diff --git a/src/bin_evm_proxy/lib_dev/simulation.ml b/src/bin_evm_proxy/lib_dev/simulation.ml
index 38bff242fd700b421fbd93a1e96749454999ac0c..4208c8308bea0f1c5a6a31a6692be8e35f864ceb 100644
--- a/src/bin_evm_proxy/lib_dev/simulation.ml
+++ b/src/bin_evm_proxy/lib_dev/simulation.ml
@@ -88,9 +88,18 @@ let new_chunked_tag = "\002"
 (** Tag signaling a simulation message containing a chunk *)
 let chunk_tag = "\003"
 
+(** Tag indicating simulation is an evaluation *)
+let evaluation_tag = "\000"
+
+(** Tag indicating simulation is a validation *)
+let validation_tag = "\001"
+
 (** [hex_str_of_binary_string s] translate a binary string into an hax string *)
 let hex_str_of_binary_string s = s |> Hex.of_string |> Hex.show
 
+(** [add_tag tag bytes] prefixes bytes by the given tag *)
+let add_tag tag bytes = tag ^ Bytes.to_string bytes |> String.to_bytes
+
 let encode_message = function
   | Start -> hex_str_of_binary_string @@ simulation_tag
   | Simple s -> hex_str_of_binary_string @@ simulation_tag ^ simple_tag ^ s
@@ -103,12 +112,16 @@ let encode_message = function
 
 let encode call =
   let open Result_syntax in
-  let* messages = call |> rlp_encode |> split_in_messages in
+  let* messages =
+    call |> rlp_encode |> add_tag evaluation_tag |> split_in_messages
+  in
   return @@ List.map encode_message messages
 
 let encode_tx tx =
   let open Result_syntax in
-  let* messages = tx |> tx_rlp_encode |> split_in_messages in
+  let* messages =
+    tx |> tx_rlp_encode |> add_tag validation_tag |> split_in_messages
+  in
   return @@ List.map encode_message messages
 
 module Encodings = struct
diff --git a/src/kernel_evm/kernel/src/simulation.rs b/src/kernel_evm/kernel/src/simulation.rs
index 5b8d74f38810bc3609a2b6e018817cbf18c26c1e..fadfe3dcaedb4715f1b42ead1de988b33a38ff3d 100644
--- a/src/kernel_evm/kernel/src/simulation.rs
+++ b/src/kernel_evm/kernel/src/simulation.rs
@@ -29,6 +29,10 @@ pub const SIMULATION_CHUNK_TAG: u8 = 3;
 /// Maximum gas used by the evaluation. Bounded to limit DOS on the rollup node
 /// Is used as default value if no gas is set.
 pub const MAX_EVALUATION_GAS: u64 = 1_000_000_000u64;
+/// Tag indicating simulation is an evaluation.
+pub const EVALUATION_TAG: u8 = 0x00;
+/// Tag indicating simulation is a validation.
+pub const VALIDATION_TAG: u8 = 0x01;
 
 /// Container for eth_call data, used in messages sent by the rollup node
 /// simulation.
@@ -214,15 +218,14 @@ impl TryFrom<&[u8]> for Message {
     type Error = DecoderError;
 
     fn try_from(bytes: &[u8]) -> Result<Self, Self::Error> {
-        if let Ok(simulation) = Evaluation::try_from(bytes) {
-            return Ok(Message::Evaluation(simulation));
-        }
+        let Some(&tag) = bytes.first() else {return Err(DecoderError::Custom("Empty simulation message"))};
+        let Some(bytes) = bytes.get(1..) else {return Err(DecoderError::Custom("Empty simulation message"))};
 
-        if let Ok(tx_validation) = TxValidation::try_from(bytes) {
-            return Ok(Message::TxValidation(tx_validation));
+        match tag {
+            EVALUATION_TAG => Evaluation::try_from(bytes).map(Message::Evaluation),
+            VALIDATION_TAG => TxValidation::try_from(bytes).map(Message::TxValidation),
+            _ => Err(DecoderError::Custom("Unknown message to simulate")),
         }
-
-        Err(DecoderError::Custom("Unknown message to simulate"))
     }
 }
 
@@ -574,7 +577,11 @@ mod tests {
 
         let mut encoded =
             hex::decode("f84894242424242424242424242424242424242424242494353535353535353535353535353535353535353588672b00000000000088ce56000000000000883582000000000000821616").unwrap();
-        let mut input = vec![parsing::SIMULATION_TAG, SIMULATION_SIMPLE_TAG];
+        let mut input = vec![
+            parsing::SIMULATION_TAG,
+            SIMULATION_SIMPLE_TAG,
+            EVALUATION_TAG,
+        ];
         input.append(&mut encoded);
 
         let parsed = Input::parse(&input);
@@ -605,7 +612,7 @@ mod tests {
         };
 
         let encoded = hex::decode(
-            "ff01e68094907823e0a92f94355968feb2cbf0fbb594fe321488672b0000000000008080846d4ce63c",
+            "ff0100e68094907823e0a92f94355968feb2cbf0fbb594fe321488672b0000000000008080846d4ce63c",
         )
         .unwrap();
 
@@ -700,7 +707,11 @@ mod tests {
         assert_eq!(tx, expected);
 
         let mut encoded = hex::decode(hex).unwrap();
-        let mut input = vec![parsing::SIMULATION_TAG, SIMULATION_SIMPLE_TAG];
+        let mut input = vec![
+            parsing::SIMULATION_TAG,
+            SIMULATION_SIMPLE_TAG,
+            VALIDATION_TAG,
+        ];
         input.append(&mut encoded);
 
         let parsed = Input::parse(&input);
diff --git a/tezt/tests/evm_rollup.ml b/tezt/tests/evm_rollup.ml
index 42a2a13d0f543425ee9f4aa6053f4926830d64f8..d371a818d20cbb4a6a51077bd59f0c724fc0ae5d 100644
--- a/tezt/tests/evm_rollup.ml
+++ b/tezt/tests/evm_rollup.ml
@@ -1594,7 +1594,7 @@ let test_eth_call_storage_contract_proxy =
             Hex.to_string @@ `Hex "ff";
             Hex.to_string
             @@ `Hex
-                 "ff01e68094d77420f73b4612a7a99dba8c2afd30a1886b03448857040000000000008080844e70b1dc";
+                 "ff0100e68094d77420f73b4612a7a99dba8c2afd30a1886b03448857040000000000008080844e70b1dc";
           ]
       in
       let expected_insights =