diff --git a/build.gradle.kts b/build.gradle.kts
index 812863f..503fe1c 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -30,6 +30,8 @@ dependencies {
     implementation("de.bixilon:kutil:1.23.2")
     implementation("de.bixilon:mbf-kotlin:1.0.2")
 
+    implementation("it.unimi.dsi", "fastutil-core", "8.5.12")
+
     testImplementation(kotlin("test"))
 }
 
diff --git a/src/main/kotlin/de.bixilon.minosoft.meta.transpiler/MinosoftMetaTranspiler.kt b/src/main/kotlin/de.bixilon.minosoft.meta.transpiler/MinosoftMetaTranspiler.kt
index 97d3779..4cdc47e 100644
--- a/src/main/kotlin/de.bixilon.minosoft.meta.transpiler/MinosoftMetaTranspiler.kt
+++ b/src/main/kotlin/de.bixilon.minosoft.meta.transpiler/MinosoftMetaTranspiler.kt
@@ -13,7 +13,6 @@ import de.bixilon.mbf.MBFBinaryWriter
 import de.bixilon.mbf.MBFCompressionTypes
 import de.bixilon.mbf.MBFData
 import de.bixilon.mbf.MBFDataInfo
-import de.bixilon.minosoft.meta.transpiler.processors.GenericProcessor
 import de.bixilon.minosoft.meta.transpiler.processors.Processors
 import java.io.*
 import java.util.*
@@ -45,7 +44,8 @@ object MinosoftMetaTranspiler {
 
         if (error.isNotEmpty()) {
             for (error in error) {
-                System.err.println("Error in version ${error.version} in type ${error.type}: ${error.cause}")
+                System.err.println("Error in version ${error.version} in type ${error.type}:")
+                error.cause!!.printStackTrace()
             }
             exitProcess(1)
         }
@@ -93,12 +93,12 @@ object MinosoftMetaTranspiler {
     }
 
     private fun readFile(stream: InputStream, version: String, type: String, output: File) {
-        val processor = Processors.types[type] ?: GenericProcessor
+        val processor = Processors.types[type]?.build()
         try {
             println("Validating $type ($version)")
             total.incrementAndGet()
             val json: JsonObject = Jackson.MAPPER.readValue(stream)
-            processor.validate(json)
+            processor?.validate(json)
             val hash = storeMbf(json, output)
             val entry = MetaVersionEntry(version, hash)
             mbf.synchronizedGetOrPut(type) { Collections.synchronizedList(mutableListOf()) } += entry
diff --git a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/BlockProcessor.kt b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/BlockProcessor.kt
new file mode 100644
index 0000000..9c1bdd5
--- /dev/null
+++ b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/BlockProcessor.kt
@@ -0,0 +1,51 @@
+package de.bixilon.minosoft.meta.transpiler.processors
+
+import de.bixilon.kutil.cast.CastUtil.unsafeCast
+import de.bixilon.kutil.json.JsonObject
+import de.bixilon.kutil.primitive.IntUtil.toInt
+import it.unimi.dsi.fastutil.ints.IntOpenHashSet
+
+class BlockProcessor : Processor {
+    private val ids = IntOpenHashSet()
+
+    private fun validateId(identifier: String, data: JsonObject): Int {
+        val id = data["id"]!!.toInt()
+        if (id < 1) throw IllegalArgumentException("Id < 1: $id for item $identifier")
+        if (id > 0xFF) throw IllegalArgumentException("Id > 0xFF: $id for item $identifier")
+        return id
+    }
+
+    private fun validateMeta(identifier: String, data: JsonObject): Int {
+        val meta = data["meta"]?.toInt() ?: return 0
+        if (meta < 0) throw IllegalArgumentException("Meta < 0: $meta for item $identifier")
+        if (meta > 0x0F) throw IllegalArgumentException("Meta > 0x0F: $meta for item $identifier")
+        return meta
+    }
+
+    override fun validateEntry(identifier: String, data: JsonObject) {
+        val states = data["states"]
+        if (states != null) {
+            return validateStates(identifier, states.unsafeCast())
+        }
+        validateIdAndMeta(identifier, data)
+    }
+
+    private fun validateStates(identifier: String, states: List<JsonObject>) {
+        for (entry in states) {
+            validateIdAndMeta(identifier, entry)
+        }
+    }
+
+    private fun validateIdAndMeta(identifier: String, data: JsonObject) {
+        val id = validateId(identifier, data)
+        val meta = validateMeta(identifier, data)
+        val combined = id shl 4 or meta
+        if (!ids.add(combined)) {
+            throw IllegalStateException("Id duplicated $id (meta=$meta)")
+        }
+    }
+
+    companion object : ProcessorBuilder {
+        override fun build() = BlockProcessor()
+    }
+}
diff --git a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/GenericProcessor.kt b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/GenericProcessor.kt
deleted file mode 100644
index 4dae100..0000000
--- a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/GenericProcessor.kt
+++ /dev/null
@@ -1,7 +0,0 @@
-package de.bixilon.minosoft.meta.transpiler.processors
-
-import de.bixilon.kutil.json.JsonObject
-
-object GenericProcessor : Processor {
-    override fun validate(data: JsonObject) = Unit
-}
diff --git a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/ItemProcessor.kt b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/ItemProcessor.kt
new file mode 100644
index 0000000..8488a9f
--- /dev/null
+++ b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/ItemProcessor.kt
@@ -0,0 +1,38 @@
+package de.bixilon.minosoft.meta.transpiler.processors
+
+import de.bixilon.kutil.json.JsonObject
+import de.bixilon.kutil.primitive.IntUtil.toInt
+import it.unimi.dsi.fastutil.ints.IntOpenHashSet
+
+class ItemProcessor : Processor {
+    private val ids = IntOpenHashSet()
+
+    private fun validateId(identifier: String, data: JsonObject): Int {
+        val id = data["id"]!!.toInt()
+        if (id < 1) throw IllegalArgumentException("Id < 1: $id for item $identifier")
+        if (id > 0xFFFF) throw IllegalArgumentException("Id > 0xFFFF: $id for item $identifier")
+
+        return id
+    }
+
+    private fun validateMeta(identifier: String, data: JsonObject): Int {
+        val meta = data["meta"]?.toInt() ?: return 0
+        if (meta < 0) throw IllegalArgumentException("Meta < 0: $meta for item $identifier")
+        if (meta > 0xFFFF) throw IllegalArgumentException("Meta > 0xFFFF: $meta for item $identifier")
+
+        return meta
+    }
+
+    override fun validateEntry(identifier: String, data: JsonObject) {
+        val id = validateId(identifier, data)
+        val meta = validateMeta(identifier, data)
+        val combined = id shl 16 or meta
+        if (!this.ids.add(combined)) {
+            throw IllegalStateException("Id duplicated: $id (meta=$meta)")
+        }
+    }
+
+    companion object : ProcessorBuilder {
+        override fun build() = ItemProcessor()
+    }
+}
diff --git a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processor.kt b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processor.kt
index f494054..4ef1309 100644
--- a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processor.kt
+++ b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processor.kt
@@ -1,7 +1,15 @@
 package de.bixilon.minosoft.meta.transpiler.processors
 
+import de.bixilon.kutil.cast.CastUtil.unsafeCast
 import de.bixilon.kutil.json.JsonObject
 
 interface Processor {
-    fun validate(data: JsonObject)
+
+    fun validate(data: JsonObject) {
+        for ((key, value) in data) {
+            validateEntry(key.removePrefix("minecraft:"), value.unsafeCast())
+        }
+    }
+
+    fun validateEntry(identifier: String, data: JsonObject)
 }
diff --git a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/ProcessorBuilder.kt b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/ProcessorBuilder.kt
new file mode 100644
index 0000000..2d00935
--- /dev/null
+++ b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/ProcessorBuilder.kt
@@ -0,0 +1,6 @@
+package de.bixilon.minosoft.meta.transpiler.processors
+
+fun interface ProcessorBuilder {
+
+    fun build(): Processor
+}
diff --git a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processors.kt b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processors.kt
index 4ad4497..277fcc1 100644
--- a/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processors.kt
+++ b/src/main/kotlin/de/bixilon/minosoft/meta/transpiler/processors/Processors.kt
@@ -1,7 +1,8 @@
 package de.bixilon.minosoft.meta.transpiler.processors
 
 object Processors {
-    val types: MutableMap<String, Processor> = mutableMapOf(
-
+    val types: MutableMap<String, ProcessorBuilder> = mutableMapOf(
+        "items" to ItemProcessor,
+        "blocks" to BlockProcessor,
     )
 }