diff --git a/include/maxscale/filter.h b/include/maxscale/filter.h
index d4f49cdc7..42effbed9 100644
--- a/include/maxscale/filter.h
+++ b/include/maxscale/filter.h
@@ -13,22 +13,16 @@
  */
 
 /**
- * @file filter.h -  The filter interface mechanisms
- *
- * Revision History
- *
- * Date         Who                     Description
- * 27/05/2014   Mark Riddoch            Initial implementation
- *
+ * @file include/maxscale/filter.h - The public filter interface
  */
 
 #include <maxscale/cdefs.h>
-#include <maxscale/config.h>
-#include <maxscale/routing.h>
-#include <maxscale/dcb.h>
-#include <maxscale/session.h>
-#include <maxscale/buffer.h>
 #include <stdint.h>
+#include <maxscale/buffer.h>
+#include <maxscale/config.h>
+#include <maxscale/dcb.h>
+#include <maxscale/routing.h>
+#include <maxscale/session.h>
 
 MXS_BEGIN_DECLS
 
@@ -56,19 +50,17 @@ typedef void *MXS_FILTER_SESSION;
  * The "module object" structure for a query router module
  *
  * The entry points are:
- *      createInstance          Called by the service to create a new
- *                              instance of the filter
- *      newSession              Called to create a new user session
- *                              within the filter
- *      closeSession            Called when a session is closed
- *      freeSession             Called when a session is freed
- *      setDownstream           Sets the downstream component of the
- *                              filter pipline
- *      routeQuery              Called on each query that requires
- *                              routing
- *      clientReply             Called for each reply packet
- *      diagnostics             Called to force the filter to print
- *                              diagnostic output
+ *      createInstance   Called by the service to create a new instance of the filter
+ *      newSession       Called to create a new user session within the filter
+ *      closeSession     Called when a session is closed
+ *      freeSession      Called when a session is freed
+ *      setDownstream    Sets the downstream component of the filter pipline
+ *      setUpstream      Sets the upstream component of the filter pipline
+ *      routeQuery       Called on each query that requires routing
+ *      clientReply      Called for each reply packet
+ *      diagnostics      Called for diagnostic output
+ *      getCapabilities  Called to obtain the capabilities of the filter
+ *      destroyInstance  Called for destroying a filter instance
  *
  * @endverbatim
  *
@@ -112,15 +104,8 @@ typedef struct filter_def
     struct filter_def *next;      /**< Next filter in the chain of all filters */
 } FILTER_DEF;
 
-FILTER_DEF *filter_alloc(const char *, const char *);
-void filter_free(FILTER_DEF *);
-bool filter_load(FILTER_DEF* filter);
 FILTER_DEF *filter_find(const char *);
-void filter_add_option(FILTER_DEF *, const char *);
-void filter_add_parameter(FILTER_DEF *, const char *, const char *);
-DOWNSTREAM *filter_apply(FILTER_DEF *, SESSION *, DOWNSTREAM *);
-UPSTREAM *filter_upstream(FILTER_DEF *, void *, UPSTREAM *);
-int filter_standard_parameter(const char *);
+
 void dprintAllFilters(DCB *);
 void dprintFilter(DCB *, const FILTER_DEF *);
 void dListFilters(DCB *);
diff --git a/server/core/maxscale/filter.h b/server/core/maxscale/filter.h
new file mode 100644
index 000000000..1fb0a7079
--- /dev/null
+++ b/server/core/maxscale/filter.h
@@ -0,0 +1,32 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+/**
+ * @file core/maxscale/filter.h - The private filter interface
+ */
+
+#include <maxscale/filter.h>
+
+MXS_BEGIN_DECLS
+
+void filter_add_option(FILTER_DEF *filter_def, const char *option);
+void filter_add_parameter(FILTER_DEF *filter_def, const char *name, const char *value);
+FILTER_DEF *filter_alloc(const char *name, const char *module_name);
+DOWNSTREAM *filter_apply(FILTER_DEF *filte_def, SESSION *session, DOWNSTREAM *downstream);
+void filter_free(FILTER_DEF *filter_def);
+bool filter_load(FILTER_DEF *filter_def);
+int filter_standard_parameter(const char *name);
+UPSTREAM *filter_upstream(FILTER_DEF *filter_def, void *fsession, UPSTREAM *upstream);
+
+MXS_END_DECLS
diff --git a/server/core/service.c b/server/core/service.c
index 0d8559b76..5eb558a05 100644
--- a/server/core/service.c
+++ b/server/core/service.c
@@ -38,6 +38,7 @@
  *
  * @endverbatim
  */
+#include <maxscale/service.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -47,26 +48,25 @@
 #include <sys/types.h>
 #include <math.h>
 #include <fcntl.h>
-#include <maxscale/session.h>
-#include <maxscale/protocol.h>
-#include <maxscale/listener.h>
-#include <maxscale/server.h>
-#include <maxscale/router.h>
-#include <maxscale/spinlock.h>
-#include <maxscale/modules.h>
-#include <maxscale/dcb.h>
-#include <maxscale/users.h>
-#include <maxscale/filter.h>
-#include <maxscale/poll.h>
-#include <maxscale/log_manager.h>
-#include <maxscale/housekeeper.h>
-#include <maxscale/resultset.h>
-#include <maxscale/gwdirs.h>
-#include <maxscale/version.h>
-#include <maxscale/queuemanager.h>
 #include <maxscale/alloc.h>
+#include <maxscale/dcb.h>
+#include <maxscale/gwdirs.h>
+#include <maxscale/housekeeper.h>
+#include <maxscale/listener.h>
+#include <maxscale/log_manager.h>
+#include <maxscale/modules.h>
+#include <maxscale/poll.h>
+#include <maxscale/protocol.h>
+#include <maxscale/queuemanager.h>
+#include <maxscale/resultset.h>
+#include <maxscale/router.h>
+#include <maxscale/server.h>
+#include <maxscale/session.h>
+#include <maxscale/spinlock.h>
+#include <maxscale/users.h>
 #include <maxscale/utils.h>
-
+#include <maxscale/version.h>
+#include "maxscale/filter.h"
 #include "maxscale/service.h"
 
 /** Base value for server weights */
diff --git a/server/core/session.c b/server/core/session.c
index b78326e3f..5ffc00a15 100644
--- a/server/core/session.c
+++ b/server/core/session.c
@@ -27,21 +27,22 @@
  *
  * @endverbatim
  */
+#include <maxscale/session.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
 #include <maxscale/alloc.h>
-#include <maxscale/session.h>
-#include <maxscale/service.h>
-#include <maxscale/router.h>
-#include <maxscale/dcb.h>
-#include <maxscale/spinlock.h>
 #include <maxscale/atomic.h>
-#include <maxscale/log_manager.h>
+#include <maxscale/dcb.h>
 #include <maxscale/housekeeper.h>
+#include <maxscale/log_manager.h>
 #include <maxscale/poll.h>
+#include <maxscale/router.h>
+#include <maxscale/service.h>
+#include <maxscale/spinlock.h>
+#include "maxscale/filter.h"
 
 /* A session with null values, used for initialization */
 static SESSION session_initialized = SESSION_INIT;
diff --git a/server/core/test/testfilter.c b/server/core/test/testfilter.c
index 2fb88b68a..ebdf84a6f 100644
--- a/server/core/test/testfilter.c
+++ b/server/core/test/testfilter.c
@@ -33,7 +33,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include <maxscale/filter.h>
+#include "../maxscale/filter.h"
 
 
 /**