diff --git a/api-ref/source/v2/parameters.yaml b/api-ref/source/v2/parameters.yaml
index 465dfa60d81..11e8c374f49 100644
--- a/api-ref/source/v2/parameters.yaml
+++ b/api-ref/source/v2/parameters.yaml
@@ -662,7 +662,7 @@ has_dependent_backups:
 host:
   description: |
     The OpenStack Block Storage host where the
-    existing volume resides.
+    existing volume resides. Host format is ``host@backend``.
   in: body
   required: true
   type: string
@@ -1270,6 +1270,7 @@ os-unset_image_metadata:
 os-vol-host-attr:host:
   description: |
     Current back-end of the volume.
+    Host format is ``host@backend#pool``.
   in: body
   required: true
   type: string
diff --git a/api-ref/source/v3/parameters.yaml b/api-ref/source/v3/parameters.yaml
index 6d94c1edbfa..f6e7e288160 100644
--- a/api-ref/source/v3/parameters.yaml
+++ b/api-ref/source/v3/parameters.yaml
@@ -1243,7 +1243,7 @@ has_dependent_backups:
 host:
   description: |
     The OpenStack Block Storage host where the
-    existing volume resides.
+    existing volume resides. Host format is ``host@backend``.
   in: body
   required: true
   type: object
@@ -1986,6 +1986,7 @@ os-unset_image_metadata:
 os-vol-host-attr:host:
   description: |
     Current back-end of the volume.
+    Host format is ``host@backend#pool``.
   in: body
   required: true
   type: string