diff --git a/pkgs/code_assets/doc/schema/shared/shared_definitions.generated.schema.json b/pkgs/code_assets/doc/schema/shared/shared_definitions.generated.schema.json
index f3629226b..9bb0461d0 100644
--- a/pkgs/code_assets/doc/schema/shared/shared_definitions.generated.schema.json
+++ b/pkgs/code_assets/doc/schema/shared/shared_definitions.generated.schema.json
@@ -10,6 +10,19 @@
         },
         {
           "$ref": "../../../../hooks/doc/schema/shared/shared_definitions.schema.json#/definitions/BuildInput"
+        },
+        {
+          "properties": {
+            "assets": {
+              "type": "object",
+              "additionalProperties": {
+                "type": "array",
+                "items": {
+                  "$ref": "shared_definitions.schema.json#/definitions/Asset"
+                }
+              }
+            }
+          }
         }
       ]
     },
@@ -32,6 +45,12 @@
                 }
               }
             },
+            "assets_for_build": {
+              "type": "array",
+              "items": {
+                "$ref": "shared_definitions.schema.json#/definitions/Asset"
+              }
+            },
             "assets_for_linking": {
               "type": "object",
               "additionalProperties": {
diff --git a/pkgs/code_assets/doc/schema/shared/shared_definitions.schema.json b/pkgs/code_assets/doc/schema/shared/shared_definitions.schema.json
index 8a19e9c56..3f6089f18 100644
--- a/pkgs/code_assets/doc/schema/shared/shared_definitions.schema.json
+++ b/pkgs/code_assets/doc/schema/shared/shared_definitions.schema.json
@@ -38,10 +38,10 @@
           "type": "string",
           "anyOf": [
             {
-              "const": "native_code"
+              "const": "code_assets/code"
             },
             {
-              "const": "code_assets/code"
+              "const": "native_code"
             },
             {
               "type": "string"
@@ -54,7 +54,7 @@
           "if": {
             "properties": {
               "type": {
-                "const": "native_code"
+                "const": "code_assets/code"
               }
             }
           },
@@ -63,20 +63,14 @@
               "encoding": {
                 "$ref": "#/definitions/NativeCodeAssetEncoding"
               }
-            },
-            "allOf": [
-              {
-                "$comment": "Also include the fields parent object for backwards compatibility.",
-                "$ref": "#/definitions/NativeCodeAssetEncoding"
-              }
-            ]
+            }
           }
         },
         {
           "if": {
             "properties": {
               "type": {
-                "const": "code_assets/code"
+                "const": "native_code"
               }
             }
           },
@@ -85,7 +79,13 @@
               "encoding": {
                 "$ref": "#/definitions/NativeCodeAssetEncoding"
               }
-            }
+            },
+            "allOf": [
+              {
+                "$comment": "Also include the fields parent object for backwards compatibility.",
+                "$ref": "#/definitions/NativeCodeAssetEncoding"
+              }
+            ]
           }
         }
       ]
diff --git a/pkgs/code_assets/test/data/build_input_macos.json b/pkgs/code_assets/test/data/build_input_macos.json
index eec9ebd5b..2de3cec82 100644
--- a/pkgs/code_assets/test/data/build_input_macos.json
+++ b/pkgs/code_assets/test/data/build_input_macos.json
@@ -1,5 +1,28 @@
 {
   "$schema": "../../doc/schema/sdk/build_input.generated.schema.json",
+  "assets": {
+    "some_package": [
+      {
+        "architecture": "arm64",
+        "encoding": {
+          "architecture": "arm64",
+          "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/iv6i0d/native_add/.dart_tool/native_assets_builder/native_add/c6b312c90c95d2d98ffb6760a738fb36/out/libnative_add.a",
+          "id": "package:native_add/src/native_add_bindings_generated.dart",
+          "link_mode": {
+            "type": "static"
+          },
+          "os": "macos"
+        },
+        "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/iv6i0d/native_add/.dart_tool/native_assets_builder/native_add/c6b312c90c95d2d98ffb6760a738fb36/out/libnative_add.a",
+        "id": "package:native_add/src/native_add_bindings_generated.dart",
+        "link_mode": {
+          "type": "static"
+        },
+        "os": "macos",
+        "type": "native_code"
+      }
+    ]
+  },
   "config": {
     "build_asset_types": [
       "native_code"
diff --git a/pkgs/code_assets/test/data/build_output_macos.json b/pkgs/code_assets/test/data/build_output_macos.json
index aa64cccb0..d76fa2ef2 100644
--- a/pkgs/code_assets/test/data/build_output_macos.json
+++ b/pkgs/code_assets/test/data/build_output_macos.json
@@ -116,6 +116,27 @@
       }
     ]
   },
+  "assets_for_build": [
+    {
+      "architecture": "arm64",
+      "encoding": {
+        "architecture": "arm64",
+        "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/iv6i0d/native_add/.dart_tool/native_assets_builder/native_add/c6b312c90c95d2d98ffb6760a738fb36/out/libnative_add.a",
+        "id": "package:native_add/src/native_add_bindings_generated.dart",
+        "link_mode": {
+          "type": "static"
+        },
+        "os": "macos"
+      },
+      "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/iv6i0d/native_add/.dart_tool/native_assets_builder/native_add/c6b312c90c95d2d98ffb6760a738fb36/out/libnative_add.a",
+      "id": "package:native_add/src/native_add_bindings_generated.dart",
+      "link_mode": {
+        "type": "static"
+      },
+      "os": "macos",
+      "type": "native_code"
+    }
+  ],
   "assets_for_linking": {
     "package_with_linker": [
       {
diff --git a/pkgs/code_assets/test/schema/schema_test.dart b/pkgs/code_assets/test/schema/schema_test.dart
index fc779e91f..c879994dc 100644
--- a/pkgs/code_assets/test/schema/schema_test.dart
+++ b/pkgs/code_assets/test/schema/schema_test.dart
@@ -127,20 +127,12 @@ FieldsFunction _codeFields(AllTestData allTestData) {
         if (hook == Hook.build) ...[
           for (final (field, expect) in codeAssetFields)
             for (final encoding in _encoding)
-              for (final assetsForLinking in [
-                'assetsForLinking',
-                'assets_for_linking',
+              for (final path in [
+                ['assets_for_build'],
+                ['assetsForLinking', 'package_with_linker'],
+                ['assets_for_linking', 'package_with_linker'],
               ])
-                (
-                  [
-                    assetsForLinking,
-                    'package_with_linker',
-                    0,
-                    ...encoding,
-                    ...field,
-                  ],
-                  expect,
-                ),
+                ([...path, 0, ...encoding, ...field], expect),
         ],
         (['assets', staticIndex, 'file'], expectRequiredFieldMissing),
         (
diff --git a/pkgs/data_assets/doc/schema/shared/shared_definitions.generated.schema.json b/pkgs/data_assets/doc/schema/shared/shared_definitions.generated.schema.json
index 9e5dc0fcd..46fc0ef6b 100644
--- a/pkgs/data_assets/doc/schema/shared/shared_definitions.generated.schema.json
+++ b/pkgs/data_assets/doc/schema/shared/shared_definitions.generated.schema.json
@@ -10,6 +10,19 @@
         },
         {
           "$ref": "../../../../hooks/doc/schema/shared/shared_definitions.schema.json#/definitions/BuildInput"
+        },
+        {
+          "properties": {
+            "assets": {
+              "type": "object",
+              "additionalProperties": {
+                "type": "array",
+                "items": {
+                  "$ref": "shared_definitions.schema.json#/definitions/Asset"
+                }
+              }
+            }
+          }
         }
       ]
     },
@@ -32,6 +45,12 @@
                 }
               }
             },
+            "assets_for_build": {
+              "type": "array",
+              "items": {
+                "$ref": "shared_definitions.schema.json#/definitions/Asset"
+              }
+            },
             "assets_for_linking": {
               "type": "object",
               "additionalProperties": {
diff --git a/pkgs/data_assets/test/data/build_input.json b/pkgs/data_assets/test/data/build_input.json
index 884e7c155..2bc1f2c82 100644
--- a/pkgs/data_assets/test/data/build_input.json
+++ b/pkgs/data_assets/test/data/build_input.json
@@ -1,5 +1,31 @@
 {
   "$schema": "../../doc/schema/sdk/build_input.generated.schema.json",
+  "assets": {
+    "some_package": [
+      {
+        "encoding": {
+          "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_0.json",
+          "name": "assets/data_0.json",
+          "package": "simple_link"
+        },
+        "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_0.json",
+        "name": "assets/data_0.json",
+        "package": "simple_link",
+        "type": "data"
+      },
+      {
+        "encoding": {
+          "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_1.json",
+          "name": "assets/data_1.json",
+          "package": "simple_link"
+        },
+        "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_1.json",
+        "name": "assets/data_1.json",
+        "package": "simple_link",
+        "type": "data"
+      }
+    ]
+  },
   "config": {
     "build_asset_types": [
       "data"
diff --git a/pkgs/data_assets/test/data/build_output.json b/pkgs/data_assets/test/data/build_output.json
index e7b62ceed..d2aaca2b3 100644
--- a/pkgs/data_assets/test/data/build_output.json
+++ b/pkgs/data_assets/test/data/build_output.json
@@ -50,6 +50,30 @@
       }
     ]
   },
+  "assets_for_build": [
+    {
+      "encoding": {
+        "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_0.json",
+        "name": "assets/data_0.json",
+        "package": "simple_link"
+      },
+      "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_0.json",
+      "name": "assets/data_0.json",
+      "package": "simple_link",
+      "type": "data"
+    },
+    {
+      "encoding": {
+        "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_1.json",
+        "name": "assets/data_1.json",
+        "package": "simple_link"
+      },
+      "file": "/private/var/folders/2y/mngq9h194yzglt4kzttzfq6800klzg/T/0s5bKi/simple_link/assets/data_1.json",
+      "name": "assets/data_1.json",
+      "package": "simple_link",
+      "type": "data"
+    }
+  ],
   "assets_for_linking": {
     "package_with_linker": [
       {
diff --git a/pkgs/data_assets/test/schema/schema_test.dart b/pkgs/data_assets/test/schema/schema_test.dart
index d3b83c723..c86d79b72 100644
--- a/pkgs/data_assets/test/schema/schema_test.dart
+++ b/pkgs/data_assets/test/schema/schema_test.dart
@@ -58,14 +58,12 @@ List<(List<Object>, void Function(ValidationResults result))> _dataFields({
     if (hook == Hook.build) ...[
       for (final field in _dataAssetFields)
         for (final encoding in _encoding)
-          for (final assetsForLinking in [
-            'assetsForLinking',
-            'assets_for_linking',
+          for (final path in [
+            ['assets_for_build'],
+            ['assetsForLinking', 'package_with_linker'],
+            ['assets_for_linking', 'package_with_linker'],
           ])
-            (
-              [assetsForLinking, 'package_with_linker', 0, ...encoding, field],
-              expectRequiredFieldMissing,
-            ),
+            ([...path, 0, ...encoding, field], expectRequiredFieldMissing),
     ],
   ],
 ];
diff --git a/pkgs/hooks/doc/schema/shared/shared_definitions.schema.json b/pkgs/hooks/doc/schema/shared/shared_definitions.schema.json
index 962f983bd..b64ed7b59 100644
--- a/pkgs/hooks/doc/schema/shared/shared_definitions.schema.json
+++ b/pkgs/hooks/doc/schema/shared/shared_definitions.schema.json
@@ -6,7 +6,15 @@
       "type": "object",
       "properties": {
         "type": {
-          "type": "string"
+          "type": "string",
+          "anyOf": [
+            {
+              "const": "hooks/metadata"
+            },
+            {
+              "type": "string"
+            }
+          ]
         },
         "encoding": {
           "type": "object",
@@ -15,6 +23,27 @@
       },
       "required": [
         "type"
+      ],
+      "allOf": [
+        {
+          "if": {
+            "properties": {
+              "type": {
+                "const": "hooks/metadata"
+              }
+            }
+          },
+          "then": {
+            "properties": {
+              "encoding": {
+                "$ref": "#/definitions/MetadataAssetEncoding"
+              }
+            },
+            "required": [
+              "encoding"
+            ]
+          }
+        }
       ]
     },
     "BuildConfig": {
@@ -36,6 +65,15 @@
     },
     "BuildInput": {
       "properties": {
+        "assets": {
+          "type": "object",
+          "additionalProperties": {
+            "type": "array",
+            "items": {
+              "$ref": "#/definitions/Asset"
+            }
+          }
+        },
         "config": {
           "$ref": "#/definitions/BuildConfig"
         },
@@ -65,6 +103,12 @@
             }
           }
         },
+        "assets_for_build": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/Asset"
+          }
+        },
         "assets_for_linking": {
           "type": "object",
           "additionalProperties": {
@@ -196,6 +240,18 @@
         }
       ]
     },
+    "MetadataAssetEncoding": {
+      "type": "object",
+      "properties": {
+        "key": {
+          "type": "string"
+        },
+        "value": {}
+      },
+      "required": [
+        "key"
+      ]
+    },
     "absolutePath": {
       "type": "string",
       "pattern": "^(\\/|[A-Za-z]:)"
diff --git a/pkgs/hooks/test/data/build_input.json b/pkgs/hooks/test/data/build_input.json
index 93f78e86a..8b7d189d0 100644
--- a/pkgs/hooks/test/data/build_input.json
+++ b/pkgs/hooks/test/data/build_input.json
@@ -1,5 +1,20 @@
 {
   "$schema": "../../doc/schema/sdk/build_input.generated.schema.json",
+  "assets": {
+    "some_package": [
+      {
+        "encoding": {
+          "key": "foo",
+          "value": "bar"
+        },
+        "type": "hooks/metadata"
+      },
+      {
+        "some_key": "some_value",
+        "type": "some_asset_type"
+      }
+    ]
+  },
   "config": {
     "build_asset_types": [
       "my_asset_type"
diff --git a/pkgs/hooks/test/data/build_output.json b/pkgs/hooks/test/data/build_output.json
index cffa92ce5..368ca06e5 100644
--- a/pkgs/hooks/test/data/build_output.json
+++ b/pkgs/hooks/test/data/build_output.json
@@ -20,35 +20,51 @@
     "package_with_linker": [
       {
         "encoding": {
-          "some_key": "some_value"
+          "a_key": "some_value"
         },
         "some_key": "some_value",
         "type": "some_asset_type"
       },
       {
         "encoding": {
-          "some_other_key": "some_value"
+          "key": "foo",
+          "value": "bar"
         },
-        "some_other_key": "some_value",
-        "type": "some_other_asset_type"
+        "type": "hooks/metadata"
       }
     ]
   },
+  "assets_for_build": [
+    {
+      "encoding": {
+        "a_key": "some_value"
+      },
+      "some_key": "some_value",
+      "type": "some_asset_type"
+    },
+    {
+      "encoding": {
+        "key": "foo",
+        "value": "bar"
+      },
+      "type": "hooks/metadata"
+    }
+  ],
   "assets_for_linking": {
     "package_with_linker": [
       {
         "encoding": {
-          "some_key": "some_value"
+          "a_key": "some_value"
         },
         "some_key": "some_value",
         "type": "some_asset_type"
       },
       {
         "encoding": {
-          "some_other_key": "some_value"
+          "key": "foo",
+          "value": "bar"
         },
-        "some_other_key": "some_value",
-        "type": "some_other_asset_type"
+        "type": "hooks/metadata"
       }
     ]
   },
diff --git a/pkgs/hooks/test/data/link_input.json b/pkgs/hooks/test/data/link_input.json
index 351184a89..2e13e31db 100644
--- a/pkgs/hooks/test/data/link_input.json
+++ b/pkgs/hooks/test/data/link_input.json
@@ -2,12 +2,15 @@
   "$schema": "../../doc/schema/sdk/link_input.generated.schema.json",
   "assets": [
     {
-      "some_key": "some_value",
+      "a_key": "some_value",
       "type": "some_asset_type"
     },
     {
-      "some_other_key": "some_value",
-      "type": "some_other_asset_type"
+      "encoding": {
+        "key": "foo",
+        "value": "bar"
+      },
+      "type": "hooks/metadata"
     }
   ],
   "config": {
diff --git a/pkgs/hooks/test/schema/helpers.dart b/pkgs/hooks/test/schema/helpers.dart
index 862c5e83d..ad2c876fc 100644
--- a/pkgs/hooks/test/schema/helpers.dart
+++ b/pkgs/hooks/test/schema/helpers.dart
@@ -159,13 +159,14 @@ void testAllTestData(AllSchemas allSchemas, AllTestData allTestData) {
 /// [missingExpectations].
 void testField({
   required Uri schemaUri,
+  required Uri dataUri,
   required JsonSchema schema,
   required String data,
   required List<Object> field,
   required void Function(ValidationResults result) missingExpectations,
 }) {
   final fieldPath = field.join('.');
-  test('$schemaUri $fieldPath missing', () {
+  test('$schemaUri $dataUri $fieldPath missing', () {
     final dataDecoded = jsonDecode(data);
     final dataToModify = _traverseJson(
       dataDecoded,
@@ -254,6 +255,7 @@ void testFields({
             field: field,
             schemaUri: schemaUri,
             schema: schema,
+            dataUri: dataUri,
             data: data,
             missingExpectations: missingExpectations,
           );
@@ -342,27 +344,34 @@ FieldsReturn _hookFields({
       (['timestamp'], expectRequiredFieldMissing),
       (['dependencies'], expectOptionalFieldMissing),
       (['dependencies', 0], expectOptionalFieldMissing),
-      (['assets'], expectOptionalFieldMissing),
-      (['assets', 0], expectOptionalFieldMissing),
-      (['assets', 0, 'encoding'], expectOptionalFieldMissing),
-      (['assets', 0, 'type'], expectRequiredFieldMissing),
-      if (hook == Hook.build)
-        for (final assetsForLinking in [
-          'assetsForLinking',
-          'assets_for_linking',
+
+      if (hook == Hook.build) ...[
+        (['metadata'], expectOptionalFieldMissing),
+        for (final path in [
+          ['assets_for_build'],
+          ['assetsForLinking', 'package_with_linker'],
+          ['assets_for_linking', 'package_with_linker'],
         ]) ...[
-          (['metadata'], expectOptionalFieldMissing),
-          ([assetsForLinking], expectOptionalFieldMissing),
-          (
-            [assetsForLinking, 'package_with_linker', 0],
-            expectOptionalFieldMissing,
-          ),
-          ([assetsForLinking], expectOptionalFieldMissing),
-          (
-            [assetsForLinking, 'package_with_linker', 0, 'type'],
-            expectRequiredFieldMissing,
-          ),
+          ([...path], expectOptionalFieldMissing),
+          ([...path, 0], expectOptionalFieldMissing),
+          ([...path, 0, 'type'], expectRequiredFieldMissing),
+          ([...path, 0, 'encoding'], expectOptionalFieldMissing),
         ],
+      ],
+    ],
+    for (final path in [
+      if (inputOrOutput == InputOrOutput.output || hook == Hook.link)
+        ['assets'],
+      if (inputOrOutput == InputOrOutput.output && hook == Hook.build) ...[
+        ['assets_for_build'],
+        ['assetsForLinking', 'package_with_linker'],
+        ['assets_for_linking', 'package_with_linker'],
+      ],
+    ]) ...[
+      ([...path], expectOptionalFieldMissing),
+      ([...path, 0], expectOptionalFieldMissing),
+      ([...path, 0, 'type'], expectRequiredFieldMissing),
+      ([...path, 0, 'encoding'], expectOptionalFieldMissing),
     ],
   ];
 }
diff --git a/pkgs/hooks/test/schema/schema_test.dart b/pkgs/hooks/test/schema/schema_test.dart
index c163281d7..51a0cf2a2 100644
--- a/pkgs/hooks/test/schema/schema_test.dart
+++ b/pkgs/hooks/test/schema/schema_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:json_schema/json_schema.dart';
+
 import 'helpers.dart';
 
 void main() {
@@ -19,6 +21,35 @@ void main() {
     allTestData: allTestData,
     packageUri: packageUri,
   );
+
+  testFields(
+    allSchemas: allSchemas,
+    allTestData: allTestData,
+    packageUri: packageUri,
+    fields: _metadataAssetFields,
+  );
 }
 
 Uri packageUri = findPackageRoot('hooks');
+
+List<(List<Object>, void Function(ValidationResults result))>
+_metadataAssetFields({
+  required InputOrOutput inputOrOutput,
+  required Hook hook,
+  required Party party,
+}) => <(List<Object>, void Function(ValidationResults result))>[
+  for (final path in [
+    if (inputOrOutput == InputOrOutput.input && hook == Hook.link) ['assets'],
+    if (inputOrOutput == InputOrOutput.output && hook == Hook.build) ...[
+      ['assets_for_build'],
+      ['assetsForLinking', 'package_with_linker'],
+      ['assets_for_linking', 'package_with_linker'],
+    ],
+  ]) ...[
+    ([...path, 1], expectOptionalFieldMissing),
+    ([...path, 1, 'type'], expectRequiredFieldMissing),
+    ([...path, 1, 'encoding'], expectRequiredFieldMissing),
+    ([...path, 1, 'encoding', 'key'], expectRequiredFieldMissing),
+    // Skip `encoding.value`, it's optional and may have any type.
+  ],
+];
diff --git a/pkgs/hooks/tool/generate_schemas.dart b/pkgs/hooks/tool/generate_schemas.dart
index e13c9d77a..e00cea7ec 100644
--- a/pkgs/hooks/tool/generate_schemas.dart
+++ b/pkgs/hooks/tool/generate_schemas.dart
@@ -52,6 +52,23 @@ void generateSharedDefinitions() {
           },
         },
       },
+      'assets_for_build': {
+        'type': 'array',
+        'items': {r'$ref': 'shared_definitions.schema.json#/definitions/Asset'},
+      },
+    },
+  };
+  const buildInputAssetOverride = {
+    'properties': {
+      'assets': {
+        'type': 'object',
+        'additionalProperties': {
+          'type': 'array',
+          'items': {
+            r'$ref': 'shared_definitions.schema.json#/definitions/Asset',
+          },
+        },
+      },
     },
   };
   const linkInputAssetOverride = {
@@ -128,6 +145,10 @@ void generateSharedDefinitions() {
                       hook == Hook.hook &&
                       inputOrOutput == InputOrOutput.output)
                     hookOutputAssetOverride,
+                  if (party == Party.shared &&
+                      hook == Hook.build &&
+                      inputOrOutput == InputOrOutput.input)
+                    buildInputAssetOverride,
                   if (party == Party.shared &&
                       hook == Hook.link &&
                       inputOrOutput == InputOrOutput.input)
diff --git a/pkgs/json_syntax_generator/lib/src/parser/schema_analyzer.dart b/pkgs/json_syntax_generator/lib/src/parser/schema_analyzer.dart
index 9df0eab7d..fe1f14e78 100644
--- a/pkgs/json_syntax_generator/lib/src/parser/schema_analyzer.dart
+++ b/pkgs/json_syntax_generator/lib/src/parser/schema_analyzer.dart
@@ -180,13 +180,18 @@ class SchemaAnalyzer {
       properties: properties,
       taggedUnionValue: taggedUnionValue,
       taggedUnionProperty:
-          schemas.generateSubClasses ? properties.single.name : null,
+          schemas.generateSubClasses ? schemas.generateSubClassesKey! : null,
       visibleTaggedUnion: visbleUnionTagValues.contains(typeName),
       extraValidation: extraValidation,
     );
     _classes[typeName] = classInfo;
     if (schemas.generateSubClasses) {
-      _analyzeSubClasses(schemas, name: name, superclass: classInfo);
+      _analyzeSubClasses(
+        schemas,
+        schemas.generateSubClassesKey!,
+        name: name,
+        superclass: classInfo,
+      );
       return;
     }
   }
@@ -251,13 +256,13 @@ class SchemaAnalyzer {
   }
 
   void _analyzeSubClasses(
-    JsonSchemas schemas, {
+    JsonSchemas schemas,
+    String propertyKey, {
     String? name,
     NormalClassInfo? superclass,
   }) {
     final typeName = schemas.className;
 
-    final propertyKey = schemas.propertyKeys.single;
     final typeProperty = schemas.property(propertyKey);
     final subTypes = typeProperty.enumOrTaggedUnionValues;
     for (final subType in subTypes) {
@@ -299,6 +304,8 @@ class SchemaAnalyzer {
     final type = schemas.type;
     final DartType dartType;
     switch (type) {
+      case null:
+        dartType = ObjectDartType(isNullable: !required);
       case SchemaType.boolean:
         dartType = BoolDartType(isNullable: !required);
       case SchemaType.integer:
@@ -650,10 +657,21 @@ extension on JsonSchemas {
       (additionalPropertiesSchemas.isNotEmpty ||
           additionalPropertiesBool == true);
 
-  bool get generateSubClasses =>
-      type == SchemaType.object &&
-      propertyKeys.length == 1 &&
-      property(propertyKeys.single).anyOfs.isNotEmpty;
+  bool get generateSubClasses => generateSubClassesKey != null;
+
+  String? get generateSubClassesKey {
+    if (type != SchemaType.object) return null;
+    // A tagged union either has only a key, or a key and an encoding.
+    // Classes with more than 2 properties have their a property that has
+    // predefined values generated as an enum class.
+    if (propertyKeys.length > 2) return null;
+    for (final p in propertyKeys) {
+      if (property(p).anyOfs.isNotEmpty) {
+        return p;
+      }
+    }
+    return null;
+  }
 
   bool get generateClass => type == SchemaType.object && !generateMapOf;
 
diff --git a/pkgs/native_assets_cli/lib/src/config.dart b/pkgs/native_assets_cli/lib/src/config.dart
index 7ff89a73a..d1e6e256d 100644
--- a/pkgs/native_assets_cli/lib/src/config.dart
+++ b/pkgs/native_assets_cli/lib/src/config.dart
@@ -183,6 +183,7 @@ final class BuildInputBuilder extends HookInputBuilder {
       dependencyMetadata: {
         for (final key in metadata.keys) key: metadata[key]!.toJson(),
       },
+      assets: null, // TODO: Implement this.
     );
   }
 
diff --git a/pkgs/native_assets_cli/lib/src/hooks/syntax.g.dart b/pkgs/native_assets_cli/lib/src/hooks/syntax.g.dart
index 92a209611..cb44527f2 100644
--- a/pkgs/native_assets_cli/lib/src/hooks/syntax.g.dart
+++ b/pkgs/native_assets_cli/lib/src/hooks/syntax.g.dart
@@ -11,7 +11,18 @@
 import 'dart:io';
 
 class Asset extends JsonObject {
-  Asset.fromJson(super.json, {super.path = const []}) : super.fromJson();
+  factory Asset.fromJson(
+    Map<String, Object?> json, {
+    List<Object> path = const [],
+  }) {
+    final result = Asset._fromJson(json, path: path);
+    if (result.isHooksMetadataAsset) {
+      return result.asHooksMetadataAsset;
+    }
+    return result;
+  }
+
+  Asset._fromJson(super.json, {super.path = const []}) : super.fromJson();
 
   Asset({required JsonObject? encoding, required String type}) : super() {
     _encoding = encoding;
@@ -50,8 +61,25 @@ class Asset extends JsonObject {
     ...super.validate(),
     ..._validateEncoding(),
     ..._validateType(),
+    ..._validateExtraRules(),
   ];
 
+  List<String> _validateExtraRules() {
+    final result = <String>[];
+    if (_reader.tryTraverse(['type']) == 'hooks/metadata') {
+      final objectErrors = _reader.validate<Map<String, Object?>?>('encoding');
+      result.addAll(objectErrors);
+      if (objectErrors.isEmpty) {
+        final jsonValue = _reader.get<Map<String, Object?>?>('encoding');
+        if (jsonValue != null) {
+          final reader = JsonReader(jsonValue, [...path, 'encoding']);
+          result.addAll(reader.validate<Object>('key'));
+        }
+      }
+    }
+    return result;
+  }
+
   @override
   String toString() => 'Asset($json)';
 }
@@ -98,6 +126,7 @@ class BuildInput extends HookInput {
   BuildInput.fromJson(super.json, {super.path}) : super.fromJson();
 
   BuildInput({
+    required Map<String, List<Asset>>? assets,
     required BuildConfig config,
     required Map<String, Map<String, Object?>>? dependencyMetadata,
     required super.outDir,
@@ -107,17 +136,69 @@ class BuildInput extends HookInput {
     required super.packageRoot,
     required super.version,
   }) : super(config: config) {
+    _assets = assets;
     _dependencyMetadata = dependencyMetadata;
     json.sortOnKey();
   }
 
   /// Setup all fields for [BuildInput] that are not in
   /// [HookInput].
-  void setup({required Map<String, Map<String, Object?>>? dependencyMetadata}) {
+  void setup({
+    required Map<String, List<Asset>>? assets,
+    required Map<String, Map<String, Object?>>? dependencyMetadata,
+  }) {
+    _assets = assets;
     _dependencyMetadata = dependencyMetadata;
     json.sortOnKey();
   }
 
+  Map<String, List<Asset>>? get assets {
+    final jsonValue = _reader.optionalMap('assets');
+    if (jsonValue == null) {
+      return null;
+    }
+    final result = <String, List<Asset>>{};
+    for (final MapEntry(:key, :value) in jsonValue.entries) {
+      result[key] = [
+        for (final (index, item) in (value as List<Object?>).indexed)
+          Asset.fromJson(
+            item as Map<String, Object?>,
+            path: [...path, key, index],
+          ),
+      ];
+    }
+    return result;
+  }
+
+  set _assets(Map<String, List<Asset>>? value) {
+    if (value == null) {
+      json.remove('assets');
+    } else {
+      json['assets'] = {
+        for (final MapEntry(:key, :value) in value.entries)
+          key: [for (final item in value) item.json],
+      };
+    }
+  }
+
+  List<String> _validateAssets() {
+    final mapErrors = _reader.validateOptionalMap('assets');
+    if (mapErrors.isNotEmpty) {
+      return mapErrors;
+    }
+    final jsonValue = _reader.optionalMap('assets');
+    if (jsonValue == null) {
+      return [];
+    }
+    final result = <String>[];
+    for (final list in assets!.values) {
+      for (final element in list) {
+        result.addAll(element.validate());
+      }
+    }
+    return result;
+  }
+
   @override
   BuildConfig get config {
     final jsonValue = _reader.map$('config');
@@ -137,6 +218,7 @@ class BuildInput extends HookInput {
   @override
   List<String> validate() => [
     ...super.validate(),
+    ..._validateAssets(),
     ..._validateConfig(),
     ..._validateDependencyMetadata(),
   ];
@@ -150,6 +232,7 @@ class BuildOutput extends HookOutput {
 
   BuildOutput({
     required super.assets,
+    required List<Asset>? assetsForBuild,
     required Map<String, List<Asset>>? assetsForLinking,
     required Map<String, List<Asset>>? assetsForLinkingOld,
     required super.dependencies,
@@ -158,6 +241,7 @@ class BuildOutput extends HookOutput {
     required super.version,
   }) : super() {
     this.assetsForLinkingOld = assetsForLinkingOld;
+    this.assetsForBuild = assetsForBuild;
     this.assetsForLinking = assetsForLinking;
     this.metadata = metadata;
     json.sortOnKey();
@@ -167,10 +251,12 @@ class BuildOutput extends HookOutput {
   /// [HookOutput].
   void setup({
     required Map<String, List<Asset>>? assetsForLinkingOld,
+    required List<Asset>? assetsForBuild,
     required Map<String, List<Asset>>? assetsForLinking,
     required JsonObject? metadata,
   }) {
     this.assetsForLinkingOld = assetsForLinkingOld;
+    this.assetsForBuild = assetsForBuild;
     this.assetsForLinking = assetsForLinking;
     this.metadata = metadata;
     json.sortOnKey();
@@ -224,6 +310,41 @@ class BuildOutput extends HookOutput {
     return result;
   }
 
+  List<Asset>? get assetsForBuild {
+    final jsonValue = _reader.optionalList('assets_for_build');
+    if (jsonValue == null) return null;
+    return [
+      for (final (index, element) in jsonValue.indexed)
+        Asset.fromJson(
+          element as Map<String, Object?>,
+          path: [...path, 'assets_for_build', index],
+        ),
+    ];
+  }
+
+  set assetsForBuild(List<Asset>? value) {
+    if (value == null) {
+      json.remove('assets_for_build');
+    } else {
+      json['assets_for_build'] = [for (final item in value) item.json];
+    }
+    json.sortOnKey();
+  }
+
+  List<String> _validateAssetsForBuild() {
+    final listErrors = _reader.validateOptionalList<Map<String, Object?>>(
+      'assets_for_build',
+    );
+    if (listErrors.isNotEmpty) {
+      return listErrors;
+    }
+    final elements = assetsForBuild;
+    if (elements == null) {
+      return [];
+    }
+    return [for (final element in elements) ...element.validate()];
+  }
+
   Map<String, List<Asset>>? get assetsForLinking {
     final jsonValue = _reader.optionalMap('assets_for_linking');
     if (jsonValue == null) {
@@ -295,6 +416,7 @@ class BuildOutput extends HookOutput {
   List<String> validate() => [
     ...super.validate(),
     ..._validateAssetsForLinkingOld(),
+    ..._validateAssetsForBuild(),
     ..._validateAssetsForLinking(),
     ..._validateMetadata(),
   ];
@@ -559,6 +681,41 @@ class HookOutput extends JsonObject {
   String toString() => 'HookOutput($json)';
 }
 
+class HooksMetadataAsset extends Asset {
+  static const typeValue = 'hooks/metadata';
+
+  HooksMetadataAsset.fromJson(super.json, {super.path}) : super._fromJson();
+
+  HooksMetadataAsset({required MetadataAssetEncoding encoding})
+    : super(type: 'hooks/metadata', encoding: encoding);
+
+  /// Setup all fields for [HooksMetadataAsset] that are not in
+  /// [Asset].
+  void setup() {}
+
+  @override
+  MetadataAssetEncoding get encoding {
+    final jsonValue = _reader.map$('encoding');
+    return MetadataAssetEncoding.fromJson(
+      jsonValue,
+      path: [...path, 'encoding'],
+    );
+  }
+
+  @override
+  List<String> validate() => [...super.validate(), ..._validateEncoding()];
+
+  @override
+  String toString() => 'HooksMetadataAsset($json)';
+}
+
+extension HooksMetadataAssetExtension on Asset {
+  bool get isHooksMetadataAsset => type == 'hooks/metadata';
+
+  HooksMetadataAsset get asHooksMetadataAsset =>
+      HooksMetadataAsset.fromJson(json, path: path);
+}
+
 class LinkInput extends HookInput {
   LinkInput.fromJson(super.json, {super.path}) : super.fromJson();
 
@@ -660,6 +817,44 @@ class LinkOutput extends HookOutput {
   String toString() => 'LinkOutput($json)';
 }
 
+class MetadataAssetEncoding extends JsonObject {
+  MetadataAssetEncoding.fromJson(super.json, {super.path = const []})
+    : super.fromJson();
+
+  MetadataAssetEncoding({required String key, required Object? value})
+    : super() {
+    _key = key;
+    _value = value;
+    json.sortOnKey();
+  }
+
+  String get key => _reader.get<String>('key');
+
+  set _key(String value) {
+    json.setOrRemove('key', value);
+  }
+
+  List<String> _validateKey() => _reader.validate<String>('key');
+
+  Object? get value => _reader.get<Object?>('value');
+
+  set _value(Object? value) {
+    json.setOrRemove('value', value);
+  }
+
+  List<String> _validateValue() => _reader.validate<Object?>('value');
+
+  @override
+  List<String> validate() => [
+    ...super.validate(),
+    ..._validateKey(),
+    ..._validateValue(),
+  ];
+
+  @override
+  String toString() => 'MetadataAssetEncoding($json)';
+}
+
 class JsonObject {
   final Map<String, Object?> json;