diff --git a/src/extensions/authbasic.ml b/src/extensions/authbasic.ml
index ea2670dbd..1c8e005d7 100644
--- a/src/extensions/authbasic.ml
+++ b/src/extensions/authbasic.ml
@@ -111,4 +111,7 @@ let () =
     ()
 
 (** Instruction for static linking without config file: *)
-let run ~realm ~auth () _ _ _ = gen ~realm ~auth
+let instruction ~realm ~auth () _ _ _ = gen ~realm ~auth
+
+let run ?site ~realm ~auth () =
+  Ocsigen_server.Site.register ?site (instruction ~realm ~auth ())
diff --git a/src/extensions/authbasic.mli b/src/extensions/authbasic.mli
index 134d0250d..118fb5970 100644
--- a/src/extensions/authbasic.mli
+++ b/src/extensions/authbasic.mli
@@ -59,7 +59,12 @@ val register_basic_authentication_method : (Xml.xml -> auth) -> unit
     from the point of view of plugin developers and is totally
     transparent to the plugin. *)
 
-val run : realm:string -> auth:auth -> unit -> Ocsigen_server.Site.instruction
+val run :
+   ?site:Ocsigen_server.Site.t
+  -> realm:string
+  -> auth:auth
+  -> unit
+  -> unit
 (** [run ~realm ~auth ()] makes it possible to use this extension without 
     configuration file.  *)
 
diff --git a/src/extensions/cors.ml b/src/extensions/cors.ml
index 273f2a059..2de2e5d28 100644
--- a/src/extensions/cors.ml
+++ b/src/extensions/cors.ml
@@ -156,7 +156,11 @@ let () =
     ~fun_site:(fun _ _ _ -> parse_config)
     ()
 
-let run ?credentials ?max_age ?exposed_headers ?methods () _ _ _ =
+let instruction ?credentials ?max_age ?exposed_headers ?methods () _ _ _ =
   let credentials = Ocsigen_lib.Option.get' false credentials in
   let exposed_headers = Ocsigen_lib.Option.get' [] exposed_headers in
   main {credentials; methods; max_age; exposed_headers}
+
+let run ?site ?credentials ?max_age ?exposed_headers ?methods () =
+  Ocsigen_server.Site.register ?site
+    (instruction ?credentials ?max_age ?exposed_headers ?methods ())
diff --git a/src/extensions/cors.mli b/src/extensions/cors.mli
index 2b873adf8..a604b50e3 100644
--- a/src/extensions/cors.mli
+++ b/src/extensions/cors.mli
@@ -1,7 +1,8 @@
 val run :
-   ?credentials:bool
+   ?site:Ocsigen_server.Site.t
+  -> ?credentials:bool
   -> ?max_age:int
   -> ?exposed_headers:string list
   -> ?methods:Cohttp.Code.meth list
   -> unit
-  -> Ocsigen_server.Site.instruction
+  -> unit
diff --git a/src/extensions/deflatemod.ml b/src/extensions/deflatemod.ml
index 76fe927ba..ed7ce96e3 100644
--- a/src/extensions/deflatemod.ml
+++ b/src/extensions/deflatemod.ml
@@ -366,4 +366,7 @@ let () =
     ~fun_site:(fun _ _ _ _ _ _ -> parse_config)
     ~init_fun:parse_global_config ()
 
-let run ~mode () _ _ _ = filter mode
+let instruction ~mode () _ _ _ = filter mode
+
+let run ?site ~mode () =
+  Ocsigen_server.Site.register ?site (instruction ~mode ())
diff --git a/src/extensions/deflatemod.mli b/src/extensions/deflatemod.mli
index abeb5785f..b9e3a7db7 100644
--- a/src/extensions/deflatemod.mli
+++ b/src/extensions/deflatemod.mli
@@ -7,6 +7,7 @@ val set_buffer_size : int -> unit
 type filter = [`Type of string option * string option | `Extension of string]
 
 val run :
-   mode:[`All_but of filter list | `Only of filter list]
+   ?site:Ocsigen_server.Site.t
+  -> mode:[`All_but of filter list | `Only of filter list]
+  -> unit
   -> unit
-  -> Ocsigen_server.Site.instruction
diff --git a/src/extensions/outputfilter.ml b/src/extensions/outputfilter.ml
index 08167bb0d..30cc1c506 100644
--- a/src/extensions/outputfilter.ml
+++ b/src/extensions/outputfilter.ml
@@ -116,5 +116,8 @@ let () =
     ~fun_site:(fun _ _ _ _ _ _ -> parse_config)
     ()
 
-let run ~mode () _ _ _ =
+let instruction ~mode () _ _ _ =
   match mode with `Code c -> gen_code c | #header_filter as f -> gen f
+
+let run ?site ~mode () =
+  Ocsigen_server.Site.register ?site (instruction ~mode ())
diff --git a/src/extensions/outputfilter.mli b/src/extensions/outputfilter.mli
index d33c9d07b..f1d4ffa40 100644
--- a/src/extensions/outputfilter.mli
+++ b/src/extensions/outputfilter.mli
@@ -1,7 +1,8 @@
 val run :
-   mode:
-     [ `Rewrite of Ocsigen_header.Name.t * Re.Pcre.regexp * string
-     | `Add of Ocsigen_header.Name.t * string * bool option
-     | `Code of Cohttp.Code.status ]
+   ?site:Ocsigen_server.Site.t
+  -> mode:
+       [ `Rewrite of Ocsigen_header.Name.t * Re.Pcre.regexp * string
+       | `Add of Ocsigen_header.Name.t * string * bool option
+       | `Code of Cohttp.Code.status ]
+  -> unit
   -> unit
-  -> Ocsigen_server.Site.instruction
diff --git a/src/extensions/redirectmod.ml b/src/extensions/redirectmod.ml
index 1c65647fd..9912d61e5 100644
--- a/src/extensions/redirectmod.ml
+++ b/src/extensions/redirectmod.ml
@@ -112,4 +112,7 @@ let () =
     ~fun_site:(fun _ _ _ _ _ _ -> parse_config)
     ()
 
-let run ~redirection () _ _ _ = gen redirection
+let instruction ~redirection () _ _ _ = gen redirection
+
+let run ?site ~redirection () =
+  Ocsigen_server.Site.register ?site (instruction ~redirection ())
diff --git a/src/extensions/redirectmod.mli b/src/extensions/redirectmod.mli
index e0f0ecb2d..4c4b15ce9 100644
--- a/src/extensions/redirectmod.mli
+++ b/src/extensions/redirectmod.mli
@@ -10,4 +10,4 @@ val create_redirection :
   -> string
   -> redirection
 
-val run : redirection:redirection -> unit -> Ocsigen_server.Site.instruction
+val run : ?site:Ocsigen_server.Site.t -> redirection:redirection -> unit -> unit
diff --git a/src/extensions/revproxy.ml b/src/extensions/revproxy.ml
index 3143bccd2..79c5d3b43 100644
--- a/src/extensions/revproxy.ml
+++ b/src/extensions/revproxy.ml
@@ -197,4 +197,7 @@ let () =
                               when sending to extensions! *)
     ()
 
-let run ~redirection () _ _ _ = gen redirection
+let instruction ~redirection () _ _ _ = gen redirection
+
+let run ?site ~redirection () =
+  Ocsigen_server.Site.register ?site (instruction ~redirection ())
diff --git a/src/extensions/revproxy.mli b/src/extensions/revproxy.mli
index 2f9c86a67..7e2e5949b 100644
--- a/src/extensions/revproxy.mli
+++ b/src/extensions/revproxy.mli
@@ -11,4 +11,4 @@ val create_redirection :
   -> string
   -> redirection
 
-val run : redirection:redirection -> unit -> Ocsigen_server.Site.instruction
+val run : ?site:Ocsigen_server.Site.t -> redirection:redirection -> unit -> unit
diff --git a/src/extensions/rewritemod.ml b/src/extensions/rewritemod.ml
index a8e272f82..073cdd36a 100644
--- a/src/extensions/rewritemod.ml
+++ b/src/extensions/rewritemod.ml
@@ -128,10 +128,16 @@ let () =
     ~fun_site:(fun _ _ _ _ _ _ -> parse_config)
     ()
 
-let run ?(continue = false) ?(full_rewrite = false) ~regexp dest () _ _ _ =
+let instruction ?(continue = false) ?(full_rewrite = false) ~regexp dest () _ _
+    _
+  =
   gen
     (Regexp
        ( Ocsigen_lib.Netstring_pcre.regexp ("^" ^ regexp ^ "$")
        , dest
        , full_rewrite ))
     continue
+
+let run ?site ?continue ?full_rewrite ~regexp dest () =
+  Ocsigen_server.Site.register ?site
+    (instruction ?continue ?full_rewrite ~regexp dest ())
diff --git a/src/extensions/rewritemod.mli b/src/extensions/rewritemod.mli
index f8cec5173..ba60ae605 100644
--- a/src/extensions/rewritemod.mli
+++ b/src/extensions/rewritemod.mli
@@ -2,9 +2,10 @@ val section : Lwt_log_core.section
 (** use Lwt_log.Section.set_level in order to debug *)
 
 val run :
-   ?continue:bool
+   ?site:Ocsigen_server.Site.t
+  -> ?continue:bool
   -> ?full_rewrite:bool
   -> regexp:string
   -> string
   -> unit
-  -> Ocsigen_server.Site.instruction
+  -> unit
diff --git a/src/extensions/staticmod.ml b/src/extensions/staticmod.ml
index a6af87930..a9bd94ef9 100644
--- a/src/extensions/staticmod.ml
+++ b/src/extensions/staticmod.ml
@@ -281,7 +281,7 @@ let () =
 (* Registration for static linking: *)
 let preprocess s = "^" ^ s ^ "$"
 
-let run ?dir ?regexp ?dest ?code ?cache ?root () =
+let instruction ?dir ?regexp ?dest ?code ?cache ?root () =
   let kind =
     kind dir
       (Ocsigen_lib.Option.map (fun x -> Pcre.regexp (preprocess x)) regexp)
@@ -296,3 +296,7 @@ let run ?dir ?regexp ?dest ?code ?cache ?root () =
          root)
   in
   fun _ _ _ -> gen ~usermode:None ?cache kind
+
+let run ?site ?dir ?regexp ?dest ?code ?cache ?root () =
+  Ocsigen_server.Site.register ?site
+    (instruction ?dir ?regexp ?dest ?code ?cache ?root ())
diff --git a/src/extensions/staticmod.mli b/src/extensions/staticmod.mli
index dff1c1d7e..ac33141f0 100644
--- a/src/extensions/staticmod.mli
+++ b/src/extensions/staticmod.mli
@@ -1,15 +1,15 @@
 val section : Lwt_log_core.section
 (** use Lwt_log.Section.set_level in order to debug *)
 
-(** Use the following config key to set options 
-    for a statically linked executable without configuration file: *)
-
 val run :
-   ?dir:string
+   ?site:Ocsigen_server.Site.t
+  -> ?dir:string
   -> ?regexp:string
   -> ?dest:string
   -> ?code:string
   -> ?cache:int
   -> ?root:string
   -> unit
-  -> Ocsigen_server.Site.instruction
+  -> unit
+(** Run static mod on a specific directory. 
+    Call this if you want to run Ocsigen Server without configuration file. *)
diff --git a/src/server/ocsigen_server.ml b/src/server/ocsigen_server.ml
index 7c96bcfda..8e5983d0a 100644
--- a/src/server/ocsigen_server.ml
+++ b/src/server/ocsigen_server.ml
@@ -151,13 +151,8 @@ module Site = struct
         let path, hosts = path_and_hosts s in
         path @ path', hosts
 
-  let register ({s_config_info; s_children_l; _} as s) f =
-    let path, hosts = path_and_hosts s in
-    s.s_children_l <- `Instruction (f hosts s_config_info path) :: s_children_l
-
   let create ?(config_info = Ocsigen_extensions.default_config_info ())
-      ?(id = `Host (default_re_string, None)) ?charset
-      ()
+      ?(id = `Host (default_re_string, None)) ?charset ()
     =
     let s_id =
       match id with
@@ -170,10 +165,7 @@ module Site = struct
           `Attach (parent, Ocsigen_extensions.preprocess_site_path path)
     in
     let s =
-      { s_id
-      ; s_charset = charset
-      ; s_config_info = config_info
-      ; s_children_l = [] }
+      {s_id; s_charset = charset; s_config_info = config_info; s_children_l = []}
     in
     (match s_id with
     | `Host _ -> l := s :: !l
@@ -181,6 +173,14 @@ module Site = struct
         parent.s_children_l <- `Child s :: parent.s_children_l);
     s
 
+  let default_host = create ()
+
+  let register ?(site = default_host) f =
+    let {s_config_info; s_children_l; _} = site in
+    let path, hosts = path_and_hosts site in
+    site.s_children_l <-
+      `Instruction (f hosts s_config_info path) :: s_children_l
+
   let rec dump_host path {s_children_l; _} =
     let f = function
       | `Instruction f -> f
diff --git a/src/server/ocsigen_server.mli b/src/server/ocsigen_server.mli
index fff04bfcc..89ae13806 100644
--- a/src/server/ocsigen_server.mli
+++ b/src/server/ocsigen_server.mli
@@ -45,6 +45,10 @@ module Site : sig
   This is equivalent to the [<host>] or [<site>] config file options.
   *)
 
+  val default_host : t
+  (** Defaut host. Any hostname, any port.
+      Will be used if you don not specify [?site]. *)
+
   type instruction =
     Ocsigen_extensions.virtual_hosts
     -> Ocsigen_extensions.config_info
@@ -53,6 +57,7 @@ module Site : sig
   (** Instructions are defined by extensions, and correspond to the 
       configuration file options defined by extensions (<staticmod/> ...)*)
 
-  val register : t -> instruction -> unit
-  (** [register t s e] registers instruction [e] to be run inside site [s] *)
+  val register : ?site:t -> instruction -> unit
+  (** [register t s e] registers instruction [e] to be run inside site [s]. 
+      Use this if you want to create an extension yourself. *)
 end