diff --git a/src/bin_dal_node/RPC_server.ml b/src/bin_dal_node/RPC_server.ml
index c913a33bc7d4a38280f52cbc5a90282d75ed1dc1..ce6bff0f3e18a96fda789b9abd4495b320674b68 100644
--- a/src/bin_dal_node/RPC_server.ml
+++ b/src/bin_dal_node/RPC_server.ml
@@ -32,7 +32,6 @@ open Tezos_dal_node_services
 let handle_split_slot ctxt fill slot =
   let open Lwt_result_syntax in
   let*? {dal_parameters; dal_constants; _} = Node_context.get_ready ctxt in
-  let slot = String.to_bytes slot in
   let slot =
     if fill then
       Slot_manager.Utils.fill_x00 dal_parameters.Cryptobox.slot_size slot
@@ -59,7 +58,7 @@ let handle_slot ctxt (_, commitment) trim () =
       commitment
   in
   let slot = if trim then Slot_manager.Utils.trim_x00 slot else slot in
-  return (String.of_bytes slot)
+  return slot
 
 let handle_stored_slot_headers ctxt (_, block_hash) () () =
   let open Lwt_result_syntax in
diff --git a/src/lib_dal_node/dal_node_client.mli b/src/lib_dal_node/dal_node_client.mli
index 26c019f4697ee6ad6aab8d63ce406141032da1c4..ae69e9265394b338a9f4c8349c4bdb2113d746ca 100644
--- a/src/lib_dal_node/dal_node_client.mli
+++ b/src/lib_dal_node/dal_node_client.mli
@@ -42,7 +42,7 @@ class unix_cctxt :
 val make_unix_cctxt : addr:string -> port:int -> cctxt
 
 val get_slot :
-  #cctxt -> ?trim_slot:bool -> Cryptobox.Commitment.t -> string tzresult Lwt.t
+  #cctxt -> ?trim_slot:bool -> Cryptobox.Commitment.t -> bytes tzresult Lwt.t
 
 val get_shard :
   #cctxt -> Cryptobox.Commitment.t -> int -> Cryptobox.shard tzresult Lwt.t
diff --git a/src/lib_dal_node_services/services.ml b/src/lib_dal_node_services/services.ml
index a1d8ddf28cc12c9ef07c917ff7311a1e7181a8dd..b137dcc89d8ef25cb00c764c0f3a3aa86ac318d0 100644
--- a/src/lib_dal_node_services/services.ml
+++ b/src/lib_dal_node_services/services.ml
@@ -34,7 +34,7 @@ let split_slot () =
   RPC_service.post_service
     ~description:"Split and store a slot"
     ~query:split_query
-    ~input:Data_encoding.string
+    ~input:Data_encoding.bytes
     ~output:Data_encoding.string
       (* see [Slot_manager.Slot_header.to_b58check] *)
     RPC_path.(open_root / "slot" / "split")
@@ -49,7 +49,7 @@ let slot () =
   RPC_service.get_service
     ~description:"Show content of a slot"
     ~query:slot_query
-    ~output:Data_encoding.string
+    ~output:Data_encoding.bytes
     RPC_path.(open_root / "slot" / "content" /: Cryptobox.Commitment.rpc_arg)
 
 let slot_pages () =
diff --git a/tezt/lib_tezos/rollup.ml b/tezt/lib_tezos/rollup.ml
index 0812760c51bf4085db4a221eb336a0dd433f9a24..47882229ee75d0ba97680b82fe0042a767470b5b 100644
--- a/tezt/lib_tezos/rollup.ml
+++ b/tezt/lib_tezos/rollup.ml
@@ -540,11 +540,20 @@ module Dal = struct
         ~get_host:Dal_node.rpc_host
         ~get_port:Dal_node.rpc_port
 
+    (** [encode_bytes_for_json raw] encodes arbitrary byte sequence as hex string for JSON *)
+    let encode_bytes_to_hex_string raw =
+      "\"" ^ match Hex.of_string raw with `Hex s -> s ^ "\""
+
+    let decode_hex_string_to_bytes s = Hex.to_string (`Hex s)
+
+    let get_bytes_from_json_string_node json =
+      JSON.as_string json |> decode_hex_string_to_bytes
+
     let split_slot slot =
       let slot =
         JSON.parse
           ~origin:"dal_node_split_slot_rpc"
-          (Format.sprintf "\"%s\"" slot)
+          (encode_bytes_to_hex_string slot)
       in
       let data = JSON.unannotate slot in
       make
@@ -559,11 +568,11 @@ module Dal = struct
         GET
         ["slot"; "content"; slot_header]
         ~query_string:[("trim", "")]
-        JSON.as_string
+        get_bytes_from_json_string_node
 
     let slot_pages slot_header =
       make GET ["slot"; "pages"; slot_header] (fun pages ->
-          pages |> JSON.as_list |> List.map JSON.as_string)
+          pages |> JSON.as_list |> List.map get_bytes_from_json_string_node)
 
     let stored_slot_headers block_hash =
       make GET ["stored_slot_headers"; block_hash] @@ fun json ->
diff --git a/tezt/tests/dal.ml b/tezt/tests/dal.ml
index bd8b8516654bb3d289aa6f368665e1ab5f0ddf6f..1e7bc20855229ec7d1f9e1d02406987a1bef1789 100644
--- a/tezt/tests/dal.ml
+++ b/tezt/tests/dal.ml
@@ -498,6 +498,8 @@ let init_dal_node protocol =
   let* () = Dal_node.run dal_node in
   return (node, client, dal_node)
 
+let split_slot node slot = RPC.call node (Rollup.Dal.RPC.split_slot slot)
+
 let test_dal_node_slot_management =
   Protocol.register_test
     ~__FILE__
@@ -506,10 +508,8 @@ let test_dal_node_slot_management =
     ~supports:Protocol.(From_protocol (Protocol.number Alpha))
   @@ fun protocol ->
   let* _node, _client, dal_node = init_dal_node protocol in
-  let slot_content = "test" in
-  let* slot_header =
-    RPC.call dal_node (Rollup.Dal.RPC.split_slot slot_content)
-  in
+  let slot_content = "test with invalid UTF-8 byte sequence \xFA" in
+  let* slot_header = split_slot dal_node slot_content in
   let* received_slot_content =
     RPC.call dal_node (Rollup.Dal.RPC.slot_content slot_header)
   in
@@ -522,7 +522,7 @@ let test_dal_node_slot_management =
   return ()
 
 let publish_and_store_slot node client dal_node source index content =
-  let* slot_header = RPC.call dal_node (Rollup.Dal.RPC.split_slot content) in
+  let* slot_header = split_slot dal_node content in
   let commitment =
     Tezos_crypto_dal.Cryptobox.Commitment.of_b58check_opt slot_header
     |> mandatory "The b58check-encoded slot header is not valid"
@@ -635,12 +635,8 @@ let test_dal_node_test_slots_propagation =
   let* () = Dal_node.run dal_node2 in
   let* () = Dal_node.run dal_node3 in
   let* () = Dal_node.run dal_node4 in
-  let* slot_header1 =
-    RPC.call dal_node1 (Rollup.Dal.RPC.split_slot "content1")
-  in
-  let* slot_header2 =
-    RPC.call dal_node2 (Rollup.Dal.RPC.split_slot "content2")
-  in
+  let* slot_header1 = split_slot dal_node1 "content1" in
+  let* slot_header2 = split_slot dal_node2 "content2" in
   Lwt.join
     [
       wait_for_stored_slot dal_node3 slot_header1;
@@ -714,17 +710,11 @@ let rollup_node_stores_dal_slots ?expand_test _protocol dal_node sc_rollup_node
 
   (* 1. Send three slots to dal node and obtain corresponding headers. *)
   let slot_contents_0 = " 10 " in
-  let* commitment_0 =
-    RPC.call dal_node (Rollup.Dal.RPC.split_slot slot_contents_0)
-  in
+  let* commitment_0 = split_slot dal_node slot_contents_0 in
   let slot_contents_1 = " 200 " in
-  let* commitment_1 =
-    RPC.call dal_node (Rollup.Dal.RPC.split_slot slot_contents_1)
-  in
+  let* commitment_1 = split_slot dal_node slot_contents_1 in
   let slot_contents_2 = " 400 " in
-  let* commitment_2 =
-    RPC.call dal_node (Rollup.Dal.RPC.split_slot slot_contents_2)
-  in
+  let* commitment_2 = split_slot dal_node slot_contents_2 in
   (* 2. Run rollup node for an originated rollup. *)
   let* genesis_info =
     RPC.Client.call ~hooks client