diff --git a/api/src/main/resources/schema/functions/functiondef.json b/api/src/main/resources/schema/functions/functiondef.json
index 4398aa50..ded52196 100644
--- a/api/src/main/resources/schema/functions/functiondef.json
+++ b/api/src/main/resources/schema/functions/functiondef.json
@@ -9,14 +9,15 @@
     },
     "operation": {
       "type": "string",
-      "description": "If type `rest`, combination of the function/service OpenAPI definition URI and the operationID of the operation that needs to be invoked, separated by a '#'. If type is `expression` defines the workflow expression.",
+      "description": "If type is `rest`, <path_to_openapi_definition>#<operation_id>. If type is `rpc`, <path_to_grpc_proto_file>#<service_name>#<service_method>. If type is `expression`, defines the workflow expression.",
       "minLength": 1
     },
     "type": {
       "type": "string",
-      "description": "Defines the function type. Is either `rest` or `expression`. Default is `rest`",
+      "description": "Defines the function type. Is either `rest`, `rpc` or `expression`. Default is `rest`",
       "enum": [
         "rest",
+        "rpc",
         "expression"
       ],
       "default": "rest"