diff --git a/lib_base/time.ml b/lib_base/time.ml
index f5439e1cd..5a92deb65 100644
--- a/lib_base/time.ml
+++ b/lib_base/time.ml
@@ -108,6 +108,19 @@ module T = struct
               (fun i -> i) ;
           ])
 
+  let rpc_arg =
+    RPC_arg.make
+      ~name:(Format.asprintf "date")
+      ~descr:(Format.asprintf "A date in seconds from epoch")
+      ~destruct:
+        (fun s ->
+           match Int64.of_string s with
+           | exception _ ->
+               Error (Format.asprintf "failed to parse time (epoch): %S" s)
+           | v -> Ok v)
+      ~construct:Int64.to_string
+      ()
+
   type 'a timed_data = {
     data: 'a ;
     time: t ;
diff --git a/lib_base/time.mli b/lib_base/time.mli
index 97a0498bd..faab7adfe 100644
--- a/lib_base/time.mli
+++ b/lib_base/time.mli
@@ -40,6 +40,8 @@ val now : unit -> t
 val encoding : t Data_encoding.t
 val rfc_encoding : t Data_encoding.t
 
+val rpc_arg : t RPC_arg.t
+
 val pp_hum : Format.formatter -> t -> unit
 
 type 'a timed_data = {
diff --git a/lib_crypto/blake2B.ml b/lib_crypto/blake2B.ml
index c96c5d217..1418def36 100644
--- a/lib_crypto/blake2B.ml
+++ b/lib_crypto/blake2B.ml
@@ -161,6 +161,21 @@ module Make (R : sig
   let to_short_b58check s =
     String.sub (to_b58check s) 0 (10 + 2 * String.length K.b58check_prefix)
 
+  let rpc_arg =
+    RPC_arg.make
+      ~name:(Format.asprintf "hash.%s" K.name)
+      ~descr:(Format.asprintf "A b58check-encoded hash (%s)" K.name)
+      ~destruct:
+        (fun s ->
+           match of_b58check_opt s with
+           | None ->
+               Error (Format.asprintf
+                        "failed to decode b58check-encoded hash (%s): %S"
+                        K.name s)
+           | Some v -> Ok v)
+      ~construct:to_b58check
+      ()
+
   let encoding =
     let open Data_encoding in
     splitted
diff --git a/lib_crypto/jbuild b/lib_crypto/jbuild
index a7c57c548..778422b61 100644
--- a/lib_crypto/jbuild
+++ b/lib_crypto/jbuild
@@ -6,11 +6,13 @@
   (flags (:standard -open Tezos_stdlib
                     -open Tezos_data_encoding
                     -open Tezos_stdlib_lwt
+                    -open Tezos_rpc_base
                     -open Tezos_error_monad__Error_monad))
   (libraries (tezos-stdlib
               tezos-stdlib-lwt
               tezos-data-encoding
               tezos-error-monad
+              tezos-rpc-base
               nocrypto
               sodium
               zarith))))
diff --git a/lib_crypto/net_id.ml b/lib_crypto/net_id.ml
index e3fe29aca..fa8a4ebc7 100644
--- a/lib_crypto/net_id.ml
+++ b/lib_crypto/net_id.ml
@@ -153,3 +153,16 @@ let zero =
   match of_hex (String.make (size * 2) '0') with
   | Some c -> c
   | None -> assert false
+
+
+let rpc_arg =
+  RPC_arg.make
+    ~name:(Format.asprintf "hash.%s" name)
+    ~descr:(Format.asprintf "A b58check-encoded hash (%s)" name)
+    ~destruct:
+      (fun s ->
+         match of_b58check_opt s with
+         | None -> Error ""
+         | Some v -> Ok v)
+    ~construct:to_b58check
+    ()
diff --git a/lib_crypto/s.ml b/lib_crypto/s.ml
index 2bc08ff01..4375077fa 100644
--- a/lib_crypto/s.ml
+++ b/lib_crypto/s.ml
@@ -72,6 +72,8 @@ module type HASH = sig
   type Base58.data += Hash of t
   val b58check_encoding: t Base58.encoding
 
+  val rpc_arg: t RPC_arg.t
+
   module Set : sig
     include Set.S with type elt = t
     val encoding: t Data_encoding.t
diff --git a/lib_crypto/tezos-crypto.opam b/lib_crypto/tezos-crypto.opam
index 1f6188483..ba2039a05 100644
--- a/lib_crypto/tezos-crypto.opam
+++ b/lib_crypto/tezos-crypto.opam
@@ -13,6 +13,7 @@ depends: [
   "tezos-stdlib-lwt"
   "tezos-data-encoding"
   "tezos-error-monad"
+  "tezos-rpc-base"
   "nocrypto"
   "sodium"
   "zarith"
diff --git a/lib_embedded_protocol_alpha/src/services.ml b/lib_embedded_protocol_alpha/src/services.ml
index 78ed962eb..f7f9209f4 100644
--- a/lib_embedded_protocol_alpha/src/services.ml
+++ b/lib_embedded_protocol_alpha/src/services.ml
@@ -266,18 +266,7 @@ module Context = struct
 
   module Key = struct
 
-    let public_key_hash_arg =
-      let construct = Ed25519.Public_key_hash.to_b58check in
-      let destruct hash =
-        match Ed25519.Public_key_hash.of_b58check_opt hash with
-        | None -> Error "Cannot parse public key hash"
-        | Some public_key_hash -> Ok public_key_hash in
-      RPC_arg.make
-        ~descr:"A public key hash"
-        ~name: "public_key_hash"
-        ~construct
-        ~destruct
-        ()
+    let public_key_hash_arg = Ed25519.Public_key_hash.rpc_arg
 
     let pk_encoding =
       (obj2
diff --git a/lib_node_services/node_rpc_services.ml b/lib_node_services/node_rpc_services.ml
index 3c89deada..510efc88a 100644
--- a/lib_node_services/node_rpc_services.ml
+++ b/lib_node_services/node_rpc_services.ml
@@ -459,15 +459,7 @@ end
 
 module Protocols = struct
 
-  let protocols_arg =
-    let name = "protocol_id" in
-    let descr =
-      "A protocol identifier in hexadecimal." in
-    let construct = Protocol_hash.to_b58check in
-    let destruct h =
-      try Ok (Protocol_hash.of_b58check_exn h)
-      with _ -> Error "Can't parse hash" in
-    RPC_arg.make ~name ~descr ~construct ~destruct ()
+  let protocols_arg = Protocol_hash.rpc_arg
 
   let contents =
     RPC_service.post_service
@@ -516,14 +508,7 @@ module Network = struct
   open P2p_types
 
   let (peer_id_arg : P2p_types.Peer_id.t RPC_arg.arg) =
-    RPC_arg.make
-      ~name:"peer_id"
-      ~descr:"A network global identifier, also known as an identity."
-      ~destruct:(fun s -> try
-                    Ok (Crypto_box.Public_key_hash.of_b58check_exn s)
-                  with Failure msg -> Error msg)
-      ~construct:Crypto_box.Public_key_hash.to_b58check
-      ()
+    Crypto_box.Public_key_hash.rpc_arg
 
   let point_arg =
     RPC_arg.make
diff --git a/lib_protocol_environment_sigs/jbuild b/lib_protocol_environment_sigs/jbuild
index 2dda4d5cf..44cb698e5 100644
--- a/lib_protocol_environment_sigs/jbuild
+++ b/lib_protocol_environment_sigs/jbuild
@@ -29,23 +29,25 @@
     v1/compare.mli
     v1/data_encoding.mli
     v1/error_monad.mli
-    v1/micheline.mli
     v1/logging.mli
     v1/time.mli
-    v1/base58.mli
-    v1/hash.mli
-    v1/blake2B.mli
-    v1/ed25519.mli
 
-    ;; Tezos specifics
-    v1/tezos_data.mli
-    v1/context.mli
     v1/RPC_arg.mli
     v1/RPC_path.mli
     v1/RPC_query.mli
     v1/RPC_service.mli
     v1/RPC_answer.mli
     v1/RPC_directory.mli
+
+    v1/base58.mli
+    v1/hash.mli
+    v1/blake2B.mli
+    v1/ed25519.mli
+
+    ;; Tezos specifics
+    v1/micheline.mli
+    v1/tezos_data.mli
+    v1/context.mli
     v1/updater.mli
 
   ))
diff --git a/lib_protocol_environment_sigs/v1/hash.mli b/lib_protocol_environment_sigs/v1/hash.mli
index bf08c72b1..b8306049e 100644
--- a/lib_protocol_environment_sigs/v1/hash.mli
+++ b/lib_protocol_environment_sigs/v1/hash.mli
@@ -68,6 +68,8 @@ module type HASH = sig
   type Base58.data += Hash of t
   val b58check_encoding: t Base58.encoding
 
+  val rpc_arg: t RPC_arg.t
+
   module Set : sig
     include Set.S with type elt = t
     val encoding: t Data_encoding.t