diff --git a/esphome/components/api/api.proto b/esphome/components/api/api.proto
index 2c9ca4a706..c1f0142017 100644
--- a/esphome/components/api/api.proto
+++ b/esphome/components/api/api.proto
@@ -308,6 +308,12 @@ enum EntityCategory {
   ENTITY_CATEGORY_DIAGNOSTIC = 2;
 }
 
+// Entity field max_data_length values match constants in esphome/core/config.py:
+//   name/object_id = 120 (NAME_MAX_LENGTH)
+//   icon = 63 (ICON_MAX_LENGTH)
+//   device_class = 47 (DEVICE_CLASS_MAX_LENGTH)
+//   unit_of_measurement = 63 (UNIT_OF_MEASUREMENT_MAX_LENGTH)
+
 // ==================== BINARY SENSOR ====================
 message ListEntitiesBinarySensorResponse {
   option (id) = 12;
@@ -315,15 +321,15 @@ message ListEntitiesBinarySensorResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_BINARY_SENSOR";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string device_class = 5;
+  string device_class = 5 [(max_data_length) = 47];
   bool is_status_binary_sensor = 6;
   bool disabled_by_default = 7;
-  string icon = 8 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 8 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   EntityCategory entity_category = 9;
   uint32 device_id = 10 [(field_ifdef) = "USE_DEVICES"];
 }
@@ -349,17 +355,17 @@ message ListEntitiesCoverResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_COVER";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
   bool assumed_state = 5;
   bool supports_position = 6;
   bool supports_tilt = 7;
-  string device_class = 8;
+  string device_class = 8 [(max_data_length) = 47];
   bool disabled_by_default = 9;
-  string icon = 10 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 10 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   EntityCategory entity_category = 11;
   bool supports_stop = 12;
   uint32 device_id = 13 [(field_ifdef) = "USE_DEVICES"];
@@ -433,9 +439,9 @@ message ListEntitiesFanResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_FAN";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
   bool supports_oscillation = 5;
@@ -443,7 +449,7 @@ message ListEntitiesFanResponse {
   bool supports_direction = 7;
   int32 supported_speed_count = 8;
   bool disabled_by_default = 9;
-  string icon = 10 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 10 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   EntityCategory entity_category = 11;
   repeated string supported_preset_modes = 12 [(container_pointer_no_template) = "std::vector<const char *>"];
   uint32 device_id = 13 [(field_ifdef) = "USE_DEVICES"];
@@ -521,9 +527,9 @@ message ListEntitiesLightResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_LIGHT";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
   repeated ColorMode supported_color_modes = 12 [(container_pointer_no_template) = "light::ColorModeMask"];
@@ -540,7 +546,7 @@ message ListEntitiesLightResponse {
   float max_mireds = 10;
   repeated string effects = 11 [(container_pointer_no_template) = "FixedVector<const char *>"];
   bool disabled_by_default = 13;
-  string icon = 14 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 14 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   EntityCategory entity_category = 15;
   uint32 device_id = 16 [(field_ifdef) = "USE_DEVICES"];
 }
@@ -626,16 +632,16 @@ message ListEntitiesSensorResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_SENSOR";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
-  string unit_of_measurement = 6;
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
+  string unit_of_measurement = 6 [(max_data_length) = 63];
   int32 accuracy_decimals = 7;
   bool force_update = 8;
-  string device_class = 9;
+  string device_class = 9 [(max_data_length) = 47];
   SensorStateClass state_class = 10;
   // Last reset type removed in 2021.9.0
   // Deprecated in API version 1.5
@@ -666,16 +672,16 @@ message ListEntitiesSwitchResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_SWITCH";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool assumed_state = 6;
   bool disabled_by_default = 7;
   EntityCategory entity_category = 8;
-  string device_class = 9;
+  string device_class = 9 [(max_data_length) = 47];
   uint32 device_id = 10 [(field_ifdef) = "USE_DEVICES"];
 }
 message SwitchStateResponse {
@@ -708,15 +714,15 @@ message ListEntitiesTextSensorResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_TEXT_SENSOR";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
-  string device_class = 8;
+  string device_class = 8 [(max_data_length) = 47];
   uint32 device_id = 9 [(field_ifdef) = "USE_DEVICES"];
 }
 message TextSensorStateResponse {
@@ -971,12 +977,12 @@ message ListEntitiesCameraResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_CAMERA";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
   bool disabled_by_default = 5;
-  string icon = 6 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 6 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   EntityCategory entity_category = 7;
   uint32 device_id = 8 [(field_ifdef) = "USE_DEVICES"];
 }
@@ -1056,9 +1062,9 @@ message ListEntitiesClimateResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_CLIMATE";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
   bool supports_current_temperature = 5; // Deprecated: use feature_flags
@@ -1078,7 +1084,7 @@ message ListEntitiesClimateResponse {
   repeated ClimatePreset supported_presets = 16 [(container_pointer_no_template) = "climate::ClimatePresetMask"];
   repeated string supported_custom_presets = 17 [(container_pointer_no_template) = "std::vector<const char *>"];
   bool disabled_by_default = 18;
-  string icon = 19 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 19 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   EntityCategory entity_category = 20;
   float visual_current_temperature_step = 21;
   bool supports_current_humidity = 22; // Deprecated: use feature_flags
@@ -1167,10 +1173,10 @@ message ListEntitiesWaterHeaterResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_WATER_HEATER";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
-  string icon = 4 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string name = 3 [(max_data_length) = 120, (force) = true];
+  string icon = 4 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 5;
   EntityCategory entity_category = 6;
   uint32 device_id = 7 [(field_ifdef) = "USE_DEVICES"];
@@ -1243,12 +1249,12 @@ message ListEntitiesNumberResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_NUMBER";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   float min_value = 6;
   float max_value = 7;
   float step = 8;
@@ -1256,7 +1262,7 @@ message ListEntitiesNumberResponse {
   EntityCategory entity_category = 10;
   string unit_of_measurement = 11;
   NumberMode mode = 12;
-  string device_class = 13;
+  string device_class = 13 [(max_data_length) = 47];
   uint32 device_id = 14 [(field_ifdef) = "USE_DEVICES"];
 }
 message NumberStateResponse {
@@ -1292,12 +1298,12 @@ message ListEntitiesSelectResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_SELECT";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   repeated string options = 6 [(container_pointer_no_template) = "FixedVector<const char *>"];
   bool disabled_by_default = 7;
   EntityCategory entity_category = 8;
@@ -1336,12 +1342,12 @@ message ListEntitiesSirenResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_SIREN";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   repeated string tones = 7 [(container_pointer_no_template) = "FixedVector<const char *>"];
   bool supports_duration = 8;
@@ -1399,12 +1405,12 @@ message ListEntitiesLockResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_LOCK";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
   bool assumed_state = 8;
@@ -1448,15 +1454,15 @@ message ListEntitiesButtonResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_BUTTON";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
-  string device_class = 8;
+  string device_class = 8 [(max_data_length) = 47];
   uint32 device_id = 9 [(field_ifdef) = "USE_DEVICES"];
 }
 message ButtonCommandRequest {
@@ -1515,12 +1521,12 @@ message ListEntitiesMediaPlayerResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_MEDIA_PLAYER";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
 
@@ -2103,11 +2109,11 @@ message ListEntitiesAlarmControlPanelResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_ALARM_CONTROL_PANEL";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
   uint32 supported_features = 8;
@@ -2150,11 +2156,11 @@ message ListEntitiesTextResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_TEXT";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
 
@@ -2198,12 +2204,12 @@ message ListEntitiesDateResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_DATETIME_DATE";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
   uint32 device_id = 8 [(field_ifdef) = "USE_DEVICES"];
@@ -2245,12 +2251,12 @@ message ListEntitiesTimeResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_DATETIME_TIME";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
   uint32 device_id = 8 [(field_ifdef) = "USE_DEVICES"];
@@ -2292,15 +2298,15 @@ message ListEntitiesEventResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_EVENT";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
-  string device_class = 8;
+  string device_class = 8 [(max_data_length) = 47];
 
   repeated string event_types = 9 [(container_pointer_no_template) = "FixedVector<const char *>"];
   uint32 device_id = 10 [(field_ifdef) = "USE_DEVICES"];
@@ -2323,15 +2329,15 @@ message ListEntitiesValveResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_VALVE";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
-  string device_class = 8;
+  string device_class = 8 [(max_data_length) = 47];
 
   bool assumed_state = 9;
   bool supports_position = 10;
@@ -2378,12 +2384,12 @@ message ListEntitiesDateTimeResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_DATETIME_DATETIME";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
   uint32 device_id = 8 [(field_ifdef) = "USE_DEVICES"];
@@ -2421,15 +2427,15 @@ message ListEntitiesUpdateResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_UPDATE";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
+  string name = 3 [(max_data_length) = 120, (force) = true];
   reserved 4; // Deprecated: was string unique_id
 
-  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string icon = 5 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 6;
   EntityCategory entity_category = 7;
-  string device_class = 8;
+  string device_class = 8 [(max_data_length) = 47];
   uint32 device_id = 9 [(field_ifdef) = "USE_DEVICES"];
 }
 message UpdateStateResponse {
@@ -2504,10 +2510,10 @@ message ListEntitiesInfraredResponse {
   option (source) = SOURCE_SERVER;
   option (ifdef) = "USE_INFRARED";
 
-  string object_id = 1;
+  string object_id = 1 [(max_data_length) = 120, (force) = true];
   fixed32 key = 2 [(force) = true];
-  string name = 3;
-  string icon = 4 [(field_ifdef) = "USE_ENTITY_ICON"];
+  string name = 3 [(max_data_length) = 120, (force) = true];
+  string icon = 4 [(field_ifdef) = "USE_ENTITY_ICON", (max_data_length) = 63];
   bool disabled_by_default = 5;
   EntityCategory entity_category = 6;
   uint32 device_id = 7 [(field_ifdef) = "USE_DEVICES"];
diff --git a/esphome/components/api/api_options.proto b/esphome/components/api/api_options.proto
index 0aa9e814cf..0f71268d70 100644
--- a/esphome/components/api/api_options.proto
+++ b/esphome/components/api/api_options.proto
@@ -102,4 +102,10 @@ extend google.protobuf.FieldOptions {
     // and direct byte writes instead of varint branching, since the encoded varint
     // is guaranteed to be 1 byte.
     optional uint32 max_value = 50017;
+
+    // max_data_length: Maximum length of a string or bytes field.
+    // When max_data_length < 128, the code generator emits constant-size
+    // length varint calculations and direct byte writes, since the length
+    // varint is guaranteed to be 1 byte.
+    optional uint32 max_data_length = 50018;
 }
diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index f4e2fc5594..98bea30628 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -207,9 +207,9 @@ uint32_t DeviceInfoResponse::calculate_size() const {
 }
 #ifdef USE_BINARY_SENSOR
 void ListEntitiesBinarySensorResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
   buffer.encode_string(5, this->device_class);
   buffer.encode_bool(6, this->is_status_binary_sensor);
   buffer.encode_bool(7, this->disabled_by_default);
@@ -223,14 +223,14 @@ void ListEntitiesBinarySensorResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesBinarySensorResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += 2 + this->name.size();
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
   size += ProtoSize::calc_bool(1, this->is_status_binary_sensor);
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
 #ifdef USE_DEVICES
@@ -259,9 +259,9 @@ uint32_t BinarySensorStateResponse::calculate_size() const {
 #endif
 #ifdef USE_COVER
 void ListEntitiesCoverResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
   buffer.encode_bool(5, this->assumed_state);
   buffer.encode_bool(6, this->supports_position);
   buffer.encode_bool(7, this->supports_tilt);
@@ -278,16 +278,16 @@ void ListEntitiesCoverResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesCoverResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   size += ProtoSize::calc_bool(1, this->assumed_state);
   size += ProtoSize::calc_bool(1, this->supports_position);
   size += ProtoSize::calc_bool(1, this->supports_tilt);
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
   size += ProtoSize::calc_bool(1, this->supports_stop);
@@ -356,9 +356,9 @@ bool CoverCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_FAN
 void ListEntitiesFanResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
   buffer.encode_bool(5, this->supports_oscillation);
   buffer.encode_bool(6, this->supports_speed);
   buffer.encode_bool(7, this->supports_direction);
@@ -377,16 +377,16 @@ void ListEntitiesFanResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesFanResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   size += ProtoSize::calc_bool(1, this->supports_oscillation);
   size += ProtoSize::calc_bool(1, this->supports_speed);
   size += ProtoSize::calc_bool(1, this->supports_direction);
   size += ProtoSize::calc_int32(1, this->supported_speed_count);
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
   if (!this->supported_preset_modes->empty()) {
@@ -486,9 +486,9 @@ bool FanCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_LIGHT
 void ListEntitiesLightResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
   for (const auto &it : *this->supported_color_modes) {
     buffer.encode_uint32(12, static_cast<uint32_t>(it), true);
   }
@@ -508,9 +508,9 @@ void ListEntitiesLightResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesLightResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   if (!this->supported_color_modes->empty()) {
     for (const auto &it : *this->supported_color_modes) {
       size += ProtoSize::calc_uint32_force(1, static_cast<uint32_t>(it));
@@ -525,7 +525,7 @@ uint32_t ListEntitiesLightResponse::calculate_size() const {
   }
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
 #ifdef USE_DEVICES
@@ -682,9 +682,9 @@ bool LightCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_SENSOR
 void ListEntitiesSensorResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -701,16 +701,16 @@ void ListEntitiesSensorResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesSensorResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
-  size += ProtoSize::calc_length(1, this->unit_of_measurement.size());
+  size += !this->unit_of_measurement.empty() ? 2 + this->unit_of_measurement.size() : 0;
   size += ProtoSize::calc_int32(1, this->accuracy_decimals);
   size += ProtoSize::calc_bool(1, this->force_update);
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->state_class));
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -740,9 +740,9 @@ uint32_t SensorStateResponse::calculate_size() const {
 #endif
 #ifdef USE_SWITCH
 void ListEntitiesSwitchResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -756,16 +756,16 @@ void ListEntitiesSwitchResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesSwitchResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->assumed_state);
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
 #ifdef USE_DEVICES
   size += ProtoSize::calc_uint32(1, this->device_id);
 #endif
@@ -815,9 +815,9 @@ bool SwitchCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_TEXT_SENSOR
 void ListEntitiesTextSensorResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -830,15 +830,15 @@ void ListEntitiesTextSensorResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesTextSensorResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
 #ifdef USE_DEVICES
   size += ProtoSize::calc_uint32(1, this->device_id);
 #endif
@@ -1264,9 +1264,9 @@ uint32_t ExecuteServiceResponse::calculate_size() const {
 #endif
 #ifdef USE_CAMERA
 void ListEntitiesCameraResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
   buffer.encode_bool(5, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(6, this->icon);
@@ -1278,12 +1278,12 @@ void ListEntitiesCameraResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesCameraResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
 #ifdef USE_DEVICES
@@ -1325,9 +1325,9 @@ bool CameraImageRequest::decode_varint(uint32_t field_id, proto_varint_value_t v
 #endif
 #ifdef USE_CLIMATE
 void ListEntitiesClimateResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
   buffer.encode_bool(5, this->supports_current_temperature);
   buffer.encode_bool(6, this->supports_two_point_target_temperature);
   for (const auto &it : *this->supported_modes) {
@@ -1369,9 +1369,9 @@ void ListEntitiesClimateResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesClimateResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   size += ProtoSize::calc_bool(1, this->supports_current_temperature);
   size += ProtoSize::calc_bool(1, this->supports_two_point_target_temperature);
   if (!this->supported_modes->empty()) {
@@ -1410,7 +1410,7 @@ uint32_t ListEntitiesClimateResponse::calculate_size() const {
   }
   size += ProtoSize::calc_bool(2, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(2, this->icon.size());
+  size += !this->icon.empty() ? 3 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(2, static_cast<uint32_t>(this->entity_category));
   size += ProtoSize::calc_float(2, this->visual_current_temperature_step);
@@ -1558,9 +1558,9 @@ bool ClimateCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_WATER_HEATER
 void ListEntitiesWaterHeaterResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(4, this->icon);
 #endif
@@ -1579,11 +1579,11 @@ void ListEntitiesWaterHeaterResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesWaterHeaterResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -1670,9 +1670,9 @@ bool WaterHeaterCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value
 #endif
 #ifdef USE_NUMBER
 void ListEntitiesNumberResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -1690,11 +1690,11 @@ void ListEntitiesNumberResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesNumberResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_float(1, this->min_value);
   size += ProtoSize::calc_float(1, this->max_value);
@@ -1703,7 +1703,7 @@ uint32_t ListEntitiesNumberResponse::calculate_size() const {
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
   size += ProtoSize::calc_length(1, this->unit_of_measurement.size());
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->mode));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
 #ifdef USE_DEVICES
   size += ProtoSize::calc_uint32(1, this->device_id);
 #endif
@@ -1755,9 +1755,9 @@ bool NumberCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_SELECT
 void ListEntitiesSelectResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -1772,11 +1772,11 @@ void ListEntitiesSelectResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesSelectResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   if (!this->options->empty()) {
     for (const char *it : *this->options) {
@@ -1844,9 +1844,9 @@ bool SelectCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_SIREN
 void ListEntitiesSirenResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -1863,11 +1863,11 @@ void ListEntitiesSirenResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesSirenResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   if (!this->tones->empty()) {
@@ -1956,9 +1956,9 @@ bool SirenCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_LOCK
 void ListEntitiesLockResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -1974,11 +1974,11 @@ void ListEntitiesLockResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesLockResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -2049,9 +2049,9 @@ bool LockCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_BUTTON
 void ListEntitiesButtonResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -2064,15 +2064,15 @@ void ListEntitiesButtonResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesButtonResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
 #ifdef USE_DEVICES
   size += ProtoSize::calc_uint32(1, this->device_id);
 #endif
@@ -2119,9 +2119,9 @@ uint32_t MediaPlayerSupportedFormat::calculate_size() const {
   return size;
 }
 void ListEntitiesMediaPlayerResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -2138,11 +2138,11 @@ void ListEntitiesMediaPlayerResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesMediaPlayerResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -2941,9 +2941,9 @@ bool VoiceAssistantSetConfiguration::decode_length(uint32_t field_id, ProtoLengt
 #endif
 #ifdef USE_ALARM_CONTROL_PANEL
 void ListEntitiesAlarmControlPanelResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -2958,11 +2958,11 @@ void ListEntitiesAlarmControlPanelResponse::encode(ProtoWriteBuffer &buffer) con
 }
 uint32_t ListEntitiesAlarmControlPanelResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3029,9 +3029,9 @@ bool AlarmControlPanelCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit
 #endif
 #ifdef USE_TEXT
 void ListEntitiesTextResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3047,11 +3047,11 @@ void ListEntitiesTextResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesTextResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3118,9 +3118,9 @@ bool TextCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_DATETIME_DATE
 void ListEntitiesDateResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3132,11 +3132,11 @@ void ListEntitiesDateResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesDateResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3201,9 +3201,9 @@ bool DateCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_DATETIME_TIME
 void ListEntitiesTimeResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3215,11 +3215,11 @@ void ListEntitiesTimeResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesTimeResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3284,9 +3284,9 @@ bool TimeCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_EVENT
 void ListEntitiesEventResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3302,15 +3302,15 @@ void ListEntitiesEventResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesEventResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
   if (!this->event_types->empty()) {
     for (const char *it : *this->event_types) {
       size += ProtoSize::calc_length_force(1, strlen(it));
@@ -3340,9 +3340,9 @@ uint32_t EventResponse::calculate_size() const {
 #endif
 #ifdef USE_VALVE
 void ListEntitiesValveResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3358,15 +3358,15 @@ void ListEntitiesValveResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesValveResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
   size += ProtoSize::calc_bool(1, this->assumed_state);
   size += ProtoSize::calc_bool(1, this->supports_position);
   size += ProtoSize::calc_bool(1, this->supports_stop);
@@ -3427,9 +3427,9 @@ bool ValveCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_DATETIME_DATETIME
 void ListEntitiesDateTimeResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3441,11 +3441,11 @@ void ListEntitiesDateTimeResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesDateTimeResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3500,9 +3500,9 @@ bool DateTimeCommandRequest::decode_32bit(uint32_t field_id, Proto32Bit value) {
 #endif
 #ifdef USE_UPDATE
 void ListEntitiesUpdateResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(5, this->icon);
 #endif
@@ -3515,15 +3515,15 @@ void ListEntitiesUpdateResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesUpdateResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
-  size += ProtoSize::calc_length(1, this->device_class.size());
+  size += !this->device_class.empty() ? 2 + this->device_class.size() : 0;
 #ifdef USE_DEVICES
   size += ProtoSize::calc_uint32(1, this->device_id);
 #endif
@@ -3641,9 +3641,9 @@ uint32_t ZWaveProxyRequest::calculate_size() const {
 #endif
 #ifdef USE_INFRARED
 void ListEntitiesInfraredResponse::encode(ProtoWriteBuffer &buffer) const {
-  buffer.encode_string(1, this->object_id);
+  buffer.write_short_string(10, this->object_id);
   buffer.write_tag_and_fixed32(21, this->key);
-  buffer.encode_string(3, this->name);
+  buffer.write_short_string(26, this->name);
 #ifdef USE_ENTITY_ICON
   buffer.encode_string(4, this->icon);
 #endif
@@ -3657,11 +3657,11 @@ void ListEntitiesInfraredResponse::encode(ProtoWriteBuffer &buffer) const {
 }
 uint32_t ListEntitiesInfraredResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->object_id.size());
+  size += 2 + this->object_id.size();
   size += 5;
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += ProtoSize::calc_length(1, this->icon.size());
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
diff --git a/esphome/components/api/proto.h b/esphome/components/api/proto.h
index a3b274df80..4cb5f04fe4 100644
--- a/esphome/components/api/proto.h
+++ b/esphome/components/api/proto.h
@@ -280,6 +280,16 @@ class ProtoWriteBuffer {
     std::memcpy(pos, data, len);
     this->pos_ = pos + len;
   }
+  /// Write tag + 1-byte length + raw string data. For strings with max_data_length < 128.
+  /// Tag must be a single-byte varint (< 128). Always encodes (no zero check).
+  inline void write_short_string(uint8_t tag, const StringRef &ref) ESPHOME_ALWAYS_INLINE {
+    this->debug_check_bounds_(2 + ref.size());
+    uint8_t *__restrict__ pos = this->pos_;
+    *pos++ = tag;
+    *pos++ = static_cast<uint8_t>(ref.size());
+    std::memcpy(pos, ref.c_str(), ref.size());
+    this->pos_ = pos + ref.size();
+  }
   /// Write a precomputed tag byte + 32-bit value in one operation.
   /// Tag must be a single-byte varint (< 128). No zero check.
   inline void write_tag_and_fixed32(uint8_t tag, uint32_t value) ESPHOME_ALWAYS_INLINE {
diff --git a/esphome/components/number/__init__.py b/esphome/components/number/__init__.py
index 90f9fe1835..26d2602ba4 100644
--- a/esphome/components/number/__init__.py
+++ b/esphome/components/number/__init__.py
@@ -79,6 +79,7 @@ from esphome.const import (
     DEVICE_CLASS_WIND_SPEED,
 )
 from esphome.core import CORE, CoroPriority, coroutine_with_priority
+from esphome.core.config import UNIT_OF_MEASUREMENT_MAX_LENGTH
 from esphome.core.entity_helpers import (
     entity_duplicate_validator,
     setup_device_class,
@@ -186,7 +187,11 @@ NUMBER_OPERATION_OPTIONS = {
 }
 
 validate_device_class = cv.one_of(*DEVICE_CLASSES, lower=True, space="_")
-validate_unit_of_measurement = cv.string_strict
+validate_unit_of_measurement = cv.All(
+    cv.string_strict,
+    # Keep in sync with max_data_length in api.proto
+    cv.Length(max=UNIT_OF_MEASUREMENT_MAX_LENGTH),
+)
 
 _NUMBER_SCHEMA = (
     cv.ENTITY_BASE_SCHEMA.extend(web_server.WEBSERVER_SORTING_SCHEMA)
diff --git a/esphome/components/sensor/__init__.py b/esphome/components/sensor/__init__.py
index 626466eefa..275c4542fb 100644
--- a/esphome/components/sensor/__init__.py
+++ b/esphome/components/sensor/__init__.py
@@ -106,6 +106,7 @@ from esphome.const import (
     ENTITY_CATEGORY_CONFIG,
 )
 from esphome.core import CORE, CoroPriority, coroutine_with_priority
+from esphome.core.config import UNIT_OF_MEASUREMENT_MAX_LENGTH
 from esphome.core.entity_helpers import (
     entity_duplicate_validator,
     setup_device_class,
@@ -290,7 +291,11 @@ ClampFilter = sensor_ns.class_("ClampFilter", Filter)
 RoundFilter = sensor_ns.class_("RoundFilter", Filter)
 RoundMultipleFilter = sensor_ns.class_("RoundMultipleFilter", Filter)
 
-validate_unit_of_measurement = cv.string_strict
+validate_unit_of_measurement = cv.All(
+    cv.string_strict,
+    # Keep in sync with max_data_length in api.proto
+    cv.Length(max=UNIT_OF_MEASUREMENT_MAX_LENGTH),
+)
 validate_accuracy_decimals = cv.int_
 validate_icon = cv.icon
 validate_device_class = cv.one_of(*DEVICE_CLASSES, lower=True, space="_")
diff --git a/esphome/core/config.py b/esphome/core/config.py
index c47693c783..675b9296e5 100644
--- a/esphome/core/config.py
+++ b/esphome/core/config.py
@@ -233,6 +233,9 @@ DEVICE_CLASS_MAX_LENGTH = 47
 # Keep in sync with MAX_ICON_LENGTH in esphome/core/entity_base.h
 ICON_MAX_LENGTH = 63
 
+# Max unit of measurement string length
+UNIT_OF_MEASUREMENT_MAX_LENGTH = 63
+
 AREA_SCHEMA = cv.Schema(
     {
         cv.GenerateID(CONF_ID): cv.declare_id(Area),
diff --git a/esphome/core/entity_helpers.py b/esphome/core/entity_helpers.py
index 0589b92364..fc931c2baa 100644
--- a/esphome/core/entity_helpers.py
+++ b/esphome/core/entity_helpers.py
@@ -17,7 +17,11 @@ from esphome.const import (
     CONF_UNIT_OF_MEASUREMENT,
 )
 from esphome.core import CORE, ID, CoroPriority, coroutine_with_priority
-from esphome.core.config import DEVICE_CLASS_MAX_LENGTH, ICON_MAX_LENGTH
+from esphome.core.config import (
+    DEVICE_CLASS_MAX_LENGTH,
+    ICON_MAX_LENGTH,
+    UNIT_OF_MEASUREMENT_MAX_LENGTH,
+)
 from esphome.cpp_generator import MockObj, RawStatement, add, get_variable
 import esphome.final_validate as fv
 from esphome.helpers import cpp_string_escape, fnv1_hash_object_id, sanitize, snake_case
@@ -200,6 +204,11 @@ def register_device_class(value: str) -> int:
 
 def register_unit_of_measurement(value: str) -> int:
     """Register a unit_of_measurement string and return its 1-based index."""
+    if value and len(value) > UNIT_OF_MEASUREMENT_MAX_LENGTH:
+        raise ValueError(
+            f"Unit of measurement string too long ({len(value)} chars, "
+            f"max {UNIT_OF_MEASUREMENT_MAX_LENGTH}): '{value}'"
+        )
     return _register_string(value, _get_pool().units, _MAX_UNITS, "unit_of_measurement")
 
 
diff --git a/script/api_protobuf/api_protobuf.py b/script/api_protobuf/api_protobuf.py
index 34fe9f5bf9..260c696dc0 100755
--- a/script/api_protobuf/api_protobuf.py
+++ b/script/api_protobuf/api_protobuf.py
@@ -161,6 +161,11 @@ class TypeInfo(ABC):
         """Get the max_value option for this field, or None if not set."""
         return get_field_opt(self._field, pb.max_value, None)
 
+    @property
+    def max_data_length(self) -> int | None:
+        """Get the max_data_length option for this field, or None if not set."""
+        return get_field_opt(self._field, pb.max_data_length, None)
+
     @property
     def wire_type(self) -> WireType:
         """Get the wire type for the field."""
@@ -371,7 +376,11 @@ class TypeInfo(ABC):
         return f"size += ProtoSize::{method}({field_id_size}, {value});"
 
     def _get_single_byte_varint_size(
-        self, name: str, force: bool, extra_expr: str | None = None
+        self,
+        name: str,
+        force: bool,
+        extra_expr: str | None = None,
+        zero_check: str | None = None,
     ) -> str:
         """Size calculation when the varint is guaranteed to be 1 byte.
 
@@ -382,12 +391,14 @@ class TypeInfo(ABC):
             name: Expression to check for zero (non-force only)
             force: Whether to skip the zero check
             extra_expr: Additional variable expression to add (e.g., data length)
+            zero_check: Override expression for the zero check (e.g., "!x.empty()")
         """
         fixed = self.calculate_field_id_size() + 1
         size_expr = f"{fixed} + {extra_expr}" if extra_expr else str(fixed)
         if force:
             return f"size += {size_expr};"
-        return f"size += {name} ? {size_expr} : 0;"
+        check = zero_check or name
+        return f"size += {check} ? {size_expr} : 0;"
 
     @abstractmethod
     def get_size_calculation(self, name: str, force: bool = False) -> str:
@@ -1063,8 +1074,14 @@ class PointerToStringBufferType(PointerToBufferTypeBase):
 
     @property
     def encode_content(self) -> str:
+        max_len = self.max_data_length
+        if max_len is not None and max_len < 128 and self.force:
+            tag = self.calculate_tag()
+            if tag < 128:
+                return f"buffer.write_short_string({tag}, this->{self.field_name});"
         if result := self._encode_bytes_with_precomputed_tag(
-            f"this->{self.field_name}.c_str()", f"this->{self.field_name}.size()"
+            f"this->{self.field_name}.c_str()",
+            f"this->{self.field_name}.size()",
         ):
             return result
         if self.force:
@@ -1089,7 +1106,16 @@ class PointerToStringBufferType(PointerToBufferTypeBase):
         return f'dump_field(out, ESPHOME_PSTR("{self.name}"), this->{self.field_name});'
 
     def get_size_calculation(self, name: str, force: bool = False) -> str:
-        return f"size += ProtoSize::calc_length({self.calculate_field_id_size()}, this->{self.field_name}.size());"
+        size_field = f"this->{self.field_name}.size()"
+        max_len = self.max_data_length
+        if max_len is not None and max_len < 128:
+            return self._get_single_byte_varint_size(
+                size_field,
+                force,
+                extra_expr=size_field,
+                zero_check=f"!this->{self.field_name}.empty()",
+            )
+        return self._get_simple_size_calculation(size_field, force, "length")
 
     def get_estimated_size(self) -> int:
         return self.calculate_field_id_size() + 8  # field ID + 8 bytes typical string
diff --git a/tests/unit_tests/core/test_entity_helpers.py b/tests/unit_tests/core/test_entity_helpers.py
index d6cbb8c6be..e79ff850f9 100644
--- a/tests/unit_tests/core/test_entity_helpers.py
+++ b/tests/unit_tests/core/test_entity_helpers.py
@@ -28,6 +28,7 @@ from esphome.core.entity_helpers import (
     get_base_entity_object_id,
     register_device_class,
     register_icon,
+    register_unit_of_measurement,
     setup_device_class,
     setup_entity,
     setup_unit_of_measurement,
@@ -925,6 +926,22 @@ def test_register_device_class_max_length() -> None:
     assert register_device_class("") == 0
 
 
+def test_register_unit_of_measurement_max_length() -> None:
+    """Test register_unit_of_measurement rejects units exceeding 63 characters."""
+    # 63 chars should succeed
+    max_uom = "a" * 63
+    idx = register_unit_of_measurement(max_uom)
+    assert idx > 0
+
+    # 64 chars should fail
+    too_long = "a" * 64
+    with pytest.raises(ValueError, match="Unit of measurement string too long"):
+        register_unit_of_measurement(too_long)
+
+    # Empty string returns 0
+    assert register_unit_of_measurement("") == 0
+
+
 @pytest.mark.asyncio
 async def test_setup_entity_with_entity_category(
     setup_test_environment: list[str],