diff --git a/schemas/api/envelope.json b/schemas/api/envelope.json
index af6131d..5413745 100644
--- a/schemas/api/envelope.json
+++ b/schemas/api/envelope.json
@@ -11,7 +11,7 @@
             "description": "Unix timestamp showing when the data was generated, or the time the error was encountered"
         },
         "d": {
-            "description": "Payload data.  Type depends on request endpoint"
+            "description": "Payload data.  Type depends on request endpoint, typically an array of the response type"
         },
         "e": {
             "type": "object",
diff --git a/schemas/api/trains/TrainByHeadcode.json b/schemas/api/trains/TrainByHeadcode.json
new file mode 100644
index 0000000..c22886f
--- /dev/null
+++ b/schemas/api/trains/TrainByHeadcode.json
@@ -0,0 +1,41 @@
+{
+    "$schema": "https://json-schema.org/draft-07/schema#",
+    "title": "TrainByHeadcodeResponse",
+    "type": "object",
+    "required": ["r", "ot", "od", "dt", "o"],
+    "additionalProperties": false,
+    "properties": {
+        "r": {
+            "type": "string",
+            "name": "rid",
+            "description": "The RID of the service described"
+        },
+        "ot": {
+            "type": "string",
+            "name": "Origin TIPLOC",
+            "description": "The TIPLOC at which the service originates",
+            "minLength": 4,
+            "maxLength": 7
+        },
+        "od": {
+            "type": "string",
+            "name": "Origin Departure",
+            "format": "date-time",
+            "description": "The time that the service departs the originating location"
+        },
+        "dt": {
+            "type": "string",
+            "name": "Destination TIPLOC",
+            "description": "The TIPLOC at which the service terminates",
+            "minimum": 4,
+            "maximum": 7
+        },
+        "o": {
+            "type": "string",
+            "name": "Operator (TOC)",
+            "description": "The TOC operating the service",
+            "minLength": 2,
+            "maxLength": 2
+        }
+    }
+}
\ No newline at end of file