diff --git a/src/lib_shell_services/validation_errors.mli b/src/lib_shell_services/validation_errors.mli
new file mode 100644
index 000000000..f1e0a3254
--- /dev/null
+++ b/src/lib_shell_services/validation_errors.mli
@@ -0,0 +1,47 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright (c) 2014 - 2018.                                          *)
+(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
+(*                                                                        *)
+(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
+(*                                                                        *)
+(**************************************************************************)
+
+(***************** Prevalidation errors ***********************************)
+
+type error += Parse_error
+type error += Too_many_operations
+type error += Oversized_operation of { size: int ; max: int }
+type error += Future_block_header of Block_hash.t
+
+(************************* State errors ***********************************)
+
+type error +=  Unknown_chain of Chain_id.t
+type error += Bad_data_dir
+type error += Block_not_invalid of Block_hash.t
+
+(* Block database error *)
+
+type error += Inconsistent_hash of Context_hash.t * Context_hash.t
+
+(******************* Bootstrap pipeline errors ****************************)
+
+type error += Invalid_locator of P2p_peer.Id.t * Block_locator.t
+
+(******************* Protocol validator errors ****************************)
+
+type protocol_error =
+  | Compilation_failed
+  | Dynlinking_failed
+
+type error += Invalid_protocol of { hash: Protocol_hash.t ; error: protocol_error }
+
+(********************* Peer validator errors ******************************)
+
+type error +=
+  | Unknown_ancestor
+  | Known_invalid
+
+(************************ Validator errors ********************************)
+
+type error +=  Inactive_chain of Chain_id.t