The Shared Preferences and Database tools are driven by two small interfaces. The toolkit contains adapters for the storage CARP apps use (shared_preferences and sembast), and you can implement your own interfaces for any other storage.

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Key/value stores

KeyValueStore powers the Preferences tool (inspect / search / edit / add / delete). Pass one or more via DebugToolkitConfig.keyValueStores. 
keyValueStores: [
  SharedPreferencesKeyValueStore(prefs, name: 'CARP Preferences'),
],
SharedPreferencesKeyValueStore hides DebugEnv’s own override keys (carp_debug_env.*) from listing and “clear all” by default, so the inspector never clobbers the launch-argument override store. Customize with hiddenPrefixes:
SharedPreferencesKeyValueStore(prefs, hiddenPrefixes: ['carp_debug_env.', 'flutter.']);

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Custom key/value store

class MyKeyValueStore implements KeyValueStore {
  @override String get name => 'Secure Storage';
  @override Future<List<String>> keys() async => myStore.allKeys();
  @override Future<Object?> read(String key) => myStore.read(key);
  @override Future<void> write(String key, Object value) => myStore.write(key, '$value');
  @override Future<void> delete(String key) => myStore.delete(key);
  @override Future<void> clear() => myStore.deleteAll();
}
Supported value types for write are String, bool, int, double and List<String>.

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Databases

DebugDatabase powers the Database tool (browse stores → records → delete). Pass one or more via DebugToolkitConfig.databases. 
databases: [
  SembastDebugDatabase(db, [
    SembastStoreDescriptor('settings', StoreRef<String, Object?>.main()),
    SembastStoreDescriptor('results', intMapStoreFactory.store('result_store')),
  ]),
],
Because sembast does not enumerate its stores at runtime, you list the StoreRefs you want to inspect. Any key/value types are accepted.

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Custom database

class MyDebugDatabase implements DebugDatabase {
  @override String get name => 'My DB';
  @override List<String> get storeNames => ['users', 'events'];

  @override
  Future<List<DebugRecord>> records(String store) async =>
      (await myDb.query(store)).map((row) => DebugRecord(row.id, row.toMap())).toList();

  @override
  Future<void> deleteRecord(String store, Object key) => myDb.delete(store, key);

  @override
  Future<void> clearStore(String store) => myDb.clear(store);
}