diff --git a/CHANGELOG.md b/CHANGELOG.md
index efa70834..c0d617c6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,7 +18,8 @@
 - Public PluginManager mutability
 
 ### Fixed
-- Proper json array index treatment
+- Proper json array index treatment.
+- Proper json index for single-value array.
 
 ### Security
 ## [0.4.0]
diff --git a/dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/context/Context.kt b/dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/context/Context.kt
index 3c2cf28b..b7e393cf 100644
--- a/dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/context/Context.kt
+++ b/dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/context/Context.kt
@@ -26,7 +26,7 @@ import kotlin.jvm.Synchronized
 public open class Context internal constructor(
     final override val name: Name,
     public val parent: Context?,
-    plugins: Set<Plugin>,
+    plugins: Set<Plugin>, // set of unattached plugins
     meta: Meta,
 ) : Named, MetaRepr, Provider, CoroutineScope {
 
diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt
index 0929a188..ea855ca4 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt
@@ -56,7 +56,7 @@ private fun Meta.toJsonWithIndex(descriptor: NodeDescriptor?, indexValue: String
             }
             1 -> {
                 val (index, item) = items.entries.first()
-                val element = item.toJsonElement(itemDescriptor, null)
+                val element = item.toJsonElement(itemDescriptor, index)
                 if (index == null) {
                     elementMap[jsonKey] = element
                 } else {
diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaBuilder.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaBuilder.kt
index 2f32e187..4574ce4b 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaBuilder.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaBuilder.kt
@@ -2,6 +2,7 @@ package space.kscience.dataforge.meta
 
 import space.kscience.dataforge.misc.DFBuilder
 import space.kscience.dataforge.names.Name
+import space.kscience.dataforge.names.NameToken
 import space.kscience.dataforge.names.asName
 import space.kscience.dataforge.values.EnumValue
 import space.kscience.dataforge.values.Value
@@ -13,6 +14,8 @@ import kotlin.jvm.JvmName
  */
 @DFBuilder
 public class MetaBuilder : AbstractMutableMeta<MetaBuilder>() {
+    override val children: MutableMap<NameToken, TypedMetaItem<MetaBuilder>> = LinkedHashMap()
+
     override fun wrapNode(meta: Meta): MetaBuilder = if (meta is MetaBuilder) meta else meta.toMutableMeta()
     override fun empty(): MetaBuilder = MetaBuilder()
 
diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableMeta.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableMeta.kt
index b54c6534..6a8b0203 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableMeta.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableMeta.kt
@@ -13,10 +13,10 @@ public interface MutableMeta<out M : MutableMeta<M>> : TypedMeta<M>, MutableItem
  * Changes in Meta are not thread safe.
  */
 public abstract class AbstractMutableMeta<M : MutableMeta<M>> : AbstractTypedMeta<M>(), MutableMeta<M> {
-    protected val children: MutableMap<NameToken, TypedMetaItem<M>> = LinkedHashMap()
 
-    override val items: Map<NameToken, TypedMetaItem<M>>
-        get() = children
+    protected abstract val children: MutableMap<NameToken, TypedMetaItem<M>>
+
+    override val items: Map<NameToken, TypedMetaItem<M>> get() = children
 
     //protected abstract fun itemChanged(name: Name, oldItem: MetaItem<*>?, newItem: MetaItem<*>?)
 
diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/TypedMeta.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/TypedMeta.kt
index cd1c3c47..f6f02c70 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/TypedMeta.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/TypedMeta.kt
@@ -39,10 +39,15 @@ public abstract class MetaBase : Meta {
 
     override fun hashCode(): Int = items.hashCode()
 
-    override fun toString(): String = Json {
-        prettyPrint = true
-        useArrayPolymorphism = true
-    }.encodeToString(MetaSerializer, this)
+    override fun toString(): String = json.encodeToString(MetaSerializer, this)
+
+    public companion object{
+        private val json = Json {
+            prettyPrint = true
+            useArrayPolymorphism = true
+        }
+
+    }
 }
 
 /**