diff --git a/buffet/commands/command_definition.cc b/buffet/commands/command_definition.cc
index f24b22d..7494de8 100644
--- a/buffet/commands/command_definition.cc
+++ b/buffet/commands/command_definition.cc
@@ -8,8 +8,9 @@
 
 CommandDefinition::CommandDefinition(
     const std::string& category,
-    const std::shared_ptr<const ObjectSchema>& parameters)
-        : category_(category), parameters_(parameters) {
+    const std::shared_ptr<const ObjectSchema>& parameters,
+    const std::shared_ptr<const ObjectSchema>& results)
+        : category_(category), parameters_(parameters), results_(results) {
 }
 
 }  // namespace buffet
diff --git a/buffet/commands/command_definition.h b/buffet/commands/command_definition.h
index f02cf48..a7b793a 100644
--- a/buffet/commands/command_definition.h
+++ b/buffet/commands/command_definition.h
@@ -22,7 +22,8 @@
 class CommandDefinition {
  public:
   CommandDefinition(const std::string& category,
-                    const std::shared_ptr<const ObjectSchema>& parameters);
+                    const std::shared_ptr<const ObjectSchema>& parameters,
+                    const std::shared_ptr<const ObjectSchema>& results);
 
   // Gets the category this command belongs to.
   const std::string& GetCategory() const { return category_; }
@@ -30,10 +31,15 @@
   const std::shared_ptr<const ObjectSchema>& GetParameters() const {
     return parameters_;
   }
+  // Gets the object schema for command results.
+  const std::shared_ptr<const ObjectSchema>& GetResults() const {
+    return results_;
+  }
 
  private:
   std::string category_;  // Cmd category. Could be "powerd" for "base.reboot".
-  std::shared_ptr<const ObjectSchema> parameters_;  // Command parameter def.
+  std::shared_ptr<const ObjectSchema> parameters_;  // Command parameters def.
+  std::shared_ptr<const ObjectSchema> results_;  // Command results def.
   DISALLOW_COPY_AND_ASSIGN(CommandDefinition);
 };
 
diff --git a/buffet/commands/command_definition_unittest.cc b/buffet/commands/command_definition_unittest.cc
index f0adab1..0b06086 100644
--- a/buffet/commands/command_definition_unittest.cc
+++ b/buffet/commands/command_definition_unittest.cc
@@ -8,7 +8,9 @@
 
 TEST(CommandDefinition, Test) {
   auto params = std::make_shared<buffet::ObjectSchema>();
-  buffet::CommandDefinition def("powerd", params);
+  auto results = std::make_shared<buffet::ObjectSchema>();
+  buffet::CommandDefinition def("powerd", params, results);
   EXPECT_EQ("powerd", def.GetCategory());
   EXPECT_EQ(params, def.GetParameters());
+  EXPECT_EQ(results, def.GetResults());
 }
diff --git a/buffet/commands/command_dictionary.cc b/buffet/commands/command_dictionary.cc
index 98ffefc..930e044 100644
--- a/buffet/commands/command_dictionary.cc
+++ b/buffet/commands/command_dictionary.cc
@@ -54,8 +54,8 @@
             package_name.c_str());
         return false;
       }
-      const base::DictionaryValue* command_value = nullptr;
-      if (!command_iter.value().GetAsDictionary(&command_value)) {
+      const base::DictionaryValue* command_def_json = nullptr;
+      if (!command_iter.value().GetAsDictionary(&command_def_json)) {
         chromeos::Error::AddToPrintf(error, FROM_HERE,
                                      errors::commands::kDomain,
                                      errors::commands::kTypeMismatch,
@@ -66,32 +66,22 @@
       // Construct the compound command name as "pkg_name.cmd_name".
       std::string full_command_name = chromeos::string_utils::Join(
           '.', package_name, command_name);
-      // Get the "parameters" definition of the command and read it into
-      // an object schema.
-      const base::DictionaryValue* command_schema_def = nullptr;
-      if (!command_value->GetDictionaryWithoutPathExpansion(
-          commands::attributes::kCommand_Parameters, &command_schema_def)) {
-        chromeos::Error::AddToPrintf(
-            error, FROM_HERE, errors::commands::kDomain,
-            errors::commands::kPropertyMissing,
-            "Command definition '%s' is missing property '%s'",
-            full_command_name.c_str(),
-            commands::attributes::kCommand_Parameters);
-        return false;
-      }
 
-      const ObjectSchema* base_def = nullptr;
+      const ObjectSchema* base_parameters_def = nullptr;
+      const ObjectSchema* base_results_def = nullptr;
       if (base_commands) {
         const CommandDefinition* cmd =
             base_commands->FindCommand(full_command_name);
-        if (cmd)
-          base_def = cmd->GetParameters().get();
+        if (cmd) {
+          base_parameters_def = cmd->GetParameters().get();
+          base_results_def = cmd->GetResults().get();
+        }
 
         // If the base command dictionary was provided but the command was not
         // found in it, this must be a custom (vendor) command. GCD spec states
         // that all custom command names must begin with "_". Let's enforce
         // this rule here.
-        if (!base_def) {
+        if (!cmd) {
           if (command_name.front() != '_') {
             chromeos::Error::AddToPrintf(
                 error, FROM_HERE, errors::commands::kDomain,
@@ -104,17 +94,27 @@
         }
       }
 
-      auto command_schema = std::make_shared<ObjectSchema>();
-      if (!command_schema->FromJson(command_schema_def, base_def, error)) {
-        chromeos::Error::AddToPrintf(error, FROM_HERE,
-                                     errors::commands::kDomain,
-                                     errors::commands::kInvalidObjectSchema,
-                                     "Invalid definition for command '%s'",
-                                     full_command_name.c_str());
+      auto parameters_schema = BuildObjectSchema(
+          command_def_json,
+          commands::attributes::kCommand_Parameters,
+          base_parameters_def,
+          full_command_name,
+          error);
+      if (!parameters_schema)
         return false;
-      }
+
+      auto results_schema = BuildObjectSchema(
+          command_def_json,
+          commands::attributes::kCommand_Results,
+          base_results_def,
+          full_command_name,
+          error);
+      if (!results_schema)
+        return false;
+
       auto command_def = std::make_shared<CommandDefinition>(category,
-                                                             command_schema);
+                                                             parameters_schema,
+                                                             results_schema);
       new_defs.insert(std::make_pair(full_command_name, command_def));
 
       command_iter.Advance();
@@ -150,6 +150,38 @@
   return true;
 }
 
+std::shared_ptr<ObjectSchema> CommandDictionary::BuildObjectSchema(
+    const base::DictionaryValue* command_def_json,
+    const char* property_name,
+    const ObjectSchema* base_def,
+    const std::string& command_name,
+    chromeos::ErrorPtr* error) {
+  auto object_schema = std::make_shared<ObjectSchema>();
+
+  const base::DictionaryValue* schema_def = nullptr;
+  if (!command_def_json->GetDictionaryWithoutPathExpansion(property_name,
+                                                           &schema_def)) {
+    chromeos::Error::AddToPrintf(
+        error, FROM_HERE, errors::commands::kDomain,
+        errors::commands::kPropertyMissing,
+        "Command definition '%s' is missing property '%s'",
+        command_name.c_str(),
+        property_name);
+    return {};
+  }
+
+  if (!object_schema->FromJson(schema_def, base_def, error)) {
+    chromeos::Error::AddToPrintf(error, FROM_HERE,
+                                 errors::commands::kDomain,
+                                 errors::commands::kInvalidObjectSchema,
+                                 "Invalid definition for command '%s'",
+                                 command_name.c_str());
+    return {};
+  }
+
+  return object_schema;
+}
+
 std::unique_ptr<base::DictionaryValue> CommandDictionary::GetCommandsAsJson(
     bool full_schema, chromeos::ErrorPtr* error) const {
   std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue);
diff --git a/buffet/commands/command_dictionary.h b/buffet/commands/command_dictionary.h
index bd60986..c316fd5 100644
--- a/buffet/commands/command_dictionary.h
+++ b/buffet/commands/command_dictionary.h
@@ -21,6 +21,7 @@
 namespace buffet {
 
 class CommandDefinition;
+class ObjectSchema;
 
 // CommandDictionary is a wrapper around a map of command name and the
 // corresponding command definition schema. The command name (the key in
@@ -71,6 +72,13 @@
   const CommandDefinition* FindCommand(const std::string& command_name) const;
 
  private:
+  std::shared_ptr<ObjectSchema> BuildObjectSchema(
+      const base::DictionaryValue* command_def_json,
+      const char* property_name,
+      const ObjectSchema* base_def,
+      const std::string& command_name,
+      chromeos::ErrorPtr* error);
+
   using CommandMap = std::map<std::string,
                               std::shared_ptr<const CommandDefinition>>;
 
diff --git a/buffet/commands/command_dictionary_unittest.cc b/buffet/commands/command_dictionary_unittest.cc
index 20c1287..10e7ec9 100644
--- a/buffet/commands/command_dictionary_unittest.cc
+++ b/buffet/commands/command_dictionary_unittest.cc
@@ -24,7 +24,8 @@
         'parameters': {
           'height': 'integer',
           '_jumpType': ['_withAirFlip', '_withSpin', '_withKick']
-        }
+        },
+        'results': {}
       }
     }
   })");
@@ -35,10 +36,12 @@
   json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       },
       'shutdown': {
-        'parameters': {}
+        'parameters': {},
+        'results': {}
       }
     }
   })");
@@ -57,13 +60,21 @@
   chromeos::ErrorPtr error;
 
   // Command definition missing 'parameters' property.
-  auto json = CreateDictionaryValue("{'robot':{'jump':{}}}");
+  auto json = CreateDictionaryValue("{'robot':{'jump':{'results':{}}}}");
   EXPECT_FALSE(dict.LoadCommands(*json, "robotd", nullptr, &error));
   EXPECT_EQ("parameter_missing", error->GetCode());
   EXPECT_EQ("Command definition 'robot.jump' is missing property 'parameters'",
             error->GetMessage());
   error.reset();
 
+  // Command definition missing 'results' property.
+  json = CreateDictionaryValue("{'robot':{'jump':{'parameters':{}}}}");
+  EXPECT_FALSE(dict.LoadCommands(*json, "robotd", nullptr, &error));
+  EXPECT_EQ("parameter_missing", error->GetCode());
+  EXPECT_EQ("Command definition 'robot.jump' is missing property 'results'",
+            error->GetMessage());
+  error.reset();
+
   // Command definition is not an object.
   json = CreateDictionaryValue("{'robot':{'jump':0}}");
   EXPECT_FALSE(dict.LoadCommands(*json, "robotd", nullptr, &error));
@@ -79,7 +90,8 @@
   error.reset();
 
   // Invalid command definition is not an object.
-  json = CreateDictionaryValue("{'robot':{'jump':{'parameters':{'flip':0}}}}");
+  json = CreateDictionaryValue(
+      "{'robot':{'jump':{'parameters':{'flip':0},'results':{}}}}");
   EXPECT_FALSE(dict.LoadCommands(*json, "robotd", nullptr, &error));
   EXPECT_EQ("invalid_object_schema", error->GetCode());
   EXPECT_EQ("Invalid definition for command 'robot.jump'", error->GetMessage());
@@ -87,7 +99,7 @@
   error.reset();
 
   // Empty command name.
-  json = CreateDictionaryValue("{'robot':{'':{'parameters':{'flip':0}}}}");
+  json = CreateDictionaryValue("{'robot':{'':{'parameters':{},'results':{}}}}");
   EXPECT_FALSE(dict.LoadCommands(*json, "robotd", nullptr, &error));
   EXPECT_EQ("invalid_command_name", error->GetCode());
   EXPECT_EQ("Unnamed command encountered in package 'robot'",
@@ -99,7 +111,8 @@
   // Redefine commands in different category.
   buffet::CommandDictionary dict;
   chromeos::ErrorPtr error;
-  auto json = CreateDictionaryValue("{'robot':{'jump':{'parameters':{}}}}");
+  auto json = CreateDictionaryValue(
+      "{'robot':{'jump':{'parameters':{},'results':{}}}}");
   dict.LoadCommands(*json, "category1", nullptr, &error);
   EXPECT_FALSE(dict.LoadCommands(*json, "category2", nullptr, &error));
   EXPECT_EQ("duplicate_command_definition", error->GetCode());
@@ -116,13 +129,15 @@
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       }
     }
   })");
   base_dict.LoadCommands(*json, "", nullptr, &error);
   EXPECT_TRUE(dict.LoadCommands(*json, "robotd", &base_dict, &error));
-  auto json2 = CreateDictionaryValue("{'base':{'jump':{'parameters':{}}}}");
+  auto json2 = CreateDictionaryValue(
+      "{'base':{'jump':{'parameters':{},'results':{}}}}");
   EXPECT_FALSE(dict.LoadCommands(*json2, "robotd", &base_dict, &error));
   EXPECT_EQ("invalid_command_name", error->GetCode());
   EXPECT_EQ("The name of custom command 'jump' in package 'base' must start "
@@ -130,7 +145,8 @@
   error.reset();
 
   // If the command starts with "_", then it's Ok.
-  json2 = CreateDictionaryValue("{'base':{'_jump':{'parameters':{}}}}");
+  json2 = CreateDictionaryValue(
+      "{'base':{'_jump':{'parameters':{},'results':{}}}}");
   EXPECT_TRUE(dict.LoadCommands(*json2, "robotd", &base_dict, nullptr));
 }
 
@@ -142,15 +158,18 @@
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {'version': 'integer'}
       }
     }
   })");
   base_dict.LoadCommands(*json, "", nullptr, &error);
+
   auto json2 = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'string'}
+        'parameters': {'delay': 'string'},
+        'results': {'version': 'integer'}
       }
     }
   })");
@@ -165,16 +184,39 @@
   EXPECT_EQ("Redefining a property of type integer as string",
             error->GetFirstError()->GetMessage());
   error.reset();
+
+  auto json3 = CreateDictionaryValue(R"({
+    'base': {
+      'reboot': {
+        'parameters': {'delay': 'integer'},
+        'results': {'version': 'string'}
+      }
+    }
+  })");
+  EXPECT_FALSE(dict.LoadCommands(*json3, "robotd", &base_dict, &error));
+  EXPECT_EQ("invalid_object_schema", error->GetCode());
+  EXPECT_EQ("Invalid definition for command 'base.reboot'",
+            error->GetMessage());
+  // TODO(antonm): remove parameter from error below and use some generic.
+  EXPECT_EQ("invalid_parameter_definition", error->GetInnerError()->GetCode());
+  EXPECT_EQ("Error in definition of property 'version'",
+            error->GetInnerError()->GetMessage());
+  EXPECT_EQ("param_type_changed", error->GetFirstError()->GetCode());
+  EXPECT_EQ("Redefining a property of type integer as string",
+            error->GetFirstError()->GetMessage());
+  error.reset();
 }
 
 TEST(CommandDictionary, GetCommandsAsJson) {
   auto json_base = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': {'maximum': 100}}
+        'parameters': {'delay': {'maximum': 100}},
+        'results': {}
       },
       'shutdown': {
-        'parameters': {}
+        'parameters': {},
+        'results': {}
       }
     }
   })");
@@ -184,12 +226,14 @@
   auto json = buffet::unittests::CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': {'minimum': 10}}
+        'parameters': {'delay': {'minimum': 10}},
+        'results': {}
       }
     },
     'robot': {
       '_jump': {
-        'parameters': {'_height': 'integer'}
+        'parameters': {'_height': 'integer'},
+        'results': {}
       }
     }
   })");
diff --git a/buffet/commands/command_instance_unittest.cc b/buffet/commands/command_instance_unittest.cc
index b57de25..d5afc70 100644
--- a/buffet/commands/command_instance_unittest.cc
+++ b/buffet/commands/command_instance_unittest.cc
@@ -21,7 +21,8 @@
     auto json = CreateDictionaryValue(R"({
       'base': {
         'reboot': {
-          'parameters': {}
+          'parameters': {},
+          'results': {}
         }
       },
       'robot': {
@@ -36,7 +37,8 @@
               'type': 'string',
               'enum': ['_withAirFlip', '_withSpin', '_withKick']
             }
-          }
+          },
+          'results': {}
         },
         'speak': {
           'parameters': {
@@ -50,7 +52,8 @@
               'minimum': 0,
               'maximum': 10
             }
-          }
+          },
+          'results': {}
         }
       }
     })");
@@ -92,7 +95,8 @@
     'parameters': {
       'height': 53,
       '_jumpType': '_withKick'
-    }
+    },
+    'results': {}
   })");
   auto instance = buffet::CommandInstance::FromJson(json.get(), dict_, nullptr);
   EXPECT_EQ("robot.jump", instance->GetName());
diff --git a/buffet/commands/command_manager_unittest.cc b/buffet/commands/command_manager_unittest.cc
index 37e3716..c40f2dc 100644
--- a/buffet/commands/command_manager_unittest.cc
+++ b/buffet/commands/command_manager_unittest.cc
@@ -31,10 +31,12 @@
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       },
       'shutdown': {
-        'parameters': {}
+        'parameters': {},
+        'results': {}
       }
     }
   })");
@@ -46,10 +48,12 @@
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       },
       'shutdown': {
-        'parameters': {}
+        'parameters': {},
+        'results': {}
       }
     }
   })");
@@ -63,10 +67,12 @@
   auto json = CreateDictionaryValue(R"({
     'robot': {
       '_jump': {
-        'parameters': {'height': 'integer'}
+        'parameters': {'height': 'integer'},
+        'results': {}
       },
       '_speak': {
-        'parameters': {'phrase': 'string'}
+        'parameters': {'phrase': 'string'},
+        'results': {}
       }
     }
   })");
@@ -79,10 +85,12 @@
   auto json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       },
       'shutdown': {
-        'parameters': {}
+        'parameters': {},
+        'results': {}
       }
     }
   })");
@@ -91,12 +99,14 @@
   json = CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       }
     },
     'robot': {
       '_jump': {
-        'parameters': {'height': 'integer'}
+        'parameters': {'height': 'integer'},
+        'results': {}
       }
     }
   })");
diff --git a/buffet/commands/dbus_command_dispatcher_unittest.cc b/buffet/commands/dbus_command_dispatcher_unittest.cc
index af15c1d..ed272a1 100644
--- a/buffet/commands/dbus_command_dispatcher_unittest.cc
+++ b/buffet/commands/dbus_command_dispatcher_unittest.cc
@@ -73,10 +73,12 @@
     auto json = CreateDictionaryValue(R"({
       'base': {
         'reboot': {
-          'parameters': {'delay': 'integer'}
+          'parameters': {'delay': 'integer'},
+          'results': {}
         },
         'shutdown': {
-          'parameters': {}
+          'parameters': {},
+          'results': {}
         }
       }
     })");
diff --git a/buffet/commands/dbus_command_proxy_unittest.cc b/buffet/commands/dbus_command_proxy_unittest.cc
index 3cb907d..81d9827 100644
--- a/buffet/commands/dbus_command_proxy_unittest.cc
+++ b/buffet/commands/dbus_command_proxy_unittest.cc
@@ -50,6 +50,7 @@
     EXPECT_CALL(*bus_, AssertOnDBusThread()).Times(AnyNumber());
 
     // Command instance.
+    // TODO(antonm): Test results.
     auto json = CreateDictionaryValue(R"({
       'robot': {
         'jump': {
@@ -63,7 +64,8 @@
               'type': 'string',
               'enum': ['_withAirFlip', '_withSpin', '_withKick']
             }
-          }
+          },
+          'results': {}
         }
       }
     })");
diff --git a/buffet/commands/schema_constants.cc b/buffet/commands/schema_constants.cc
index faf58fb..a26c355 100644
--- a/buffet/commands/schema_constants.cc
+++ b/buffet/commands/schema_constants.cc
@@ -46,6 +46,7 @@
 const char kCommand_Id[] = "id";
 const char kCommand_Name[] = "name";
 const char kCommand_Parameters[] = "parameters";
+const char kCommand_Results[] = "results";
 }  // namespace attributes
 }  // namespace commands
 
diff --git a/buffet/commands/schema_constants.h b/buffet/commands/schema_constants.h
index d5a8c4e..6b06e2f 100644
--- a/buffet/commands/schema_constants.h
+++ b/buffet/commands/schema_constants.h
@@ -50,6 +50,7 @@
 extern const char kCommand_Id[];
 extern const char kCommand_Name[];
 extern const char kCommand_Parameters[];
+extern const char kCommand_Results[];
 }  // namespace attributes
 }  // namespace commands
 
diff --git a/buffet/device_registration_info_unittest.cc b/buffet/device_registration_info_unittest.cc
index 1ab5191..dd8ffbe 100644
--- a/buffet/device_registration_info_unittest.cc
+++ b/buffet/device_registration_info_unittest.cc
@@ -316,10 +316,12 @@
   auto json_base = buffet::unittests::CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': 'integer'}
+        'parameters': {'delay': 'integer'},
+        'results': {}
       },
       'shutdown': {
-        'parameters': {}
+        'parameters': {},
+        'results': {}
       }
     }
   })");
@@ -327,12 +329,14 @@
   auto json_cmds = buffet::unittests::CreateDictionaryValue(R"({
     'base': {
       'reboot': {
-        'parameters': {'delay': {'minimum': 10}}
+        'parameters': {'delay': {'minimum': 10}},
+        'results': {}
       }
     },
     'robot': {
       '_jump': {
-        'parameters': {'_height': 'integer'}
+        'parameters': {'_height': 'integer'},
+        'results': {}
       }
     }
   })");
diff --git a/buffet/etc/buffet/commands/test.json b/buffet/etc/buffet/commands/test.json
index 10f8297..f6201c7 100644
--- a/buffet/etc/buffet/commands/test.json
+++ b/buffet/etc/buffet/commands/test.json
@@ -2,11 +2,15 @@
   "base": {
     "reboot": {
       "parameters": {
+      },
+      "results": {
       }
     },
     "_jump": {
       "parameters": {
         "_height":"integer"
+      },
+      "results": {
       }
     }
   }
diff --git a/buffet/etc/buffet/gcd.json b/buffet/etc/buffet/gcd.json
index b488802..1f37cec 100644
--- a/buffet/etc/buffet/gcd.json
+++ b/buffet/etc/buffet/gcd.json
@@ -2,6 +2,8 @@
   "base": {
     "reboot": {
       "parameters": {
+      },
+      "results": {
       }
     }
   }