diff --git a/behaverse/validators/nback.schema.json b/behaverse/validators/nback.schema.json
index 1feb724..800c99d 100644
--- a/behaverse/validators/nback.schema.json
+++ b/behaverse/validators/nback.schema.json
@@ -45,6 +45,79 @@
         "type": "string"
       }
     },
+    "Custom_NBack_TaskStart": {
+      "$comment": "NBack.TaskStart custom field",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "timeline": {"type": "string"},
+        "seed": {"type": "number"}
+      }
+    },
+    "Custom_NBack_BlockStart": {
+      "$comment": "NBack.BlockStart custom field. We need to seperate Instructions blocks from Game blocks",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "id": {"type": "number"},
+        "type": {"type": "string", "enum": [null, "Game", "Instructions"]}
+      }
+    },
+    "Custom_NBack_BlockEnd": {
+      "$comment": "NBack.BlockEnd custom field.",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "id": {"type": "number"},
+        "type": {"type": "string", "enum": ["Game", "Instructions"]},
+        "name": {"type": "string"},
+        "seed": {"type": "number"},
+        "accuracy": {"type": "number"},
+        "hitCount": {"type": "number", "minimum": 0},
+        "missCount": {"type": "number", "minimum": 0},
+        "falseAlarmCount": {"type": "number"},
+        "correctRejectionCount": {"type": "number"},
+        "timeOutCount": {"type": "number", "minimum": 0}
+
+      },
+      "required": ["id","type","name","seed","accuracy","hitCount","missCount", "falseAlaram", "correctRejectionCount", "timeOutCount"]
+    },
+    "Custom_NBack_TaskEnd": {
+      "$comment": "NBack.TaskEnd custom field.",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {}
+    },
+    "Custom_NBack_TrialEnd": {
+      "$comment": "NBack.TrialEnd custom field.",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {}
+    },
+    "Custom_NBack_TrialStart": {
+      "$comment": "NBack.TrialStart custom field.",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "id": {"type": "number"},
+        "seed": {"type": "number"}
+      }
+    },
+    "Custom_NBack_MatchingButtonClick": {
+      "$comment": "NBack.MatchingButtonClick custom field.",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "isMatch": {"type": "boolean"},
+        "pressDuration": {"type": "number"},
+        "pressTime": {"type": "string", "format": "date-time"},
+        "streamIndex": {"type": "number"},
+        "responseTime": {"type": ["number", "null"]},
+        "viewportPosition": { "$ref": "#/definitions/XY_Position" },
+        "worldPosition": { "$ref": "#/definitions/XY_Position" }
+      },
+      "required": ["worldPosition", "viewportPosition", "pressTime", "pressDuration", "isMatch", "streamIndex", "responseTime"]
+    },
     "Custom":{
       "type": "object",
       "$comment": "extract custom keys using this JQ query: '[.[] | .custom | keys | .[]] | unique | sort'",
@@ -75,67 +148,15 @@
         "viewportPosition": { "$ref": "#/definitions/XY_Position" },
         "worldPosition": { "$ref": "#/definitions/XY_Position" }
       },
-      "additionalProperties": true,
-      "anyOf": [
-        {
-          "if": {
-            "properties": {"types": {"enum": ["NBack.TaskStart"]}}
-          },
-          "then": {
-            "required": ["timeline", "seed"]
-          }
-        },
-        {
-          "if": {
-            "properties": {
-              "types": {"enum": ["NBack.BlockStart"]}
-            }
-          },
-          "then": {
-            "required": ["id", "type"]
-          }
-        },
-        {
-          "if": {
-            "properties": {"types": {"enum": ["NBack.BlockEnd"]}},
-            "$comment": "jq command to extract required parameters: [.[] | select(.types | .[] | contains(\"NBack.BlockEnd\")) | .custom | keys] | unique | .[][]"
-          },
-          "then": {
-            "required": ["id","type","name","seed","accuracy","hitCount","missCount", "falseAlaram", "correctRejectionCount", "timeOutCount"]
-          }
-        },
-        {
-          "if": {
-            "properties": {"types": {"enum": ["NBack.TaskEnd"]}}
-          },
-          "then": {
-            "required": []
-          }
-        },
-        {
-          "if": {
-            "properties": {"types": {"enum": ["NBack.TrialEnd"]}}
-          },
-          "then": {
-            "required": []
-          }
-        },
-        {
-          "if": {
-            "properties": {"types": {"enum": ["NBack.TrialStart"]}}
-          },
-          "then": {
-            "required": ["id", "seed"]
-          }
-        },
-        {
-          "if": {
-            "properties": {"types": {"enum": ["NBack.MatchingButtonClick"]}}
-          },
-          "then": {
-            "required": ["worldPosition", "viewportPosition", "pressTime", "pressDuration", "isMatch", "streamIndex", "responseTime"]
-          }
-        }
+      "additionalProperties": false,
+      "oneOf": [
+        { "$ref": "#/definitions/Custom_NBack_TaskStart"},
+        { "$ref": "#/definitions/Custom_NBack_BlockStart"},
+        { "$ref": "#/definitions/Custom_NBack_BlockEnd"},
+        { "$ref": "#/definitions/Custom_NBack_TaskEnd"},
+        { "$ref": "#/definitions/Custom_NBack_TrialEnd"},
+        { "$ref": "#/definitions/Custom_NBack_TrialStart"},
+        { "$ref": "#/definitions/Custom_NBack_MatchingButtonClick"}
       ]
     },
     "XY_Position": {