diff --git a/source/services/shopping/mcp.openrpc.json b/source/services/shopping/mcp.openrpc.json
index 2908d8d45..979036070 100644
--- a/source/services/shopping/mcp.openrpc.json
+++ b/source/services/shopping/mcp.openrpc.json
@@ -68,6 +68,28 @@
           }
         }
       }
+    },
+    "errors": {
+      "authentication_failed": {
+        "code": -32002,
+        "message": "Authentication failed",
+        "data": { "$ref": "../../schemas/common/types/error_response.json" }
+      },
+      "invalid_params": {
+        "code": -32602,
+        "message": "Invalid params",
+        "data": { "$ref": "../../schemas/common/types/error_response.json" }
+      },
+      "not_found": {
+        "code": -32001,
+        "message": "Resource not found",
+        "data": { "$ref": "../../schemas/common/types/error_response.json" }
+      },
+      "idempotency_conflict": {
+        "code": -32003,
+        "message": "Idempotency conflict",
+        "data": { "$ref": "../../schemas/common/types/error_response.json" }
+      }
     }
   },
   "methods": [
@@ -79,18 +101,23 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "checkout",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/checkout.json"}
+          "schema": { "$ref": "../../schemas/shopping/checkout.json" }
         }
       ],
       "result": {
         "name": "checkout",
-        "schema": {"$ref": "#/components/schemas/checkout_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/checkout_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "get_checkout",
@@ -99,18 +126,25 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         }
       ],
       "result": {
         "name": "checkout",
-        "schema": {"$ref": "#/components/schemas/checkout_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/checkout_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" }
+      ]
     },
     {
       "name": "update_checkout",
@@ -119,23 +153,31 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         },
         {
           "name": "checkout",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/checkout.json"}
+          "schema": { "$ref": "../../schemas/shopping/checkout.json" }
         }
       ],
       "result": {
         "name": "checkout",
-        "schema": {"$ref": "#/components/schemas/checkout_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/checkout_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "complete_checkout",
@@ -146,26 +188,39 @@
           "required": true,
           "schema": {
             "allOf": [
-              {"$ref": "#/components/schemas/meta"},
-              {"required": ["ucp-agent", "idempotency-key"]}
+              { "$ref": "#/components/schemas/meta" },
+              {
+                "required": [
+                  "ucp-agent",
+                  "idempotency-key"
+                ]
+              }
             ]
           }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         },
         {
           "name": "checkout",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/checkout.json"}
+          "schema": { "$ref": "../../schemas/shopping/checkout.json" }
         }
       ],
       "result": {
         "name": "checkout",
-        "schema": {"$ref": "#/components/schemas/checkout_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/checkout_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "cancel_checkout",
@@ -176,21 +231,34 @@
           "required": true,
           "schema": {
             "allOf": [
-              {"$ref": "#/components/schemas/meta"},
-              {"required": ["ucp-agent", "idempotency-key"]}
+              { "$ref": "#/components/schemas/meta" },
+              {
+                "required": [
+                  "ucp-agent",
+                  "idempotency-key"
+                ]
+              }
             ]
           }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         }
       ],
       "result": {
         "name": "checkout",
-        "schema": {"$ref": "#/components/schemas/checkout_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/checkout_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "create_cart",
@@ -200,18 +268,23 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "cart",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/cart.json"}
+          "schema": { "$ref": "../../schemas/shopping/cart.json" }
         }
       ],
       "result": {
         "name": "cart",
-        "schema": {"$ref": "#/components/schemas/cart_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/cart_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "get_cart",
@@ -220,18 +293,25 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         }
       ],
       "result": {
         "name": "cart",
-        "schema": {"$ref": "#/components/schemas/cart_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/cart_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" }
+      ]
     },
     {
       "name": "update_cart",
@@ -240,23 +320,31 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         },
         {
           "name": "cart",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/cart.json"}
+          "schema": { "$ref": "../../schemas/shopping/cart.json" }
         }
       ],
       "result": {
         "name": "cart",
-        "schema": {"$ref": "#/components/schemas/cart_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/cart_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "cancel_cart",
@@ -267,21 +355,34 @@
           "required": true,
           "schema": {
             "allOf": [
-              {"$ref": "#/components/schemas/meta"},
-              {"required": ["ucp-agent", "idempotency-key"]}
+              { "$ref": "#/components/schemas/meta" },
+              {
+                "required": [
+                  "ucp-agent",
+                  "idempotency-key"
+                ]
+              }
             ]
           }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string"}
+          "schema": {
+            "type": "string"
+          }
         }
       ],
       "result": {
         "name": "cart",
-        "schema": {"$ref": "#/components/schemas/cart_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/cart_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" },
+        { "$ref": "#/components/errors/idempotency_conflict" }
+      ]
     },
     {
       "name": "search_catalog",
@@ -291,18 +392,22 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "catalog",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/catalog_search.json#/$defs/search_request"}
+          "schema": { "$ref": "../../schemas/shopping/catalog_search.json#/$defs/search_request" }
         }
       ],
       "result": {
         "name": "response",
-        "schema": {"$ref": "../../schemas/shopping/catalog_search.json#/$defs/search_response"}
-      }
+        "schema": { "$ref": "../../schemas/shopping/catalog_search.json#/$defs/search_response" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" }
+      ]
     },
     {
       "name": "lookup_catalog",
@@ -312,18 +417,22 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "catalog",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/lookup_request"}
+          "schema": { "$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/lookup_request" }
         }
       ],
       "result": {
         "name": "response",
-        "schema": {"$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/lookup_response"}
-      }
+        "schema": { "$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/lookup_response" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" }
+      ]
     },
     {
       "name": "get_order",
@@ -333,18 +442,26 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "id",
           "required": true,
-          "schema": {"type": "string", "description": "The unique identifier of the order."}
+          "schema": {
+            "type": "string",
+            "description": "The unique identifier of the order."
+          }
         }
       ],
       "result": {
         "name": "order",
-        "schema": {"$ref": "#/components/schemas/order_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/order_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" },
+        { "$ref": "#/components/errors/not_found" }
+      ]
     },
     {
       "name": "get_product",
@@ -354,18 +471,22 @@
         {
           "name": "meta",
           "required": true,
-          "schema": {"$ref": "#/components/schemas/meta"}
+          "schema": { "$ref": "#/components/schemas/meta" }
         },
         {
           "name": "catalog",
           "required": true,
-          "schema": {"$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/get_product_request"}
+          "schema": { "$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/get_product_request" }
         }
       ],
       "result": {
         "name": "response",
-        "schema": {"$ref": "#/components/schemas/catalog_get_product_result"}
-      }
+        "schema": { "$ref": "#/components/schemas/catalog_get_product_result" }
+      },
+      "errors": [
+        { "$ref": "#/components/errors/authentication_failed" },
+        { "$ref": "#/components/errors/invalid_params" }
+      ]
     }
   ]
 }
diff --git a/source/services/shopping/rest.openapi.json b/source/services/shopping/rest.openapi.json
index 4ea716214..5a2219b8b 100644
--- a/source/services/shopping/rest.openapi.json
+++ b/source/services/shopping/rest.openapi.json
@@ -92,6 +92,36 @@
                 }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -160,6 +190,26 @@
                 }
               }
             }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       },
@@ -237,6 +287,46 @@
                 }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -317,6 +407,46 @@
                 "schema": { "$ref": "#/components/schemas/checkout_response" }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -391,6 +521,36 @@
                 }
               }
             }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -436,6 +596,36 @@
                 "schema": { "$ref": "#/components/schemas/cart_response" }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -474,6 +664,26 @@
                 "schema": { "$ref": "#/components/schemas/cart_response" }
               }
             }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       },
@@ -517,6 +727,46 @@
                 "schema": { "$ref": "#/components/schemas/cart_response" }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -557,6 +807,36 @@
                 "schema": { "$ref": "#/components/schemas/cart_response" }
               }
             }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Idempotency conflict. A request with this Idempotency-Key was already processed with different parameters.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -601,6 +881,26 @@
                 "schema": { "$ref": "#/components/schemas/catalog_search_response" }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -645,6 +945,26 @@
                 "schema": { "$ref": "#/components/schemas/catalog_lookup_response" }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -683,6 +1003,26 @@
                 "schema": { "$ref": "#/components/schemas/order_response" }
               }
             }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Resource not found.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -727,6 +1067,26 @@
                 "schema": { "$ref": "#/components/schemas/catalog_get_product_response" }
               }
             }
+          },
+          "400": {
+            "description": "Request body failed validation.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Authentication failed or missing credentials.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/error_response"
+                }
+              }
+            }
           }
         }
       }
@@ -1021,6 +1381,9 @@
           { "$ref": "../../schemas/shopping/catalog_lookup.json#/$defs/get_product_response" },
           { "$ref": "../../schemas/common/types/error_response.json" }
         ]
+      },
+      "error_response": {
+        "$ref": "../../schemas/common/types/error_response.json"
       }
     }
   }