diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f981e24..7dc1eeaa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,14 +5,16 @@
 - Experimental `listOfSpec` delegate.
 
 ### Changed
-- **API breaking** Descriptor no has a member property `defaultValue` instead of `defaultItem()` extension. It cahces default value state on the first call. It is done because computing default on each call is too expensive.
+- **API breaking** Descriptor no has a member property `defaultValue` instead of `defaultItem()` extension. It caches default value state on the first call. It is done because computing default on each call is too expensive.
 - Kotlin 1.5.10
+- Build tools 0.10.0
 
 ### Deprecated
 
 ### Removed
 
 ### Fixed
+- Proper json array index treatment
 
 ### Security
 ## [0.4.0]
diff --git a/build.gradle.kts b/build.gradle.kts
index 8a37909d..c4293377 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -4,7 +4,7 @@ plugins {
 
 allprojects {
     group = "space.kscience"
-    version = "0.4.2"
+    version = "0.4.3"
 }
 
 subprojects {
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 3e708314..0929a188 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
@@ -55,7 +55,16 @@ private fun Meta.toJsonWithIndex(descriptor: NodeDescriptor?, indexValue: String
                 //do nothing
             }
             1 -> {
-                elementMap[jsonKey] = items.values.first().toJsonElement(itemDescriptor, null)
+                val (index, item) = items.entries.first()
+                val element = item.toJsonElement(itemDescriptor, null)
+                if (index == null) {
+                    elementMap[jsonKey] = element
+                } else {
+                    //treat arrays with single element
+                    elementMap[jsonKey] = buildJsonArray {
+                        add(element)
+                    }
+                }
             }
             else -> {
                 val array = buildJsonArray {
diff --git a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableItemProvider.kt b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableItemProvider.kt
index cb901c40..97b1af0f 100644
--- a/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableItemProvider.kt
+++ b/dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableItemProvider.kt
@@ -53,7 +53,7 @@ public fun MutableItemProvider.setIndexedItems(
     val tokens = name.tokens.toMutableList()
     val last = tokens.last()
     items.forEachIndexed { index, meta ->
-        val indexedToken = NameToken(last.body, last.index + indexFactory(meta, index))
+        val indexedToken = NameToken(last.body, (last.index ?: "") + indexFactory(meta, index))
         tokens[tokens.lastIndex] = indexedToken
         set(Name(tokens), meta)
     }
@@ -97,7 +97,6 @@ public fun MutableItemProvider.getChild(childName: Name): MutableItemProvider {
 public fun MutableItemProvider.getChild(childName: String): MutableItemProvider = getChild(childName.toName())
 
 
-
 /**
  * Update existing mutable node with another node. The rules are following:
  *  * value replaces anything
diff --git a/settings.gradle.kts b/settings.gradle.kts
index 7040baaf..0a7bdf3d 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -5,16 +5,13 @@ pluginManagement {
         gradlePluginPortal()
     }
 
-    val toolsVersion = "0.9.10"
-    val kotlinVersion = "1.5.10"
+    val toolsVersion = "0.10.0"
 
     plugins {
         id("ru.mipt.npm.gradle.project") version toolsVersion
         id("ru.mipt.npm.gradle.mpp") version toolsVersion
         id("ru.mipt.npm.gradle.jvm") version toolsVersion
         id("ru.mipt.npm.gradle.js") version toolsVersion
-        kotlin("jvm") version kotlinVersion
-        kotlin("js") version kotlinVersion
     }
 }