diff --git a/docs/source/interface.rst b/docs/source/interface.rst
index 74da5a897666f800948ed2863b44cc0f98ce9923..0ec7d3910c1fe7a70d769f67324dac3bb2eb8b98 100644
--- a/docs/source/interface.rst
+++ b/docs/source/interface.rst
@@ -32,10 +32,16 @@ If the voucher is not known then the response is **NOT FOUND**.
 For any voucher which has previously been submitted,
 the response is **OK** with an ``application/json`` content-type response body like::
 
-  {"value": <string>}
+  {"value": <string>, "created": <iso8601 timestamp>, "redeemed": bool, "version": 1}
 
 The ``value`` property merely indicates the voucher which was requested.
-Further properties will be added to this response in the near future.
+The ``created`` property indicates when the voucher was first added to the node.
+The ``redeemed`` property indicates whether or not the voucher has successfully been redeemed with a payment server yet.
+
+The ``version`` property indicates the semantic version of the data being returned.
+When properties are removed or the meaning of a property is changed,
+the value of the ``version`` property will be incremented.
+The addition of new properties is **not** accompanied by a bumped version number.
 
 ``GET /storage-plugins/privatestorageio-zkapauthz-v1/voucher``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~