diff --git a/src/irmin-graphql/irmin_graphql.ml b/src/irmin-graphql/irmin_graphql.ml
index 6e3e589aaec..7ec4efd106e 100644
--- a/src/irmin-graphql/irmin_graphql.ml
+++ b/src/irmin-graphql/irmin_graphql.ml
@@ -1,17 +1,24 @@
 open Lwt.Infix
 
 module Schema = Graphql_lwt.Schema
-module Graphql_server = Graphql_cohttp.Make(Schema)(Cohttp_lwt.Body)
 
 module type S = sig
+  module IO : Cohttp_lwt.S.IO
   type store
   type server
 
+  type response_action =
+    [ `Expert of Cohttp.Response.t
+                 * (IO.ic
+                    -> IO.oc
+                    -> unit Lwt.t)
+    | `Response of Cohttp.Response.t * Cohttp_lwt.Body.t ]
+
   val schema : store -> unit Schema.schema
   val execute_request :
     unit Schema.schema ->
     Cohttp_lwt.Request.t ->
-    Cohttp_lwt.Body.t -> (Cohttp.Response.t * Cohttp_lwt.Body.t) Lwt.t
+    Cohttp_lwt.Body.t -> response_action Lwt.t
   val server : store -> server
 end
 
@@ -30,7 +37,16 @@ module type CONFIG = sig
 end
 
 module Make(Server: Cohttp_lwt.S.Server)(Config: CONFIG)(Store : Irmin.S) = struct
+  module IO = Server.IO
   module Sync = Irmin.Sync (Store)
+  module Graphql_server = Graphql_cohttp.Make(Schema)(IO)(Cohttp_lwt.Body)
+
+  type response_action =
+    [ `Expert of Cohttp.Response.t
+                 * (IO.ic
+                    -> IO.oc
+                    -> unit Lwt.t)
+    | `Response of Cohttp.Response.t * Cohttp_lwt.Body.t ]
 
   type tree_item = {
     key: Store.key;
@@ -542,9 +558,60 @@ module Make(Server: Cohttp_lwt.S.Server)(Config: CONFIG)(Store : Irmin.S) = stru
       ;
     ]
 
+  let diff = Schema.(obj "Diff"
+    ~fields:(fun _ -> [
+      field "commit"
+        ~typ:(non_null Lazy.(force commit))
+        ~args:[]
+        ~resolve:(fun _ctx -> function
+          | `Added c
+          | `Removed c
+          | `Updated (_, c) -> c
+        )
+    ])
+  )
+
+  let map_diff diff ~added ~removed ~updated =
+    match diff with
+    | `Added x -> `Added (added x)
+    | `Removed x -> `Removed (removed x)
+    | `Updated (x, y) -> `Updated (updated x y)
+
+  let subscriptions s = Schema.[
+    subscription_field "watch"
+      ~typ:(non_null diff)
+      ~args:Arg.[
+        arg "key" ~typ:Input.key
+      ]
+      ~resolve:(fun _ctx key ->
+        let stream, push = Lwt_stream.create () in
+        let destroy_stream watch () =
+          push None;
+          Lwt.ignore_result (Store.unwatch watch)
+        in
+        match key with
+        | None ->
+          Store.watch s (fun diff ->
+            push (Some diff);
+            Lwt.return ()
+          ) >|= fun watch ->
+          Ok (stream, destroy_stream watch)
+        | Some key ->
+          Store.watch_key s key (function diff ->
+            push (Some (map_diff diff
+              ~added:(fun (c, _) -> c)
+              ~removed:(fun (c, _) -> c)
+              ~updated:(fun (before, _) (after, _) -> before, after)));
+            Lwt.return ()
+          ) >|= fun watch ->
+          Ok (stream, destroy_stream watch)
+      )
+  ]
+
   let schema s =
     let mutations = mutations s @ remote s in
-    Schema.(schema ~mutations [
+    let subscriptions = subscriptions s in
+    Schema.(schema ~mutations ~subscriptions [
         io_field "commit"
           ~typ:(Lazy.force commit)
           ~args:Arg.[
@@ -583,5 +650,5 @@ module Make(Server: Cohttp_lwt.S.Server)(Config: CONFIG)(Store : Irmin.S) = stru
   let server store =
     let schema = schema store in
     let callback = Graphql_server.make_callback (fun _ctx -> ()) schema in
-    Server.make ~callback ()
+    Server.make_response_action ~callback ()
 end
diff --git a/src/irmin-graphql/irmin_graphql.mli b/src/irmin-graphql/irmin_graphql.mli
index becad0ff5d6..49042aaf613 100644
--- a/src/irmin-graphql/irmin_graphql.mli
+++ b/src/irmin-graphql/irmin_graphql.mli
@@ -1,14 +1,22 @@
 module Schema : Graphql_intf.Schema with type 'a Io.t = 'a Lwt.t
 
 module type S = sig
+  module IO : Cohttp_lwt.S.IO
   type store
   type server
 
+  type response_action =
+    [ `Expert of Cohttp.Response.t
+                 * (IO.ic
+                    -> IO.oc
+                    -> unit Lwt.t)
+    | `Response of Cohttp.Response.t * Cohttp_lwt.Body.t ]
+
   val schema : store -> unit Schema.schema
   val execute_request :
       unit Schema.schema ->
       Cohttp_lwt.Request.t ->
-      Cohttp_lwt.Body.t -> (Cohttp.Response.t * Cohttp_lwt.Body.t) Lwt.t
+      Cohttp_lwt.Body.t -> response_action Lwt.t
   val server : store -> server
 end