diff --git a/documentation/nt.rst b/documentation/nt.rst
index ced5075..129e816 100644
--- a/documentation/nt.rst
+++ b/documentation/nt.rst
@@ -24,6 +24,9 @@ time_t
 
 Commonly used sub-structure to represent a time
 
+.. doxygenstruct:: pvxs::nt::TimeStamp
+    :members:
+
 **"secondsPastEpoch"**
     Seconds since POSIX epoch of 1 Jan 1970 UTC.
     Note that the EPICS epoch is 631152000 seconds after the POSIX epoch.
@@ -37,6 +40,9 @@ Commonly used sub-structure to represent a time
 alarm_t
 -------
 
+.. doxygenstruct:: pvxs::nt::Alarm
+    :members:
+
 **"severity"**
     Enumeration of 0 - No Alarm, 1 - Minor, 2 - Major, 3 - Invalid.
 
diff --git a/src/nt.cpp b/src/nt.cpp
index 6f3c955..5f65b21 100644
--- a/src/nt.cpp
+++ b/src/nt.cpp
@@ -9,6 +9,30 @@
 namespace pvxs {
 namespace nt {
 
+TypeDef TimeStamp::build()
+{
+    using namespace pvxs::members;
+
+    TypeDef def(TypeCode::Struct, "time_t", {
+                    Int64("secondsPastEpoch"),
+                    Int32("nanoseconds"),
+                    Int32("userTag"),
+                });
+    return def;
+}
+
+TypeDef Alarm::build()
+{
+    using namespace pvxs::members;
+
+    TypeDef def(TypeCode::Struct, "alarm_t", {
+                    Int32("severity"),
+                    Int32("status"),
+                    String("message"),
+                });
+    return def;
+}
+
 TypeDef NTScalar::build() const
 {
     using namespace pvxs::members;
@@ -24,11 +48,7 @@ TypeDef NTScalar::build() const
                            Int32("status"),
                            String("message"),
                        }),
-                       Struct("timeStamp", "time_t", {
-                           Int64("secondsPastEpoch"),
-                           Int32("nanoseconds"),
-                           Int32("userTag"),
-                       }),
+                       TimeStamp{}.build().as("timeStamp"),
                    });
 
     const bool isnumeric = value.kind()==Kind::Integer || value.kind()==Kind::Real;
@@ -88,11 +108,7 @@ TypeDef NTNDArray::build() const
 {
     using namespace pvxs::members;
 
-    auto time_t = {
-        Int64("secondsPastEpoch"),
-        Int32("nanoseconds"),
-        Int32("userTag"),
-    };
+    auto time_t(TimeStamp{}.build());
     auto alarm_t = {
         Int32("severity"),
         Int32("status"),
@@ -120,9 +136,9 @@ TypeDef NTNDArray::build() const
                     Int64("compressedSize"),
                     Int64("uncompressedSize"),
                     Int32("uniqueId"),
-                    Struct("dataTimeStamp", "time_t", time_t),
+                    time_t.as("dataTimeStamp"),
                     Struct("alarm", "alarm_t", alarm_t),
-                    Struct("timeStamp", "time_t", time_t),
+                    time_t.as("timeStamp"),
                     StructA("dimension", "dimension_t", {
                         Int32("size"),
                         Int32("offset"),
@@ -136,7 +152,7 @@ TypeDef NTNDArray::build() const
                         StringA("tags"),
                         String("descriptor"),
                         Struct("alarm", "alarm_t", alarm_t),
-                        Struct("timeStamp", "time_t", time_t),
+                        time_t.as("timeStamp"),
                         Int32("sourceType"),
                         String("source"),
                     }),
diff --git a/src/pvxs/nt.h b/src/pvxs/nt.h
index ebe82e0..9acc74b 100644
--- a/src/pvxs/nt.h
+++ b/src/pvxs/nt.h
@@ -14,11 +14,38 @@ struct epicsTimeStamp; // epicsTime.h
 namespace pvxs {
 namespace nt {
 
+/** The time_t struct
+ *
+ * @code
+ * // equivalent
+ * struct time_t {
+ *     int64_t secondsPastEpoch;
+ *     int32_t nanoseconds;
+ *     int32_t userTag;
+ * };
+ * @endcode
+ */
 struct TimeStamp {
     PVXS_API
     TypeDef build();
 };
 
+/** The alarm_t struct
+ *
+ * @code
+ * // equivalent
+ * struct alarm_t {
+ *     int32_t severity;
+ *     int32_t status;
+ *     string message;
+ * };
+ * @endcode
+ */
+struct Alarm {
+    PVXS_API
+    TypeDef build();
+};
+
 /** A scalar, or array of scalars, and meta-data
  *
  * @code
diff --git a/test/testnt.cpp b/test/testnt.cpp
index 72420be..7393243 100644
--- a/test/testnt.cpp
+++ b/test/testnt.cpp
@@ -22,7 +22,7 @@ void testNTScalar()
     // plain, without display meta
     auto top = nt::NTScalar{TypeCode::Int32}.create();
 
-    testTrue(top.idStartsWith("epics:nt/NTScalar:"));
+    testTrue(top.idStartsWith("epics:nt/NTScalar:"))<<"\n"<<top;
 
     testEq(top["value"].type(), TypeCode::Int32);
     testEq(top["display.limitLow"].type(), TypeCode::Null);
@@ -52,7 +52,7 @@ void testNTNDArray()
 
     auto top = nt::NTNDArray{}.create();
 
-    testTrue(top.idStartsWith("epics:nt/NTNDArray:"));
+    testTrue(top.idStartsWith("epics:nt/NTNDArray:"))<<"\n"<<top;
 }
 
 void testNTURI()
@@ -68,7 +68,7 @@ void testNTURI()
 
     auto top = def.call(42, "hello");
 
-    testTrue(top.idStartsWith("epics:nt/NTURI:"));
+    testTrue(top.idStartsWith("epics:nt/NTURI:"))<<"\n"<<top;
     testEq(top["query.arg1"].as<uint32_t>(), 42u);
     testEq(top["query.arg2"].as<std::string>(), "hello");
 }