diff --git a/examples/roundrobinrouter.cpp b/examples/roundrobinrouter.cpp
index 73663b61d..c7a1c5fbe 100644
--- a/examples/roundrobinrouter.cpp
+++ b/examples/roundrobinrouter.cpp
@@ -572,7 +572,8 @@ static MXS_ROUTER_SESSION* newSession(MXS_ROUTER* instance, MXS_SESSION* session
 static void closeSession(MXS_ROUTER* instance, MXS_ROUTER_SESSION* session);
 static void freeSession(MXS_ROUTER* instance, MXS_ROUTER_SESSION* session);
 static int routeQuery(MXS_ROUTER* instance, MXS_ROUTER_SESSION* session, GWBUF* querybuf);
-static json_t* diagnostics(const MXS_ROUTER* instance);
+static void diagnostics(MXS_ROUTER* instance, DCB* dcb);
+static json_t* diagnostics_json(const MXS_ROUTER* instance);
 static void clientReply(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session,
                         GWBUF* resultbuf, DCB* backend_dcb);
 static void handleError(MXS_ROUTER* instance, MXS_ROUTER_SESSION* router_session,
@@ -600,6 +601,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
         freeSession,
         routeQuery,
         diagnostics,
+        diagnostics_json,
         clientReply,
         handleError,
         getCapabilities,
@@ -759,7 +761,24 @@ static int routeQuery(MXS_ROUTER* instance, MXS_ROUTER_SESSION* session, GWBUF*
  * @param   instance    The router instance
  * @param   dcb         The DCB for diagnostic output
  */
-static json_t* diagnostics(const MXS_ROUTER* instance)
+static void diagnostics(MXS_ROUTER* instance, DCB* dcb)
+{
+    RRRouter* router = static_cast<RRRouter*>(instance);
+    dcb_printf(dcb, "\t\tQueries routed successfully: %lu\n", router->m_routing_s);
+    dcb_printf(dcb, "\t\tFailed routing attempts:     %lu\n", router->m_routing_f);
+    dcb_printf(dcb, "\t\tClient replies routed:       %lu\n", router->m_routing_c);
+}
+
+/**
+ * @brief Diagnostics routine (API)
+ *
+ * Print router statistics to the DCB passed in. This is usually called by the
+ * MaxInfo or MaxAdmin modules.
+ *
+ * @param   instance    The router instance
+ * @param   dcb         The DCB for diagnostic output
+ */
+static json_t* diagnostics_json(const MXS_ROUTER* instance)
 {
     const RRRouter* router = static_cast<const RRRouter*>(instance);
     json_t* rval = json_object();
diff --git a/examples/testfilter.c b/examples/testfilter.c
index 7c97f6d35..8b2a2ab3d 100644
--- a/examples/testfilter.c
+++ b/examples/testfilter.c
@@ -35,7 +35,8 @@ static void closeSession(MXS_FILTER *instance, MXS_FILTER_SESSION *session);
 static void freeSession(MXS_FILTER *instance, MXS_FILTER_SESSION *session);
 static void setDownstream(MXS_FILTER *instance, MXS_FILTER_SESSION *fsession, MXS_DOWNSTREAM *downstream);
 static int routeQuery(MXS_FILTER *instance, MXS_FILTER_SESSION *fsession, GWBUF *queue);
-static json_t* diagnostic(const MXS_FILTER *instance, const MXS_FILTER_SESSION *fsession);
+static  void    diagnostic(MXS_FILTER *instance, MXS_FILTER_SESSION *fsession, DCB *dcb);
+static json_t* diagnostic_json(const MXS_FILTER *instance, const MXS_FILTER_SESSION *fsession);
 static uint64_t getCapabilities(MXS_FILTER* instance);
 static void destroyInstance(MXS_FILTER *instance);
 
@@ -78,6 +79,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
         routeQuery,
         NULL, // No clientReply
         diagnostic,
+        diagnostic_json,
         getCapabilities,
         destroyInstance,
     };
@@ -221,7 +223,32 @@ routeQuery(MXS_FILTER *instance, MXS_FILTER_SESSION *session, GWBUF *queue)
  * @param   fsession    Filter session, may be NULL
  * @param   dcb     The DCB for diagnostic output
  */
-static json_t* diagnostic(const MXS_FILTER *instance, const MXS_FILTER_SESSION *fsession)
+static  void
+diagnostic(MXS_FILTER *instance, MXS_FILTER_SESSION *fsession, DCB *dcb)
+{
+    TEST_INSTANCE   *my_instance = (TEST_INSTANCE *)instance;
+    TEST_SESSION    *my_session = (TEST_SESSION *)fsession;
+
+    if (my_session)
+        dcb_printf(dcb, "\t\tNo. of queries routed by filter: %d\n",
+                   my_session->count);
+    else
+        dcb_printf(dcb, "\t\tNo. of sessions created: %d\n",
+                   my_instance->sessions);
+}
+
+/**
+ * Diagnostics routine
+ *
+ * If fsession is NULL then print diagnostics on the filter
+ * instance as a whole, otherwise print diagnostics for the
+ * particular session.
+ *
+ * @param   instance    The filter instance
+ * @param   fsession    Filter session, may be NULL
+ * @param   dcb     The DCB for diagnostic output
+ */
+static json_t* diagnostic_json(const MXS_FILTER *instance, const MXS_FILTER_SESSION *fsession)
 {
     return NULL;
 }
diff --git a/examples/testroute.c b/examples/testroute.c
index 74572a933..1cbdfa469 100644
--- a/examples/testroute.c
+++ b/examples/testroute.c
@@ -21,7 +21,8 @@ static void closeSession(MXS_ROUTER *instance, MXS_ROUTER_SESSION *session);
 static void freeSession(MXS_ROUTER *instance, MXS_ROUTER_SESSION *session);
 static int routeQuery(MXS_ROUTER *instance, MXS_ROUTER_SESSION *session, GWBUF *queue);
 static void clientReply(MXS_ROUTER *instance, MXS_ROUTER_SESSION *session, GWBUF *queue, DCB*);
-static json_t* diagnostic(const MXS_ROUTER *instance);
+static void diagnostic(MXS_ROUTER *instance, DCB *dcb);
+static json_t* diagnostic_json(const MXS_ROUTER *instance);
 static uint64_t getCapabilities(MXS_ROUTER* instance);
 static void handleError(MXS_ROUTER *instance,
                         MXS_ROUTER_SESSION *router_session,
@@ -56,6 +57,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
         freeSession,
         routeQuery,
         diagnostic,
+        diagnostic_json,
         clientReply,
         handleError,
         getCapabilities,
@@ -145,7 +147,18 @@ void clientReply(MXS_ROUTER* instance, MXS_ROUTER_SESSION* session, GWBUF* queue
  * @param   instance    The router instance
  * @param   dcb     The DCB for diagnostic output
  */
-static json_t* diagnostic(const MXS_ROUTER *instance)
+static  void
+diagnostic(MXS_ROUTER *instance, DCB *dcb)
+{
+}
+
+/**
+ * Diagnostics routine
+ *
+ * @param   instance    The router instance
+ * @param   dcb     The DCB for diagnostic output
+ */
+static json_t* diagnostic_json(const MXS_ROUTER *instance)
 {
     return NULL;
 }
diff --git a/include/maxscale/authenticator.h b/include/maxscale/authenticator.h
index e77abb52c..4da3bada3 100644
--- a/include/maxscale/authenticator.h
+++ b/include/maxscale/authenticator.h
@@ -82,6 +82,7 @@ typedef struct mxs_authenticator
     void  (*free)(struct dcb *);
     void  (*destroy)(void *);
     int   (*loadusers)(struct servlistener *);
+    void  (*diagnostic)(struct dcb*, struct servlistener *);
 
     /**
      * @brief Return diagnostic information about the authenticator
@@ -95,7 +96,7 @@ typedef struct mxs_authenticator
      *
      * @see jansson.h
      */
-    json_t*  (*diagnostic)(const struct servlistener *listener);
+    json_t*  (*diagnostic_json)(const struct servlistener *listener);
 
     /** This entry point was added to avoid calling authenticator functions
      * directly when a COM_CHANGE_USER command is executed. */
diff --git a/include/maxscale/filter.h b/include/maxscale/filter.h
index 73b9e6b06..1952b1331 100644
--- a/include/maxscale/filter.h
+++ b/include/maxscale/filter.h
@@ -170,6 +170,15 @@ typedef struct mxs_filter_object
      */
     int32_t  (*clientReply)(MXS_FILTER *instance, MXS_FILTER_SESSION *fsession, GWBUF *queue);
 
+    /**
+     * @brief Called for diagnostic output
+     *
+     * @param instance Filter instance
+     * @param fsession Filter session, NULL if general information about the filter is queried
+     * @param dcb      DCB where the diagnostic information should be written
+     */
+    void     (*diagnostics)(MXS_FILTER *instance, MXS_FILTER_SESSION *fsession, DCB *dcb);
+
     /**
      * @brief Called for diagnostic output
      *
@@ -180,7 +189,7 @@ typedef struct mxs_filter_object
      *
      * @see jansson.h
      */
-    json_t* (*diagnostics)(const MXS_FILTER *instance, const MXS_FILTER_SESSION *fsession);
+    json_t* (*diagnostics_json)(const MXS_FILTER *instance, const MXS_FILTER_SESSION *fsession);
 
     /**
      * @brief Called to obtain the capabilities of the filter
diff --git a/include/maxscale/filter.hh b/include/maxscale/filter.hh
index 69b2cd414..d66051b0a 100644
--- a/include/maxscale/filter.hh
+++ b/include/maxscale/filter.hh
@@ -144,8 +144,15 @@ public:
 
     /**
      * Called for obtaining diagnostics about the filter session.
+     *
+     * @param pDcb  The dcb where the diagnostics should be written.
      */
-    json_t* diagnostics() const;
+    void diagnostics(DCB *pDcb);
+
+    /**
+     * Called for obtaining diagnostics about the filter session.
+     */
+    json_t* diagnostics_json() const;
 
 protected:
     FilterSession(MXS_SESSION* pSession);
@@ -272,7 +279,23 @@ public:
         return rv;
     }
 
-    static json_t* diagnostics(const MXS_FILTER* pInstance, const MXS_FILTER_SESSION* pData)
+    static void diagnostics(MXS_FILTER* pInstance, MXS_FILTER_SESSION* pData, DCB* pDcb)
+    {
+        if (pData)
+        {
+            FilterSessionType* pFilterSession = static_cast<FilterSessionType*>(pData);
+
+            MXS_EXCEPTION_GUARD(pFilterSession->diagnostics(pDcb));
+        }
+        else
+        {
+            FilterType* pFilter = static_cast<FilterType*>(pInstance);
+
+            MXS_EXCEPTION_GUARD(pFilter->diagnostics(pDcb));
+        }
+    }
+
+    static json_t* diagnostics_json(const MXS_FILTER* pInstance, const MXS_FILTER_SESSION* pData)
     {
         json_t* rval = NULL;
 
@@ -280,13 +303,13 @@ public:
         {
             const FilterSessionType* pFilterSession = static_cast<const FilterSessionType*>(pData);
 
-            MXS_EXCEPTION_GUARD(rval = pFilterSession->diagnostics());
+            MXS_EXCEPTION_GUARD(rval = pFilterSession->diagnostics_json());
         }
         else
         {
             const FilterType* pFilter = static_cast<const FilterType*>(pInstance);
 
-            MXS_EXCEPTION_GUARD(rval = pFilter->diagnostics());
+            MXS_EXCEPTION_GUARD(rval = pFilter->diagnostics_json());
         }
 
         return rval;
@@ -326,6 +349,7 @@ MXS_FILTER_OBJECT Filter<FilterType, FilterSessionType>::s_object =
     &Filter<FilterType, FilterSessionType>::routeQuery,
     &Filter<FilterType, FilterSessionType>::clientReply,
     &Filter<FilterType, FilterSessionType>::diagnostics,
+    &Filter<FilterType, FilterSessionType>::diagnostics_json,
     &Filter<FilterType, FilterSessionType>::getCapabilities,
     &Filter<FilterType, FilterSessionType>::destroyInstance,
 };
diff --git a/include/maxscale/monitor.h b/include/maxscale/monitor.h
index 3c5433ab7..44e100fb4 100644
--- a/include/maxscale/monitor.h
+++ b/include/maxscale/monitor.h
@@ -78,6 +78,7 @@ typedef struct mxs_monitor_object
      * @param monitor The monitor object
      */
     void (*stopMonitor)(MXS_MONITOR *monitor);
+    void (*diagnostics)(DCB *, const MXS_MONITOR *);
 
     /**
      * @brief Return diagnostic information about the monitor
@@ -86,7 +87,7 @@ typedef struct mxs_monitor_object
      *
      * @see jansson.h
      */
-    json_t* (*diagnostics)(const MXS_MONITOR *monitor);
+    json_t* (*diagnostics_json)(const MXS_MONITOR *monitor);
 } MXS_MONITOR_OBJECT;
 
 /**
diff --git a/include/maxscale/router.h b/include/maxscale/router.h
index e3af7c6df..cc6aa08cf 100644
--- a/include/maxscale/router.h
+++ b/include/maxscale/router.h
@@ -145,6 +145,15 @@ typedef struct mxs_router_object
      */
     int32_t  (*routeQuery)(MXS_ROUTER *instance, MXS_ROUTER_SESSION *router_session, GWBUF *queue);
 
+
+    /**
+     * @brief Called for diagnostic output
+     *
+     * @param instance Router instance
+     * @param dcb      DCB where the diagnostic information should be written
+     */
+    void     (*diagnostics)(MXS_ROUTER *instance, DCB *dcb);
+
     /**
      * @brief Called for diagnostic output
      *
@@ -154,7 +163,7 @@ typedef struct mxs_router_object
      *
      * @see jansson.h
      */
-    json_t*  (*diagnostics)(const MXS_ROUTER *instance);
+    json_t*  (*diagnostics_json)(const MXS_ROUTER *instance);
 
     /**
      * @brief Called for each reply packet
diff --git a/include/maxscale/router.hh b/include/maxscale/router.hh
index ec51e7275..b3800ba50 100644
--- a/include/maxscale/router.hh
+++ b/include/maxscale/router.hh
@@ -173,13 +173,20 @@ public:
         return rv;
     }
 
-    static json_t* diagnostics(const MXS_ROUTER* pInstance)
+    static void diagnostics(MXS_ROUTER* pInstance, DCB* pDcb)
+    {
+        RouterType* pRouter = static_cast<RouterType*>(pInstance);
+
+        MXS_EXCEPTION_GUARD(pRouter->diagnostics(pDcb));
+    }
+
+    static json_t* diagnostics_json(const MXS_ROUTER* pInstance)
     {
         const RouterType* pRouter = static_cast<const RouterType*>(pInstance);
 
         json_t* rval = NULL;
 
-        MXS_EXCEPTION_GUARD(rval = pRouter->diagnostics());
+        MXS_EXCEPTION_GUARD(rval = pRouter->diagnostics_json());
 
         return rval;
     }
@@ -242,6 +249,7 @@ MXS_ROUTER_OBJECT Router<RouterType, RouterSessionType>::s_object =
     &Router<RouterType, RouterSessionType>::freeSession,
     &Router<RouterType, RouterSessionType>::routeQuery,
     &Router<RouterType, RouterSessionType>::diagnostics,
+    &Router<RouterType, RouterSessionType>::diagnostics_json,
     &Router<RouterType, RouterSessionType>::clientReply,
     &Router<RouterType, RouterSessionType>::handleError,
     &Router<RouterType, RouterSessionType>::getCapabilities,
diff --git a/include/maxscale/users.h b/include/maxscale/users.h
index ad8384596..ab4accc59 100644
--- a/include/maxscale/users.h
+++ b/include/maxscale/users.h
@@ -115,9 +115,17 @@ int users_default_loadusers(SERV_LISTENER *port);
 /**
  * @brief Default authenticator diagnostic function
  *
+ * @param dcb DCB where data is printed
  * @param port Port whose data is to be printed
  */
-json_t* users_default_diagnostic(const SERV_LISTENER *port);
+void users_default_diagnostic(DCB *dcb, SERV_LISTENER *port);
+
+/**
+ * @brief Default authenticator diagnostic function
+ *
+ * @param port Port whose data is to be printed
+ */
+json_t* users_default_diagnostic_json(const SERV_LISTENER *port);
 
 /**
  * Print details of the users storage mechanism
diff --git a/server/core/filter.cc b/server/core/filter.cc
index d46fc007e..71db12b11 100644
--- a/server/core/filter.cc
+++ b/server/core/filter.cc
@@ -212,12 +212,7 @@ dprintAllFilters(DCB *dcb)
         }
         if (ptr->obj && ptr->filter)
         {
-            json_t* json = ptr->obj->diagnostics(ptr->filter, NULL);
-
-            if (json)
-            {
-                json_decref(json);
-            }
+           ptr->obj->diagnostics(ptr->filter, NULL, dcb);
         }
         else
         {
@@ -252,12 +247,7 @@ dprintFilter(DCB *dcb, const MXS_FILTER_DEF *filter)
     }
     if (filter->obj && filter->filter)
     {
-        json_t* json = filter->obj->diagnostics(filter->filter, NULL);
-
-        if (json)
-        {
-            json_decref(json);
-        }
+        filter->obj->diagnostics(filter->filter, NULL, dcb);
     }
 }
 
@@ -503,7 +493,7 @@ json_t* filter_to_json(const MXS_FILTER_DEF* filter, const char* host)
 
     if (filter->obj && filter->filter)
     {
-        json_t* diag = filter->obj->diagnostics(filter->filter, NULL);
+        json_t* diag = filter->obj->diagnostics_json(filter->filter, NULL);
 
         if (diag)
         {
@@ -596,7 +586,11 @@ int FilterSession::clientReply(GWBUF* pPacket)
     return m_up.clientReply(pPacket);
 }
 
-json_t* FilterSession::diagnostics() const
+void FilterSession::diagnostics(DCB *pDcb)
+{
+}
+
+json_t* FilterSession::diagnostics_json() const
 {
     return NULL;
 }
diff --git a/server/core/monitor.cc b/server/core/monitor.cc
index ce93fa519..d3e6e9980 100644
--- a/server/core/monitor.cc
+++ b/server/core/monitor.cc
@@ -477,12 +477,7 @@ monitorShow(DCB *dcb, MXS_MONITOR *monitor)
     {
         if (monitor->module->diagnostics)
         {
-            json_t* json = monitor->module->diagnostics(monitor);
-
-            if (json)
-            {
-                json_decref(json);
-            }
+            monitor->module->diagnostics(dcb, monitor);
         }
         else
         {
@@ -1550,7 +1545,7 @@ json_t* monitor_to_json(const MXS_MONITOR* monitor, const char* host)
 
     if (monitor->handle && monitor->module->diagnostics)
     {
-        json_t* diag = monitor->module->diagnostics(monitor);
+        json_t* diag = monitor->module->diagnostics_json(monitor);
 
         if (diag)
         {
diff --git a/server/core/service.cc b/server/core/service.cc
index f6bd50c6b..9c69022be 100644
--- a/server/core/service.cc
+++ b/server/core/service.cc
@@ -1415,12 +1415,7 @@ void dprintService(DCB *dcb, SERVICE *service)
     }
     if (service->router && service->router_instance)
     {
-        json_t* json = service->router->diagnostics(service->router_instance);
-
-        if (json)
-        {
-            json_decref(json);
-        }
+        service->router->diagnostics(service->router_instance, dcb);
     }
     dcb_printf(dcb, "\tStarted:                             %s",
                asctime_r(localtime_r(&service->stats.started, &result), timebuf));
@@ -2298,12 +2293,7 @@ void service_print_users(DCB *dcb, const SERVICE *service)
     {
         if (port->listener && port->listener->authfunc.diagnostic)
         {
-            json_t* json = port->listener->authfunc.diagnostic(port);
-
-            if (json)
-            {
-                json_decref(json);
-            }
+            port->listener->authfunc.diagnostic(dcb, port);
         }
     }
 }
@@ -2368,7 +2358,7 @@ json_t* service_to_json(const SERVICE* service, const char* host)
 
     if (service->router && service->router_instance)
     {
-        json_t* diag = service->router->diagnostics(service->router_instance);
+        json_t* diag = service->router->diagnostics_json(service->router_instance);
 
         if (diag)
         {
diff --git a/server/core/session.cc b/server/core/session.cc
index b05e02ece..18b42d014 100644
--- a/server/core/session.cc
+++ b/server/core/session.cc
@@ -533,13 +533,9 @@ dprintSession(DCB *dcb, MXS_SESSION *print_session)
         {
             dcb_printf(dcb, "\tFilter: %s\n",
                        print_session->filters[i].filter->name);
-            json_t* json = print_session->filters[i].filter->obj->diagnostics(print_session->filters[i].instance,
-                                                               print_session->filters[i].session);
-
-            if (json)
-            {
-                json_decref(json);
-            }
+            print_session->filters[i].filter->obj->diagnostics(print_session->filters[i].instance,
+                                                               print_session->filters[i].session,
+                                                               dcb);
         }
     }
 }
diff --git a/server/core/users.cc b/server/core/users.cc
index b66a22102..6ac253c21 100644
--- a/server/core/users.cc
+++ b/server/core/users.cc
@@ -109,7 +109,35 @@ void usersPrint(const USERS *users)
     hashtable_stats(users->data);
 }
 
-json_t* users_default_diagnostic(const SERV_LISTENER *port)
+void users_default_diagnostic(DCB *dcb, SERV_LISTENER *port)
+{
+    if (port->users && port->users->data)
+    {
+        HASHITERATOR *iter = hashtable_iterator(port->users->data);
+
+        if (iter)
+        {
+            dcb_printf(dcb, "User names: ");
+            const char *sep = "";
+            void *user;
+
+            while ((user = hashtable_next(iter)) != NULL)
+            {
+                dcb_printf(dcb, "%s%s", sep, (char *)user);
+                sep = ", ";
+            }
+
+            dcb_printf(dcb, "\n");
+            hashtable_iterator_free(iter);
+        }
+    }
+    else
+    {
+        dcb_printf(dcb, "Users table is empty\n");
+    }
+}
+
+json_t* users_default_diagnostic_json(const SERV_LISTENER *port)
 {
     json_t* rval = json_array();