diff --git a/.gitlab/ci/jobs/packaging/opam_package.yml b/.gitlab/ci/jobs/packaging/opam_package.yml
index d5e69c9f1915b348e46189b31932bbc7857b2751..c41066e99346f1aa113fe979d2a5d2e1c57248f5 100644
--- a/.gitlab/ci/jobs/packaging/opam_package.yml
+++ b/.gitlab/ci/jobs/packaging/opam_package.yml
@@ -330,7 +330,7 @@ opam:octez-node:
 opam:octez-node-config:
   extends:
     - .opam_template
-    - .rules_template__trigger_opam_batch_2
+    - .rules_template__trigger_opam_batch_1
   variables:
     package: octez-node-config
 
@@ -372,7 +372,7 @@ opam:octez-proxy-server:
 opam:octez-signer:
   extends:
     - .opam_template
-    - .rules_template__trigger_opam_batch_2
+    - .rules_template__trigger_opam_batch_1
   variables:
     package: octez-signer
 
@@ -1243,7 +1243,7 @@ opam:tezos-protocol-plugin-007-PsDELPH1:
 opam:tezos-protocol-plugin-007-PsDELPH1-registerer:
   extends:
     - .opam_template
-    - .rules_template__trigger_opam_batch_1
+    - .rules_template__trigger_opam_batch_2
   variables:
     package: tezos-protocol-plugin-007-PsDELPH1-registerer
 
@@ -1257,7 +1257,7 @@ opam:tezos-protocol-plugin-008-PtEdo2Zk:
 opam:tezos-protocol-plugin-008-PtEdo2Zk-registerer:
   extends:
     - .opam_template
-    - .rules_template__trigger_opam_batch_1
+    - .rules_template__trigger_opam_batch_2
   variables:
     package: tezos-protocol-plugin-008-PtEdo2Zk-registerer
 
diff --git a/manifest/main.ml b/manifest/main.ml
index 6b6b8c6e8ea3b0c57390a6083b0cb30f8552fe5b..ed7399d711d48459ff426914ad42c65021796588 100644
--- a/manifest/main.ml
+++ b/manifest/main.ml
@@ -5462,7 +5462,7 @@ let hash = Protocol.hash
             |> open_ ~m:"TzPervasives.Error_monad.Legacy_monad_globals";
             embedded |> open_;
             plugin |> open_;
-            octez_shell |> open_;
+            octez_validation |> open_;
           ]
         ~modules:["Plugin_registerer"]
         ~bisect_ppx:(if N.(number >= 008) then Yes else No)
diff --git a/opam/tezos-protocol-plugin-007-PsDELPH1-registerer.opam b/opam/tezos-protocol-plugin-007-PsDELPH1-registerer.opam
index bc9f4679581ea9cf1fee82daacb3953abf112b09..3db26c389b376841281ee3c54d51a263faea49c1 100644
--- a/opam/tezos-protocol-plugin-007-PsDELPH1-registerer.opam
+++ b/opam/tezos-protocol-plugin-007-PsDELPH1-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-007-PsDELPH1"
   "tezos-protocol-plugin-007-PsDELPH1"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-008-PtEdo2Zk-registerer.opam b/opam/tezos-protocol-plugin-008-PtEdo2Zk-registerer.opam
index 7ee87971a122c8b9cfd26f7da6e3087fdf0b0b0a..56d6cc757e1f8fd32f3aa55f7124eedccf09d2ec 100644
--- a/opam/tezos-protocol-plugin-008-PtEdo2Zk-registerer.opam
+++ b/opam/tezos-protocol-plugin-008-PtEdo2Zk-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-008-PtEdo2Zk"
   "tezos-protocol-plugin-008-PtEdo2Zk"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-009-PsFLoren-registerer.opam b/opam/tezos-protocol-plugin-009-PsFLoren-registerer.opam
index a1e464f3b37d305f763b0e5ad9d75d63fa698ff7..eb059b7dff693d49c11e0b526b2565069b6c4172 100644
--- a/opam/tezos-protocol-plugin-009-PsFLoren-registerer.opam
+++ b/opam/tezos-protocol-plugin-009-PsFLoren-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-009-PsFLoren"
   "tezos-protocol-plugin-009-PsFLoren"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-010-PtGRANAD-registerer.opam b/opam/tezos-protocol-plugin-010-PtGRANAD-registerer.opam
index e645a364d57730debe4f2c5f9a1bf59f19e81404..448ee8d758b4c60b21a0bd5f870372aa8958b967 100644
--- a/opam/tezos-protocol-plugin-010-PtGRANAD-registerer.opam
+++ b/opam/tezos-protocol-plugin-010-PtGRANAD-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-010-PtGRANAD"
   "tezos-protocol-plugin-010-PtGRANAD"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-011-PtHangz2-registerer.opam b/opam/tezos-protocol-plugin-011-PtHangz2-registerer.opam
index f85f268c8aa7c0f3838c640e2aac8f6712951c4b..a8896327ff3ddc69cee864cbd95acaf11fbb4374 100644
--- a/opam/tezos-protocol-plugin-011-PtHangz2-registerer.opam
+++ b/opam/tezos-protocol-plugin-011-PtHangz2-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-011-PtHangz2"
   "tezos-protocol-plugin-011-PtHangz2"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-012-Psithaca-registerer.opam b/opam/tezos-protocol-plugin-012-Psithaca-registerer.opam
index 6ec7e8eeb7a6cdc841151137e590d95532c1097c..99b07167a8e8eea560bdc2459ac050118cd03808 100644
--- a/opam/tezos-protocol-plugin-012-Psithaca-registerer.opam
+++ b/opam/tezos-protocol-plugin-012-Psithaca-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-012-Psithaca"
   "tezos-protocol-plugin-012-Psithaca"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-013-PtJakart-registerer.opam b/opam/tezos-protocol-plugin-013-PtJakart-registerer.opam
index 3f540cad2b628afba1c1827fa5eb9a0486ca261e..d6934156087185c5cc0003d65a6038b147d25271 100644
--- a/opam/tezos-protocol-plugin-013-PtJakart-registerer.opam
+++ b/opam/tezos-protocol-plugin-013-PtJakart-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-013-PtJakart"
   "tezos-protocol-plugin-013-PtJakart"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-014-PtKathma-registerer.opam b/opam/tezos-protocol-plugin-014-PtKathma-registerer.opam
index 831c43727c934c3d0cafceb4ea8b7b7ad8005d3b..f50f6777c1e2d8b36f4b7c19eedc411318b83868 100644
--- a/opam/tezos-protocol-plugin-014-PtKathma-registerer.opam
+++ b/opam/tezos-protocol-plugin-014-PtKathma-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-014-PtKathma"
   "tezos-protocol-plugin-014-PtKathma"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-015-PtLimaPt-registerer.opam b/opam/tezos-protocol-plugin-015-PtLimaPt-registerer.opam
index 69d259bf47d5edf4477768b4bd8bbb7905997867..76a740446982adef48ab06e65302a65360a38978 100644
--- a/opam/tezos-protocol-plugin-015-PtLimaPt-registerer.opam
+++ b/opam/tezos-protocol-plugin-015-PtLimaPt-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-015-PtLimaPt"
   "tezos-protocol-plugin-015-PtLimaPt"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-016-PtMumbai-registerer.opam b/opam/tezos-protocol-plugin-016-PtMumbai-registerer.opam
index f283e4ac00cb73cf45a98976f7754ecc1a681803..153bc723130d2333a885243645fa4e7350fde57d 100644
--- a/opam/tezos-protocol-plugin-016-PtMumbai-registerer.opam
+++ b/opam/tezos-protocol-plugin-016-PtMumbai-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-016-PtMumbai"
   "tezos-protocol-plugin-016-PtMumbai"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-017-PtNairob-registerer.opam b/opam/tezos-protocol-plugin-017-PtNairob-registerer.opam
index f11ab3a39974fbd2a2159eade6da2b3295daf246..9e53f2562cb4ebc0a909ff5a54343e90d59032fe 100644
--- a/opam/tezos-protocol-plugin-017-PtNairob-registerer.opam
+++ b/opam/tezos-protocol-plugin-017-PtNairob-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-017-PtNairob"
   "tezos-protocol-plugin-017-PtNairob"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/opam/tezos-protocol-plugin-alpha-registerer.opam b/opam/tezos-protocol-plugin-alpha-registerer.opam
index ec51b5b1d9c6ac52f7d2d8a684c4230a9bac97dd..a70e9508f966373a4c961dbaacbd9cc0411b7dd3 100644
--- a/opam/tezos-protocol-plugin-alpha-registerer.opam
+++ b/opam/tezos-protocol-plugin-alpha-registerer.opam
@@ -13,7 +13,7 @@ depends: [
   "tezos-base"
   "tezos-embedded-protocol-alpha"
   "tezos-protocol-plugin-alpha"
-  "tezos-shell"
+  "tezos-validation"
 ]
 build: [
   ["rm" "-r" "vendors"]
diff --git a/src/lib_shell/chain_validator.ml b/src/lib_shell/chain_validator.ml
index 0c179031bbb63cb841853a6e62b2d5a8262da2f4..588fe1ef44e2f6a190048743e7c7658b38edc5a8 100644
--- a/src/lib_shell/chain_validator.ml
+++ b/src/lib_shell/chain_validator.ml
@@ -364,24 +364,6 @@ let broadcast_head w ~previous block =
       Lwt.return_unit)
     else Distributed_db.Advertise.current_branch nv.chain_db
 
-let safe_get_prevalidator_filter hash =
-  let open Lwt_syntax in
-  match Shell_plugin.find_filter hash with
-  | Some filter -> return_ok filter
-  | None -> (
-      match Registered_protocol.get hash with
-      | None ->
-          (* FIXME. *)
-          (* This should not happen: it should be handled in the validator. *)
-          failwith
-            "chain_validator: missing protocol '%a' for the current block."
-            Protocol_hash.pp_short
-            hash
-      | Some (module Proto : Registered_protocol.T) ->
-          let* () = Events.(emit prevalidator_filter_not_found) hash in
-          return_ok
-            (module Shell_plugin.No_filter (Proto) : Shell_plugin.FILTER))
-
 let instantiate_prevalidator parameters set_prevalidator block chain_db =
   let open Lwt_syntax in
   let* r =
@@ -389,7 +371,9 @@ let instantiate_prevalidator parameters set_prevalidator block chain_db =
     let* new_protocol =
       Store.Block.protocol_hash parameters.chain_store block
     in
-    let* filter = safe_get_prevalidator_filter new_protocol in
+    let* filter =
+      Shell_plugin.find_filter ~block_hash:(Store.Block.hash block) new_protocol
+    in
     Prevalidator.create parameters.prevalidator_limits filter chain_db
   in
   match r with
diff --git a/src/lib_shell/prevalidation.ml b/src/lib_shell/prevalidation.ml
index 3dd8940456e0c2081e51e8dcd5597a4109b1e7ba..2067a3bed8e1d4f00f9c7aa16420d145f18670cc 100644
--- a/src/lib_shell/prevalidation.ml
+++ b/src/lib_shell/prevalidation.ml
@@ -166,10 +166,17 @@ module MakeAbstract (Chain_store : CHAIN_STORE) (Filter : Shell_plugin.FILTER) :
     return {validation_info; mempool; filter_state}
 
   let pre_filter state filter_config op =
-    Filter.Mempool.pre_filter
-      ~filter_state:state.filter_state
-      filter_config
-      op.protocol
+    match Filter.Mempool.syntactic_check op.protocol with
+    | `Ill_formed ->
+        Lwt.return
+          (`Refused
+            (Error_monad.TzTrace.make
+               (Error_monad.error_of_fmt "Ill-formed operation filtered")))
+    | `Well_formed ->
+        Filter.Mempool.pre_filter
+          ~filter_state:state.filter_state
+          filter_config
+          op.protocol
 
   type error_classification = Prevalidator_classification.error_classification
 
diff --git a/src/lib_shell/test/test_prevalidation.ml b/src/lib_shell/test/test_prevalidation.ml
index 954b210c28588863dea70b9f518bff401fd89b01..946d8fdf34e52784044ce98b269f2bf06eb81488 100644
--- a/src/lib_shell/test/test_prevalidation.ml
+++ b/src/lib_shell/test/test_prevalidation.ml
@@ -495,6 +495,8 @@ module Toy_filter = struct
       | F_crash -> assert false
 
     let conflict_handler _ ~existing_operation:_ ~new_operation:_ = assert false
+
+    let syntactic_check _ = `Well_formed
   end
 end
 
diff --git a/src/lib_validation/block_validation.ml b/src/lib_validation/block_validation.ml
index a56a1f850497b365e392a8daf82d4387c5fc7699..212456eae3d9249800726ed41dc180a794e1d377 100644
--- a/src/lib_validation/block_validation.ml
+++ b/src/lib_validation/block_validation.ml
@@ -289,7 +289,9 @@ let may_patch_protocol ~user_activated_upgrades
       in
       return {validation_result with context}
 
-module Make (Proto : Registered_protocol.T) = struct
+module Make (Filter : Shell_plugin.FILTER) = struct
+  module Proto = Filter.Proto
+
   type 'operation_data preapplied_operation = {
     hash : Operation_hash.t;
     raw : Operation.t;
@@ -870,7 +872,10 @@ module Make (Proto : Registered_protocol.T) = struct
             in
             let open Lwt_result_syntax in
             let* validation_state =
-              Proto.validate_operation pv.validation_state op.hash operation
+              match Filter.Mempool.syntactic_check operation with
+              | `Ill_formed -> failwith "Ill-formed operation filtered"
+              | `Well_formed ->
+                  Proto.validate_operation pv.validation_state op.hash operation
             in
             let* application_state, receipt =
               Proto.apply_operation pv.application_state op.hash operation
@@ -1241,13 +1246,17 @@ module Make (Proto : Registered_protocol.T) = struct
         ~predecessor:predecessor_block_header.shell
         ~cache
     in
+
     let* state =
       List.fold_left_es
         (fun state ops ->
           List.fold_left_es
             (fun state (oph, op) ->
-              let* state = Proto.validate_operation state oph op in
-              return state)
+              match Filter.Mempool.syntactic_check op with
+              | `Ill_formed -> failwith "Ill-formed operation filtered"
+              | `Well_formed ->
+                  let* state = Proto.validate_operation state oph op in
+                  return state)
             state
             ops)
         state
@@ -1336,15 +1345,10 @@ let recompute_metadata chain_id ~predecessor_block_header ~predecessor_context
     block_hash block_header operations =
   let open Lwt_result_syntax in
   let*! pred_protocol_hash = Context_ops.get_protocol predecessor_context in
-  let* (module Proto) =
-    match Registered_protocol.get pred_protocol_hash with
-    | None ->
-        tzfail
-          (Unavailable_protocol
-             {block = block_hash; protocol = pred_protocol_hash})
-    | Some p -> return p
+  let* (module Filter) =
+    Shell_plugin.find_filter ~block_hash pred_protocol_hash
   in
-  let module Block_validation = Make (Proto) in
+  let module Block_validation = Make (Filter) in
   Block_validation.recompute_metadata
     chain_id
     ~predecessor_block_header
@@ -1383,15 +1387,10 @@ let precheck ~chain_id ~predecessor_block_header ~predecessor_block_hash
   let open Lwt_result_syntax in
   let block_hash = Block_header.hash block_header in
   let*! pred_protocol_hash = Context_ops.get_protocol predecessor_context in
-  let* (module Proto) =
-    match Registered_protocol.get pred_protocol_hash with
-    | None ->
-        tzfail
-          (Unavailable_protocol
-             {block = block_hash; protocol = pred_protocol_hash})
-    | Some p -> return p
+  let* (module Filter) =
+    Shell_plugin.find_filter ~block_hash pred_protocol_hash
   in
-  let module Block_validation = Make (Proto) in
+  let module Block_validation = Make (Filter) in
   Block_validation.precheck
     chain_id
     ~predecessor_block_header
@@ -1417,16 +1416,12 @@ let apply ?simulate ?cached_result ?(should_precheck = true)
     } ~cache block_hash block_header operations =
   let open Lwt_result_syntax in
   let*! pred_protocol_hash = Context_ops.get_protocol predecessor_context in
-  let* (module Proto) =
-    match Registered_protocol.get pred_protocol_hash with
-    | None ->
-        tzfail
-          (Unavailable_protocol
-             {block = block_hash; protocol = pred_protocol_hash})
-    | Some p -> return p
+  let* (module Filter) =
+    Shell_plugin.find_filter ~block_hash pred_protocol_hash
   in
   let* () =
-    if should_precheck && Proto.(compare environment_version V7 >= 0) then
+    if should_precheck && Filter.Proto.(compare environment_version V7 >= 0)
+    then
       precheck
         ~chain_id
         ~predecessor_block_header
@@ -1438,7 +1433,7 @@ let apply ?simulate ?cached_result ?(should_precheck = true)
         operations
     else return_unit
   in
-  let module Block_validation = Make (Proto) in
+  let module Block_validation = Make (Filter) in
   Block_validation.apply
     ?simulate
     ?cached_result
@@ -1505,24 +1500,16 @@ let preapply ~chain_id ~user_activated_upgrades
     ~predecessor_block_metadata_hash ~predecessor_ops_metadata_hash operations =
   let open Lwt_result_syntax in
   let*! protocol = Context_ops.get_protocol predecessor_context in
-  let* (module Proto) =
-    match Registered_protocol.get protocol with
-    | None ->
-        (* FIXME: https://gitlab.com/tezos/tezos/-/issues/1718 *)
-        (* This should not happen: it should be handled in the validator. *)
-        failwith
-          "Prevalidation: missing protocol '%a' for the current block."
-          Protocol_hash.pp_short
-          protocol
-    | Some protocol -> return protocol
+  let* (module Filter) =
+    Shell_plugin.find_filter ~block_hash:predecessor_hash protocol
   in
   (* The cache might be inconsistent with the context. By forcing the
      reloading of the cache, we restore the consistency. *)
-  let module Block_validation = Make (Proto) in
+  let module Block_validation = Make (Filter) in
   let* protocol_data =
     match
       Data_encoding.Binary.of_bytes_opt
-        Proto.block_header_data_encoding
+        Filter.Proto.block_header_data_encoding
         protocol_data
     with
     | None -> failwith "Invalid block header"
diff --git a/src/lib_shell/shell_plugin.ml b/src/lib_validation/shell_plugin.ml
similarity index 75%
rename from src/lib_shell/shell_plugin.ml
rename to src/lib_validation/shell_plugin.ml
index 6d1ca2a3d4f554f183538ead7a85692899cd4ccc..fd15fcc8318943500bea96b00c372bf470ab048e 100644
--- a/src/lib_shell/shell_plugin.ml
+++ b/src/lib_validation/shell_plugin.ml
@@ -46,12 +46,17 @@ module type FILTER = sig
 
     val remove : filter_state:state -> Operation_hash.t -> state
 
+    val syntactic_check : Proto.operation -> [`Well_formed | `Ill_formed]
+
     val pre_filter :
       config ->
       filter_state:state ->
       Proto.operation ->
-      [ `Passed_prefilter of Prevalidator_pending_operations.priority
-      | Prevalidator_classification.error_classification ]
+      [ `Passed_prefilter of [`High | `Medium | `Low of Q.t list]
+      | `Branch_delayed of tztrace
+      | `Branch_refused of tztrace
+      | `Refused of tztrace
+      | `Outdated of tztrace ]
       Lwt.t
 
     val add_operation_and_enforce_mempool_bound :
@@ -62,9 +67,15 @@ module type FILTER = sig
       ( state
         * [ `No_replace
           | `Replace of
-            Operation_hash.t * Prevalidator_classification.error_classification
-          ],
-        Prevalidator_classification.error_classification )
+            Operation_hash.t
+            * [ `Branch_delayed of tztrace
+              | `Branch_refused of tztrace
+              | `Refused of tztrace
+              | `Outdated of tztrace ] ],
+        [ `Branch_delayed of tztrace
+        | `Branch_refused of tztrace
+        | `Refused of tztrace
+        | `Outdated of tztrace ] )
       result
       Lwt.t
 
@@ -98,6 +109,8 @@ module No_filter (Proto : Registered_protocol.T) :
 
     let flush _ ~head:_ = Lwt_result_syntax.return_unit
 
+    let syntactic_check _ = `Well_formed
+
     let pre_filter _ ~filter_state:_ _ =
       Lwt.return @@ `Passed_prefilter (`Low [])
 
@@ -166,4 +179,34 @@ let add_to_filter_table proto_hash filter =
 let register_filter (module Filter : FILTER) =
   add_to_filter_table Filter.Proto.hash (module Filter)
 
-let find_filter = Protocol_hash.Table.find filter_table
+let validator_filter_not_found =
+  Internal_event.Simple.declare_1
+    ~section:["block"; "validation"]
+    ~name:"protocol_filter_not_found"
+    ~msg:"no protocol filter found for protocol {protocol_hash}"
+    ~level:Warning
+    ~pp1:Protocol_hash.pp
+    ("protocol_hash", Protocol_hash.encoding)
+
+let find_filter ~block_hash protocol_hash =
+  let open Lwt_result_syntax in
+  match Protocol_hash.Table.find filter_table protocol_hash with
+  | Some filter -> return filter
+  | None -> (
+      match Registered_protocol.get protocol_hash with
+      | None ->
+          tzfail
+            (Block_validator_errors.Unavailable_protocol
+               {block = block_hash; protocol = protocol_hash})
+      | Some (module Proto : Registered_protocol.T) ->
+          let*! () =
+            match Proto.environment_version with
+            | V0 ->
+                (* This is normal for protocols Genesis and 000
+                   because they don't have a plugin. *)
+                Lwt.return_unit
+            | _ ->
+                Internal_event.Simple.(emit validator_filter_not_found)
+                  protocol_hash
+          in
+          return (module No_filter (Proto) : FILTER))
diff --git a/src/lib_shell/shell_plugin.mli b/src/lib_validation/shell_plugin.mli
similarity index 86%
rename from src/lib_shell/shell_plugin.mli
rename to src/lib_validation/shell_plugin.mli
index befd3f7faf35a5f9e08b55b7d5e763a0a58b670e..6ae50306d179d35f0748250a3ca7d38eab3d8887 100644
--- a/src/lib_shell/shell_plugin.mli
+++ b/src/lib_validation/shell_plugin.mli
@@ -58,6 +58,14 @@ module type FILTER = sig
         [oph] from the state of the filter *)
     val remove : filter_state:state -> Operation_hash.t -> state
 
+    (** Perform some syntactic checks on the operation.
+
+        To be used mostly as an exceptional mechanism to prevent
+        ill-formed operations to block block application.
+
+        Should be called before the {!pre_filter}, does not need a context. *)
+    val syntactic_check : Proto.operation -> [`Well_formed | `Ill_formed]
+
     (** [pre_filter config ~filter_state operation_data]
         is called on arrival of an operation and after a flush of
         the prevalidator. This function calls the [pre_filter] in the protocol
@@ -73,8 +81,11 @@ module type FILTER = sig
       config ->
       filter_state:state ->
       Proto.operation ->
-      [ `Passed_prefilter of Prevalidator_pending_operations.priority
-      | Prevalidator_classification.error_classification ]
+      [ `Passed_prefilter of [`High | `Medium | `Low of Q.t list]
+      | `Branch_delayed of tztrace
+      | `Branch_refused of tztrace
+      | `Refused of tztrace
+      | `Outdated of tztrace ]
       Lwt.t
 
     (** Add an operation to the filter {!state}.
@@ -104,9 +115,15 @@ module type FILTER = sig
       ( state
         * [ `No_replace
           | `Replace of
-            Operation_hash.t * Prevalidator_classification.error_classification
-          ],
-        Prevalidator_classification.error_classification )
+            Operation_hash.t
+            * [ `Branch_delayed of tztrace
+              | `Branch_refused of tztrace
+              | `Refused of tztrace
+              | `Outdated of tztrace ] ],
+        [ `Branch_delayed of tztrace
+        | `Branch_refused of tztrace
+        | `Refused of tztrace
+        | `Outdated of tztrace ] )
       result
       Lwt.t
 
@@ -159,8 +176,10 @@ val register_rpc : (module RPC) -> unit
 (** Register a metrics plugin module *)
 val register_metrics : (module METRICS) -> unit
 
-(** Looks for a mempool filter plug-in for a specific protocol. *)
-val find_filter : Protocol_hash.t -> (module FILTER) option
+(** Looks for a protocol filter plug-in for a specific protocol. The
+    [block_hash] argument is used for the error message. *)
+val find_filter :
+  block_hash:Block_hash.t -> Protocol_hash.t -> (module FILTER) tzresult Lwt.t
 
 (** Looks for an rpc plug-in for a specific protocol. *)
 val find_rpc : Protocol_hash.t -> (module RPC) option
diff --git a/src/proto_007_PsDELPH1/lib_plugin/dune b/src/proto_007_PsDELPH1/lib_plugin/dune
index b4f3fcd6ed5e7dc848a7b83cddc1f7e51eca9081..72b937ff6e697111b26047af068c3ccc6d59587e 100644
--- a/src/proto_007_PsDELPH1/lib_plugin/dune
+++ b/src/proto_007_PsDELPH1/lib_plugin/dune
@@ -21,12 +21,12 @@
   tezos-base
   tezos-embedded-protocol-007-PsDELPH1
   tezos-protocol-plugin-007-PsDELPH1
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_007_PsDELPH1
   -open Tezos_protocol_plugin_007_PsDELPH1
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_008_PtEdo2Zk/lib_plugin/dune b/src/proto_008_PtEdo2Zk/lib_plugin/dune
index 624c38de08ff500beaeab3a970dd3aca5d6cfd3e..fe0905f1f400411d075ea7f07d0ddb7ef36df4ff 100644
--- a/src/proto_008_PtEdo2Zk/lib_plugin/dune
+++ b/src/proto_008_PtEdo2Zk/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-008-PtEdo2Zk
   tezos-protocol-plugin-008-PtEdo2Zk
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_008_PtEdo2Zk
   -open Tezos_protocol_plugin_008_PtEdo2Zk
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_009_PsFLoren/lib_plugin/dune b/src/proto_009_PsFLoren/lib_plugin/dune
index 2e834249870384b437f9e939a57098ee3f024cdf..88c97a269bbd70d0dba8227ee6fec09ef54eb886 100644
--- a/src/proto_009_PsFLoren/lib_plugin/dune
+++ b/src/proto_009_PsFLoren/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-009-PsFLoren
   tezos-protocol-plugin-009-PsFLoren
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_009_PsFLoren
   -open Tezos_protocol_plugin_009_PsFLoren
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_010_PtGRANAD/lib_plugin/dune b/src/proto_010_PtGRANAD/lib_plugin/dune
index a249bc0db86f45356a56af0938aa6eb739c76cfb..0c21a73736e0e3806cf8a3869248189e35aa8747 100644
--- a/src/proto_010_PtGRANAD/lib_plugin/dune
+++ b/src/proto_010_PtGRANAD/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-010-PtGRANAD
   tezos-protocol-plugin-010-PtGRANAD
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_010_PtGRANAD
   -open Tezos_protocol_plugin_010_PtGRANAD
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_011_PtHangz2/lib_plugin/dune b/src/proto_011_PtHangz2/lib_plugin/dune
index f5838c36abc3df305b3e6fc96c687a2ea3256b25..be7b099664655ec45077442e20e37a36f9750b1d 100644
--- a/src/proto_011_PtHangz2/lib_plugin/dune
+++ b/src/proto_011_PtHangz2/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-011-PtHangz2
   tezos-protocol-plugin-011-PtHangz2
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_011_PtHangz2
   -open Tezos_protocol_plugin_011_PtHangz2
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_012_Psithaca/lib_plugin/dune b/src/proto_012_Psithaca/lib_plugin/dune
index edb66c2d20a2a8a0c2a5fc83237ebd427df34e38..4e11c0bb314347e9c5e37e0532cfc76e2c9b7724 100644
--- a/src/proto_012_Psithaca/lib_plugin/dune
+++ b/src/proto_012_Psithaca/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-012-Psithaca
   tezos-protocol-plugin-012-Psithaca
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_012_Psithaca
   -open Tezos_protocol_plugin_012_Psithaca
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_013_PtJakart/lib_plugin/dune b/src/proto_013_PtJakart/lib_plugin/dune
index 8afa4d74c043ed7285be0d101ef67b2d0a4bc532..0a306d1209466a738e424335964bb81cd5abf071 100644
--- a/src/proto_013_PtJakart/lib_plugin/dune
+++ b/src/proto_013_PtJakart/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-013-PtJakart
   tezos-protocol-plugin-013-PtJakart
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_013_PtJakart
   -open Tezos_protocol_plugin_013_PtJakart
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_014_PtKathma/lib_plugin/dune b/src/proto_014_PtKathma/lib_plugin/dune
index ad8aba89065067b7aa65260dc778fb31d84560fe..ff1a881658a474a5ba11d295875add0b4388223d 100644
--- a/src/proto_014_PtKathma/lib_plugin/dune
+++ b/src/proto_014_PtKathma/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-014-PtKathma
   tezos-protocol-plugin-014-PtKathma
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_014_PtKathma
   -open Tezos_protocol_plugin_014_PtKathma
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_015_PtLimaPt/lib_plugin/dune b/src/proto_015_PtLimaPt/lib_plugin/dune
index 6d1fe04877654098347f619fc0aa7696aac4c0d4..baa723a3b681dfd253bada2f02d1bd111356e976 100644
--- a/src/proto_015_PtLimaPt/lib_plugin/dune
+++ b/src/proto_015_PtLimaPt/lib_plugin/dune
@@ -23,12 +23,12 @@
   tezos-base
   tezos-embedded-protocol-015-PtLimaPt
   tezos-protocol-plugin-015-PtLimaPt
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_015_PtLimaPt
   -open Tezos_protocol_plugin_015_PtLimaPt
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_016_PtMumbai/lib_plugin/dune b/src/proto_016_PtMumbai/lib_plugin/dune
index 4b63789b72b73579e16bd4d06c17a323ca19437e..7021bb912e5096b48a157e6d1cdf4d8df7399d8d 100644
--- a/src/proto_016_PtMumbai/lib_plugin/dune
+++ b/src/proto_016_PtMumbai/lib_plugin/dune
@@ -25,12 +25,12 @@
   tezos-base
   tezos-embedded-protocol-016-PtMumbai
   tezos-protocol-plugin-016-PtMumbai
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_016_PtMumbai
   -open Tezos_protocol_plugin_016_PtMumbai
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_016_PtMumbai/lib_plugin/mempool.ml b/src/proto_016_PtMumbai/lib_plugin/mempool.ml
index bdec72bfb9389890b39273f9046c351029107f38..a641e48b105222ac119b387657876bad22d1664a 100644
--- a/src/proto_016_PtMumbai/lib_plugin/mempool.ml
+++ b/src/proto_016_PtMumbai/lib_plugin/mempool.ml
@@ -774,6 +774,8 @@ let pre_filter_far_future_consensus_ops config ~filter_state
   in
   match res with Ok b -> Lwt.return b | Error _ -> Lwt.return_false
 
+let syntactic_check _ = `Well_formed
+
 (** A quasi infinite amount of "valid" (pre)endorsements could be
       sent by a committee member, one for each possible round number.
 
diff --git a/src/proto_017_PtNairob/lib_plugin/dune b/src/proto_017_PtNairob/lib_plugin/dune
index 2c59eac8e4ed9a6966579ea08a7239a8a14483a1..250c70cf1842f229dc2274d51e2479c6ac5f665b 100644
--- a/src/proto_017_PtNairob/lib_plugin/dune
+++ b/src/proto_017_PtNairob/lib_plugin/dune
@@ -25,12 +25,12 @@
   tezos-base
   tezos-embedded-protocol-017-PtNairob
   tezos-protocol-plugin-017-PtNairob
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_017_PtNairob
   -open Tezos_protocol_plugin_017_PtNairob
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_017_PtNairob/lib_plugin/mempool.ml b/src/proto_017_PtNairob/lib_plugin/mempool.ml
index bdec72bfb9389890b39273f9046c351029107f38..41e1c01924d5c28b9a555b99bbf9037fe5a62b9f 100644
--- a/src/proto_017_PtNairob/lib_plugin/mempool.ml
+++ b/src/proto_017_PtNairob/lib_plugin/mempool.ml
@@ -535,6 +535,63 @@ let check_minimal_weight config state ~fee ~gas_limit op =
             (`Branch_delayed
               [Environment.wrap_tzerror (Fees_too_low_for_mempool required_fee)])
 
+let output_proof_encoding =
+  let open Data_encoding in
+  obj3
+    (req
+       "output_proof"
+       Sc_rollup_wasm.V2_0_0.Protocol_implementation.proof_encoding)
+    (req "output_proof_state" Sc_rollup.State_hash.encoding)
+    (req "output_proof_output" Variable.bytes)
+
+let kinded_hash_to_state_hash = function
+  | `Value hash | `Node hash ->
+      Sc_rollup.State_hash.context_hash_to_state_hash hash
+
+let is_invalid_op : type t. t manager_operation -> bool = function
+  | Sc_rollup_execute_outbox_message
+      {rollup = _; cemented_commitment = _; output_proof} -> (
+      match
+        Data_encoding.Binary.of_string_opt output_proof_encoding output_proof
+      with
+      | None -> true
+      | Some (output_proof, output_proof_state, _) ->
+          not
+            (Sc_rollup.State_hash.equal
+               output_proof_state
+               (kinded_hash_to_state_hash
+                  output_proof.Environment.Context.Proof.before)))
+  | _ -> false
+
+let rec contains_invalid_op : type t. t Kind.manager contents_list -> bool =
+  function
+  | Single (Manager_operation {operation; _}) -> is_invalid_op operation
+  | Cons (Manager_operation {operation; _}, rest) ->
+      is_invalid_op operation || contains_invalid_op rest
+
+let syntactic_check
+    ({shell = _; protocol_data = Operation_data {contents; _}} : Main.operation)
+    =
+  match contents with
+  | Single (Failing_noop _)
+  | Single (Preendorsement _)
+  | Single (Endorsement _)
+  | Single (Dal_attestation _)
+  | Single (Seed_nonce_revelation _)
+  | Single (Double_preendorsement_evidence _)
+  | Single (Double_endorsement_evidence _)
+  | Single (Double_baking_evidence _)
+  | Single (Activate_account _)
+  | Single (Proposals _)
+  | Single (Vdf_revelation _)
+  | Single (Drain_delegate _)
+  | Single (Ballot _) ->
+      `Well_formed
+  | Single (Manager_operation _) as op ->
+      if contains_invalid_op op then `Ill_formed else `Well_formed
+  | Cons (Manager_operation _, _) as op ->
+      if contains_invalid_op op then `Ill_formed else `Well_formed
+
 let pre_filter_manager :
     type t.
     config ->
diff --git a/src/proto_alpha/lib_plugin/dune b/src/proto_alpha/lib_plugin/dune
index d68db6e047471cf25517c61fe7b66cd7f03587a3..c0ae384ad9c5fd2d0ea68ca9086a4ae999bf26d7 100644
--- a/src/proto_alpha/lib_plugin/dune
+++ b/src/proto_alpha/lib_plugin/dune
@@ -25,12 +25,12 @@
   tezos-base
   tezos-embedded-protocol-alpha
   tezos-protocol-plugin-alpha
-  tezos-shell)
+  tezos-validation)
  (flags
   (:standard)
   -open Tezos_base.TzPervasives
   -open Tezos_base.TzPervasives.Error_monad.Legacy_monad_globals
   -open Tezos_embedded_protocol_alpha
   -open Tezos_protocol_plugin_alpha
-  -open Tezos_shell)
+  -open Tezos_validation)
  (modules Plugin_registerer))
diff --git a/src/proto_alpha/lib_plugin/mempool.ml b/src/proto_alpha/lib_plugin/mempool.ml
index 7347f2b19750986215f75b5fedc80eae09c80fcb..1199fb4161137f2f5c6638bdff4ed110f8f82929 100644
--- a/src/proto_alpha/lib_plugin/mempool.ml
+++ b/src/proto_alpha/lib_plugin/mempool.ml
@@ -1028,3 +1028,5 @@ let conflict_handler config : Mempool.conflict_handler =
     | Ok _ | Error _ -> `Keep
   else if Operation.compare existing_operation new_operation < 0 then `Replace
   else `Keep
+
+let syntactic_check _ = `Well_formed