provider, debug: $debug)';
-  }
+  VadModelConfig({
+    this.sileroVad = const SileroVadModelConfig(),
+    this.sampleRate = 16000,
+    this.numThreads = 1,
+    this.provider = 'cpu',
+    this.debug = true,
+  });
 
   final SileroVadModelConfig sileroVad;
   final int sampleRate;
   final int numThreads;
   final String provider;
   final bool debug;
+
+  factory VadModelConfig.fromJson(Map<String, dynamic> json) {
+    return VadModelConfig(
+      sileroVad: SileroVadModelConfig.fromJson(
+          json['sileroVad'] as Map<String, dynamic>? ?? const {}),
+      sampleRate: json['sampleRate'] as int? ?? 16000,
+      numThreads: json['numThreads'] as int? ?? 1,
+      provider: json['provider'] as String? ?? 'cpu',
+      debug: json['debug'] as bool? ?? true,
+    );
+  }
+
+  Map<String, dynamic> toJson() => {
+        'sileroVad': sileroVad.toJson(),
+        'sampleRate': sampleRate,
+        'numThreads': numThreads,
+        'provider': provider,
+        'debug': debug,
+      };
+
+  @override
+  String toString() {
+    return 'VadModelConfig(sileroVad: $sileroVad, sampleRate: $sampleRate, numThreads: $numThreads, provider: $provider, debug: $debug)';
+  }
 }
 
 class SpeechSegment {