diff --git a/src/SimpleHTTPServer.ml b/src/SimpleHTTPServer.ml
index c8b22638..683528f9 100644
--- a/src/SimpleHTTPServer.ml
+++ b/src/SimpleHTTPServer.ml
@@ -149,12 +149,16 @@ type t = {
   masksigpipe: bool;
   mutable handler: (Request.t -> Response.t);
   mutable path_handlers : (Request.t -> (unit -> Response.t) option) list;
+  mutable req_cbs: (Request.t -> Request.t option) list;
+  mutable res_cbs: (Request.t -> Response.t -> Response.t option) list;
   mutable running: bool;
 }
 
 let addr self = self.addr
 let port self = self.port
 
+let add_request_cb self f =  self.req_cbs <- f :: self.req_cbs
+let add_response_cb self f = self.res_cbs <- f :: self.res_cbs
 let set_top_handler self f = self.handler <- f
 
 let add_path_handler ?meth self fmt f =
@@ -173,7 +177,9 @@ let create
     ?(addr="127.0.0.1") ?(port=8080) () : t =
   let handler _req = Response.make_not_found "no top handler" in
   { fork; addr; port; masksigpipe; handler; running= true;
-    path_handlers=[]; }
+    path_handlers=[];
+    req_cbs=[]; res_cbs=[];
+  }
 
 let stop s = s.running <- false
 
@@ -200,12 +206,23 @@ let handle_client_ (self:t) (client_sock:Unix.file_descr) : unit =
       Response.output_ oc res
     | Ok (Some req) ->
       let res =
-        let run_handler =
-          match find_map (fun ph -> ph req) ph_handlers with
-          | Some f -> f
-          | None -> (fun () -> handler req)
-        in
-        try run_handler()
+        try
+          (* request callbacks *)
+          let req =
+            List.fold_left
+              (fun req cb -> match cb req with None -> req | Some r' -> r')
+              req self.req_cbs
+          in
+          let run_handler =
+            match find_map (fun ph -> ph req) ph_handlers with
+            | Some f -> f
+            | None -> (fun () -> handler req)
+          in
+          let resp = run_handler() in
+          (* response callbacks *)
+          List.fold_left
+            (fun resp cb -> match cb req resp with None -> resp | Some r' -> r')
+            resp self.res_cbs
         with
         | e ->
           Response.make ~code:500 ("server error: " ^ Printexc.to_string e)
diff --git a/src/SimpleHTTPServer.mli b/src/SimpleHTTPServer.mli
index f87d98da..6820fe42 100644
--- a/src/SimpleHTTPServer.mli
+++ b/src/SimpleHTTPServer.mli
@@ -17,7 +17,12 @@ module Headers : sig
 end
 
 module Request : sig
-  type t
+  type t = {
+    meth: Meth.t;
+    headers: Headers.t;
+    path: string;
+    body: string
+  }
 
   val pp : Format.formatter -> t -> unit
 
@@ -62,6 +67,16 @@ val create :
 
 val addr : t -> string
 val port : t -> int
+
+val add_request_cb : t -> (Request.t -> Request.t option) -> unit
+(** Add a callback for every request.
+    The callback can modify the request by returning [Some r'] where [r']
+    is the new request, or just perform side effects (logging?) and return [None].
+*)
+
+val add_response_cb : t -> (Request.t -> Response.t -> Response.t option) -> unit
+(** Add a callback for every request/response pair.
+    Similarly to {!add_request_cb} the callback can modify the response. *)
   
 val set_top_handler : t -> (Request.t -> Response.t) -> unit
 (** Setup a handler called by default.