diff --git a/dataforge-io/src/commonMain/kotlin/hep/dataforge/io/TaggedEnvelopeFormat.kt b/dataforge-io/src/commonMain/kotlin/hep/dataforge/io/TaggedEnvelopeFormat.kt
index c51cb36d..97a23fb9 100644
--- a/dataforge-io/src/commonMain/kotlin/hep/dataforge/io/TaggedEnvelopeFormat.kt
+++ b/dataforge-io/src/commonMain/kotlin/hep/dataforge/io/TaggedEnvelopeFormat.kt
@@ -13,7 +13,8 @@ import kotlinx.io.core.*
 @ExperimentalUnsignedTypes
 class TaggedEnvelopeFormat(
     val io: IOPlugin,
-    private val metaFormatKey: Short
+    private val metaFormatKey: Short,
+    val version: VERSION = TaggedEnvelopeFormat.VERSION.DF02
 ) : EnvelopeFormat {
 
     private val metaFormat = io.metaFormat(metaFormatKey)
@@ -22,10 +23,17 @@ class TaggedEnvelopeFormat(
 
     private fun Tag.toBytes(): ByteReadPacket = buildPacket(24) {
         writeText(START_SEQUENCE)
-        writeText(VERSION)
+        writeText(version.name)
         writeShort(metaFormatKey)
         writeUInt(metaSize)
-        writeULong(dataSize)
+        when (version) {
+            TaggedEnvelopeFormat.VERSION.DF02 -> {
+                writeUInt(dataSize.toUInt())
+            }
+            TaggedEnvelopeFormat.VERSION.DF03 -> {
+                writeULong(dataSize)
+            }
+        }
         writeText(END_SEQUENCE)
     }
 
@@ -46,7 +54,7 @@ class TaggedEnvelopeFormat(
      * @param formats a collection of meta formats to resolve
      */
     override fun Input.readObject(): Envelope {
-        val tag = readTag()
+        val tag = readTag(version)
 
         val metaFormat = io.metaFormat(tag.metaFormatKey)
             ?: error("Meta format with key ${tag.metaFormatKey} not found")
@@ -59,7 +67,7 @@ class TaggedEnvelopeFormat(
     }
 
     override fun Input.readPartial(): PartialEnvelope {
-        val tag = readTag()
+        val tag = readTag(version)
 
         val metaFormat = io.metaFormat(tag.metaFormatKey)
             ?: error("Meta format with key ${tag.metaFormatKey} not found")
@@ -67,7 +75,7 @@ class TaggedEnvelopeFormat(
         val metaPacket = ByteReadPacket(readBytes(tag.metaSize.toInt()))
         val meta = metaFormat.run { metaPacket.readObject() }
 
-        return PartialEnvelope(meta, TAG_SIZE + tag.metaSize, tag.dataSize)
+        return PartialEnvelope(meta, version.tagSize + tag.metaSize, tag.dataSize)
     }
 
     private data class Tag(
@@ -76,13 +84,16 @@ class TaggedEnvelopeFormat(
         val dataSize: ULong
     )
 
+    enum class VERSION(val tagSize: UInt) {
+        DF02(20u),
+        DF03(24u)
+    }
+
     companion object : EnvelopeFormatFactory {
-        const val VERSION = "DF03"
         private const val START_SEQUENCE = "#~"
         private const val END_SEQUENCE = "~#\r\n"
-        private const val TAG_SIZE = 24u
 
-        override val name: Name = super.name + VERSION
+        override val name: Name = super.name + "tagged"
 
         override fun invoke(meta: Meta, context: Context): EnvelopeFormat {
             val io = context.io
@@ -94,14 +105,17 @@ class TaggedEnvelopeFormat(
             return TaggedEnvelopeFormat(io, metaFormatFactory.key)
         }
 
-        private fun Input.readTag(): Tag {
+        private fun Input.readTag(version: VERSION): Tag {
             val start = readTextExactBytes(2, charset = Charsets.ISO_8859_1)
             if (start != START_SEQUENCE) error("The input is not an envelope")
-            val version = readTextExactBytes(4, charset = Charsets.ISO_8859_1)
-            if (version != VERSION) error("Wrong version of DataForge: expected $VERSION but found $version")
+            val versionString = readTextExactBytes(4, charset = Charsets.ISO_8859_1)
+            if (version.name != versionString) error("Wrong version of DataForge: expected $version but found $versionString")
             val metaFormatKey = readShort()
             val metaLength = readUInt()
-            val dataLength = readULong()
+            val dataLength: ULong = when (version) {
+                VERSION.DF02 -> readUInt().toULong()
+                VERSION.DF03 -> readULong()
+            }
             val end = readTextExactBytes(4, charset = Charsets.ISO_8859_1)
             if (end != END_SEQUENCE) error("The input is not an envelope")
             return Tag(metaFormatKey, metaLength, dataLength)
@@ -109,14 +123,18 @@ class TaggedEnvelopeFormat(
 
         override fun peekFormat(io: IOPlugin, input: Input): EnvelopeFormat? {
             return try {
-                val tag = input.readTag()
-                TaggedEnvelopeFormat(io, tag.metaFormatKey)
+                val header = input.readTextExactBytes(6)
+                when(header.substring(2..5)){
+                    VERSION.DF02.name-> TaggedEnvelopeFormat(io, JsonMetaFormat.key,VERSION.DF02)
+                    VERSION.DF03.name-> TaggedEnvelopeFormat(io, JsonMetaFormat.key,VERSION.DF03)
+                    else -> null
+                }
             } catch (ex: Exception) {
                 null
             }
         }
 
-        val default by lazy {  invoke()}
+        val default by lazy { invoke() }
     }
 
 }
\ No newline at end of file