diff --git a/src/lib_shell/node_rpc.ml b/src/lib_shell/node_rpc.ml
index add189143..49a7d8373 100644
--- a/src/lib_shell/node_rpc.ml
+++ b/src/lib_shell/node_rpc.ml
@@ -449,14 +449,14 @@ let build_rpc_directory node =
   (* Workers : Prevalidators *)
 
   let dir  =
-    RPC_directory.register0 dir Worker_services.Prevalidators.list
+    RPC_directory.register0 dir Worker_services.Prevalidators.S.list
       (fun () () ->
          RPC_answer.return
            (List.map
               (fun (id, w) -> (id, Prevalidator.status w))
               (Prevalidator.running_workers ()))) in
   let dir  =
-    RPC_directory.register1 dir Worker_services.Prevalidators.state
+    RPC_directory.register1 dir Worker_services.Prevalidators.S.state
       (fun net_id () () ->
          let w = List.assoc net_id (Prevalidator.running_workers ()) in
          RPC_answer.return
@@ -468,7 +468,7 @@ let build_rpc_directory node =
   (* Workers : Block_validator *)
 
   let dir  =
-    RPC_directory.register0 dir Worker_services.Block_validator.state
+    RPC_directory.register0 dir Worker_services.Block_validator.S.state
       (fun () () ->
          let w = Block_validator.running_worker () in
          RPC_answer.return
@@ -480,7 +480,7 @@ let build_rpc_directory node =
   (* Workers : Peer validators *)
 
   let dir  =
-    RPC_directory.register1 dir Worker_services.Peer_validators.list
+    RPC_directory.register1 dir Worker_services.Peer_validators.S.list
       (fun net_id () () ->
          RPC_answer.return
            (List.filter_map
@@ -490,7 +490,7 @@ let build_rpc_directory node =
                  else None)
               (Peer_validator.running_workers ()))) in
   let dir  =
-    RPC_directory.register2 dir Worker_services.Peer_validators.state
+    RPC_directory.register2 dir Worker_services.Peer_validators.S.state
       (fun net_id peer_id () () ->
          let w = List.assoc (net_id, peer_id) (Peer_validator.running_workers ()) in
          RPC_answer.return
@@ -502,14 +502,14 @@ let build_rpc_directory node =
   (* Workers : Net validators *)
 
   let dir  =
-    RPC_directory.register0 dir Worker_services.Net_validators.list
+    RPC_directory.register0 dir Worker_services.Net_validators.S.list
       (fun () () ->
          RPC_answer.return
            (List.map
               (fun (id, w) -> (id, Net_validator.status w))
               (Net_validator.running_workers ()))) in
   let dir  =
-    RPC_directory.register1 dir Worker_services.Net_validators.state
+    RPC_directory.register1 dir Worker_services.Net_validators.S.state
       (fun net_id () () ->
          let w = List.assoc net_id (Net_validator.running_workers ()) in
          RPC_answer.return
diff --git a/src/lib_shell_services/worker_services.ml b/src/lib_shell_services/worker_services.ml
index fb611b29c..8303aa77c 100644
--- a/src/lib_shell_services/worker_services.ml
+++ b/src/lib_shell_services/worker_services.ml
@@ -11,144 +11,162 @@ open Data_encoding
 
 module Prevalidators = struct
 
-  let (net_id_arg : Net_id.t RPC_arg.t) =
-    RPC_arg.make
-      ~name:"net_id"
-      ~descr:"The network identifier of whom the prevalidator is responsible."
-      ~destruct:(fun s -> try
-                    Ok (Net_id.of_b58check_exn s)
-                  with Failure msg -> Error msg)
-      ~construct:Net_id.to_b58check
-      ()
+  module S = struct
 
-  let list =
-    RPC_service.post_service
-      ~description:"Lists the Prevalidator workers and their status."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (list
-           (obj2
-              (req "net_id" Net_id.encoding)
-              (req "status" (Worker_types.worker_status_encoding  RPC_error.encoding))))
-      RPC_path.(root / "workers" / "prevalidators")
+    let (net_id_arg : Net_id.t RPC_arg.t) =
+      RPC_arg.like
+        Net_id.rpc_arg
+        ~descr:"The network identifier of whom the prevalidator is responsible."
+        "net_id"
 
-  let state =
-    let open Data_encoding in
-    RPC_service.post_service
-      ~description:"Introspect the state of a prevalidator worker."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (Worker_types.full_status_encoding
-           Prevalidator_worker_state.Request.encoding
-           Prevalidator_worker_state.Event.encoding
-           RPC_error.encoding)
-      RPC_path.(root / "workers" / "prevalidators" /: net_id_arg )
+    let list =
+      RPC_service.post_service
+        ~description:"Lists the Prevalidator workers and their status."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (list
+             (obj2
+                (req "net_id" Net_id.encoding)
+                (req "status" (Worker_types.worker_status_encoding  RPC_error.encoding))))
+        RPC_path.(root / "workers" / "prevalidators")
+
+    let state =
+      let open Data_encoding in
+      RPC_service.post_service
+        ~description:"Introspect the state of a prevalidator worker."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (Worker_types.full_status_encoding
+             Prevalidator_worker_state.Request.encoding
+             Prevalidator_worker_state.Event.encoding
+             RPC_error.encoding)
+        RPC_path.(root / "workers" / "prevalidators" /: Net_id.rpc_arg )
+
+  end
+
+  open RPC_context
+  let list ctxt = make_call S.list ctxt () () ()
+  let state ctxt h = make_call1 S.state ctxt h () ()
 
 end
 
 module Block_validator = struct
 
-  let state =
-    let open Data_encoding in
-    RPC_service.post_service
-      ~description:"Introspect the state of the block_validator worker."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (Worker_types.full_status_encoding
-           Block_validator_worker_state.Request.encoding
-           Block_validator_worker_state.Event.encoding
-           RPC_error.encoding)
-      RPC_path.(root / "workers" / "block_validator")
+  module S = struct
+
+    let state =
+      let open Data_encoding in
+      RPC_service.post_service
+        ~description:"Introspect the state of the block_validator worker."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (Worker_types.full_status_encoding
+             Block_validator_worker_state.Request.encoding
+             Block_validator_worker_state.Event.encoding
+             RPC_error.encoding)
+        RPC_path.(root / "workers" / "block_validator")
+
+  end
+
+  open RPC_context
+  let state ctxt = make_call S.state ctxt () () ()
 
 end
 
 module Peer_validators = struct
 
-  let (net_id_arg : Net_id.t RPC_arg.t) =
-    RPC_arg.make
-      ~name:"net_id"
-      ~descr:"The network identifier the peer validator is associated to."
-      ~destruct:(fun s -> try
-                    Ok (Net_id.of_b58check_exn s)
-                  with Failure msg -> Error msg)
-      ~construct:Net_id.to_b58check
-      ()
+  module S = struct
 
-  let (peer_id_arg : P2p_peer.Id.t RPC_arg.t) =
-    RPC_arg.make
-      ~name:"peer_id"
-      ~descr:"The peer identifier of whom the prevalidator is responsible."
-      ~destruct:(fun s -> try
-                    Ok (P2p_peer.Id.of_b58check_exn s)
-                  with Failure msg -> Error msg)
-      ~construct:P2p_peer.Id.to_b58check
-      ()
+    let (net_id_arg : Net_id.t RPC_arg.t) =
+      RPC_arg.like
+        Net_id.rpc_arg
+        ~descr:"The network identifier the peer validator is associated to."
+        "net_id"
 
-  let list =
-    RPC_service.post_service
-      ~description:"Lists the peer validator workers and their status."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (list
-           (obj2
-              (req "peer_id" P2p_peer.Id.encoding)
-              (req "status" (Worker_types.worker_status_encoding RPC_error.encoding))))
-      RPC_path.(root / "workers" / "peer_validators" /: net_id_arg)
+    let (peer_id_arg : P2p_peer.Id.t RPC_arg.t) =
+      RPC_arg.make
+        ~name:"peer_id"
+        ~descr:"The peer identifier of whom the prevalidator is responsible."
+        ~destruct:(fun s -> try
+                      Ok (P2p_peer.Id.of_b58check_exn s)
+                    with Failure msg -> Error msg)
+        ~construct:P2p_peer.Id.to_b58check
+        ()
 
-  let state =
-    let open Data_encoding in
-    RPC_service.post_service
-      ~description:"Introspect the state of a peer validator worker."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (Worker_types.full_status_encoding
-           Peer_validator_worker_state.Request.encoding
-           Peer_validator_worker_state.Event.encoding
-           RPC_error.encoding)
-      RPC_path.(root / "workers" / "peer_validators" /: net_id_arg /: peer_id_arg)
+    let list =
+      RPC_service.post_service
+        ~description:"Lists the peer validator workers and their status."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (list
+             (obj2
+                (req "peer_id" P2p_peer.Id.encoding)
+                (req "status" (Worker_types.worker_status_encoding RPC_error.encoding))))
+        RPC_path.(root / "workers" / "peer_validators" /: net_id_arg)
+
+    let state =
+      let open Data_encoding in
+      RPC_service.post_service
+        ~description:"Introspect the state of a peer validator worker."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (Worker_types.full_status_encoding
+             Peer_validator_worker_state.Request.encoding
+             Peer_validator_worker_state.Event.encoding
+             RPC_error.encoding)
+        RPC_path.(root / "workers" / "peer_validators" /: net_id_arg /: peer_id_arg)
+
+  end
+
+  open RPC_context
+  let list ctxt n = make_call1 S.list ctxt n () ()
+  let state ctxt n h = make_call2 S.state ctxt n h () ()
 
 end
 
 module Net_validators = struct
 
-  let (net_id_arg : Net_id.t RPC_arg.t) =
-    RPC_arg.make
-      ~name:"net_id"
-      ~descr:"The network identifier of whom the net validator is responsible."
-      ~destruct:(fun s -> try
-                    Ok (Net_id.of_b58check_exn s)
-                  with Failure msg -> Error msg)
-      ~construct:Net_id.to_b58check
-      ()
+  module S = struct
+    let (net_id_arg : Net_id.t RPC_arg.t) =
+      RPC_arg.like
+        Net_id.rpc_arg
+        ~descr:"The network identifier of whom the net validator is responsible."
+        "net_id"
 
-  let list =
-    RPC_service.post_service
-      ~description:"Lists the net validator workers and their status."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (list
-           (obj2
-              (req "net_id" Net_id.encoding)
-              (req "status" (Worker_types.worker_status_encoding RPC_error.encoding))))
-      RPC_path.(root / "workers" / "net_validators")
+    let list =
+      RPC_service.post_service
+        ~description:"Lists the net validator workers and their status."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (list
+             (obj2
+                (req "net_id" Net_id.encoding)
+                (req "status" (Worker_types.worker_status_encoding RPC_error.encoding))))
+        RPC_path.(root / "workers" / "net_validators")
 
-  let state =
-    let open Data_encoding in
-    RPC_service.post_service
-      ~description:"Introspect the state of a net validator worker."
-      ~query: RPC_query.empty
-      ~input: empty
-      ~output:
-        (Worker_types.full_status_encoding
-           Net_validator_worker_state.Request.encoding
-           Net_validator_worker_state.Event.encoding
-           RPC_error.encoding)
-      RPC_path.(root / "workers" / "net_validators" /: net_id_arg )
+    let state =
+      let open Data_encoding in
+      RPC_service.post_service
+        ~description:"Introspect the state of a net validator worker."
+        ~query: RPC_query.empty
+        ~input: empty
+        ~output:
+          (Worker_types.full_status_encoding
+             Net_validator_worker_state.Request.encoding
+             Net_validator_worker_state.Event.encoding
+             RPC_error.encoding)
+        RPC_path.(root / "workers" / "net_validators" /: net_id_arg )
+
+  end
+
+  open RPC_context
+  let list ctxt = make_call S.list ctxt () () ()
+  let state ctxt h = make_call1 S.state ctxt h () ()
 
 end
diff --git a/src/lib_shell_services/worker_services.mli b/src/lib_shell_services/worker_services.mli
index b479dddeb..7c412d63e 100644
--- a/src/lib_shell_services/worker_services.mli
+++ b/src/lib_shell_services/worker_services.mli
@@ -7,19 +7,30 @@
 (*                                                                        *)
 (**************************************************************************)
 
+open RPC_context
+
 module Prevalidators : sig
 
   open Prevalidator_worker_state
 
-  val list :
-    ([ `POST ],  unit,
-     unit, unit, unit,
-     (Net_id.t * Worker_types.worker_status) list) RPC_service.t
+  val list:
+    #simple -> (Net_id.t * Worker_types.worker_status) list tzresult Lwt.t
+  val state:
+    #simple -> Net_id.t -> (Request.view, Event.t) Worker_types.full_status tzresult Lwt.t
 
-  val state :
-    ([ `POST ], unit,
-     unit * Net_id.t, unit, unit,
-     (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+  module S : sig
+
+    val list :
+      ([ `POST ],  unit,
+       unit, unit, unit,
+       (Net_id.t * Worker_types.worker_status) list) RPC_service.t
+
+    val state :
+      ([ `POST ], unit,
+       unit * Net_id.t, unit, unit,
+       (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+
+  end
 
 end
 
@@ -27,10 +38,17 @@ module Block_validator : sig
 
   open Block_validator_worker_state
 
-  val state :
-    ([ `POST ], unit,
-     unit, unit, unit,
-     (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+  val state:
+    #simple -> (Request.view, Event.t) Worker_types.full_status tzresult Lwt.t
+
+  module S : sig
+
+    val state :
+      ([ `POST ], unit,
+       unit, unit, unit,
+       (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+
+  end
 
 end
 
@@ -38,15 +56,27 @@ module Peer_validators : sig
 
   open Peer_validator_worker_state
 
-  val list :
-    ([ `POST ],  unit,
-     unit * Net_id.t, unit, unit,
-     (P2p_peer.Id.t * Worker_types.worker_status) list) RPC_service.t
+  val list:
+    #simple -> Net_id.t ->
+    (P2p_peer.Id.t * Worker_types.worker_status) list tzresult Lwt.t
 
-  val state :
-    ([ `POST ], unit,
-     (unit * Net_id.t) * P2p_peer.Id.t, unit, unit,
-     (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+  val state:
+    #simple ->
+    Net_id.t -> P2p_peer.Id.t -> (Request.view, Event.t) Worker_types.full_status tzresult Lwt.t
+
+  module S : sig
+
+    val list :
+      ([ `POST ],  unit,
+       unit * Net_id.t, unit, unit,
+       (P2p_peer.Id.t * Worker_types.worker_status) list) RPC_service.t
+
+    val state :
+      ([ `POST ], unit,
+       (unit * Net_id.t) * P2p_peer.Id.t, unit, unit,
+       (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+
+  end
 
 end
 
@@ -54,14 +84,23 @@ module Net_validators : sig
 
   open Net_validator_worker_state
 
-  val list :
-    ([ `POST ],  unit,
-     unit, unit, unit,
-     (Net_id.t * Worker_types.worker_status) list) RPC_service.t
+  val list:
+    #simple -> (Net_id.t * Worker_types.worker_status) list tzresult Lwt.t
+  val state:
+    #simple -> Net_id.t -> (Request.view, Event.t) Worker_types.full_status tzresult Lwt.t
 
-  val state :
-    ([ `POST ], unit,
-     unit * Net_id.t, unit, unit,
-     (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+  module S : sig
+
+    val list :
+      ([ `POST ],  unit,
+       unit, unit, unit,
+       (Net_id.t * Worker_types.worker_status) list) RPC_service.t
+
+    val state :
+      ([ `POST ], unit,
+       unit * Net_id.t, unit, unit,
+       (Request.view, Event.t) Worker_types.full_status) RPC_service.t
+
+  end
 
 end