diff --git a/esphome/components/api/api.proto b/esphome/components/api/api.proto
index 07705baff6..8e3b5a1ffb 100644
--- a/esphome/components/api/api.proto
+++ b/esphome/components/api/api.proto
@@ -129,11 +129,12 @@ message HelloResponse {
 
   // A string identifying the server (ESP); like client info this may be empty
   // and only exists for debugging/logging purposes.
-  // For example "ESPHome v1.10.0 on ESP8266"
-  string server_info = 3;
+  // Currently set to ESPHOME_VERSION string literal.
+  string server_info = 3 [(max_data_length) = 32, (force) = true];
 
   // The name of the server (App.get_name())
-  string name = 4;
+  // max_data_length matches config_validation.NAME_MAX_LENGTH
+  string name = 4 [(max_data_length) = 120, (force) = true];
 }
 
 // DEPRECATED in ESPHome 2026.1.0 - Password authentication is no longer supported.
@@ -196,12 +197,14 @@ message DeviceInfoRequest {
 
 message AreaInfo {
   uint32 area_id = 1;
-  string name = 2;
+  // max_data_length matches core/config.FRIENDLY_NAME_MAX_LEN via AREA_SCHEMA
+  string name = 2 [(max_data_length) = 120, (force) = true];
 }
 
 message DeviceInfo {
   uint32 device_id = 1;
-  string name = 2;
+  // max_data_length matches core/config.FRIENDLY_NAME_MAX_LEN via DEVICE_SCHEMA
+  string name = 2 [(max_data_length) = 120, (force) = true];
   uint32 area_id = 3;
 }
 
@@ -216,6 +219,12 @@ message SerialProxyInfo {
   SerialProxyPortType port_type = 2;  // Port type (RS232, RS485)
 }
 
+// DeviceInfoResponse max_data_length values:
+//   name/friendly_name = 120 (config_validation.NAME_MAX_LENGTH / core/config.FRIENDLY_NAME_MAX_LEN)
+//   mac_address/bluetooth_mac_address = 17 (MAC_ADDRESS_PRETTY_BUFFER_SIZE - 1, constexpr)
+//   esphome_version = 32 (ESPHOME_VERSION string literal)
+//   compilation_time = 25 (Application::BUILD_TIME_STR_SIZE - 1, constexpr)
+//   manufacturer = 20 (longest hardcoded literal: "Nordic Semiconductor")
 message DeviceInfoResponse {
   option (id) = 10;
   option (source) = SOURCE_SERVER;
@@ -225,18 +234,18 @@ message DeviceInfoResponse {
   bool uses_password = 1 [deprecated = true];
 
   // The name of the node, given by "App.set_name()"
-  string name = 2;
+  string name = 2 [(max_data_length) = 120, (force) = true];
 
   // The mac address of the device. For example "AC:BC:32:89:0E:A9"
-  string mac_address = 3;
+  string mac_address = 3 [(max_data_length) = 17, (force) = true];
 
   // A string describing the ESPHome version. For example "1.10.0"
-  string esphome_version = 4;
+  string esphome_version = 4 [(max_data_length) = 32, (force) = true];
 
   // A string describing the date of compilation, this is generated by the compiler
   // and therefore may not be in the same format all the time.
   // If the user isn't using ESPHome, this will also not be set.
-  string compilation_time = 5;
+  string compilation_time = 5 [(max_data_length) = 25, (force) = true];
 
   // The model of the board. For example NodeMCU
   string model = 6;
@@ -253,9 +262,9 @@ message DeviceInfoResponse {
   uint32 legacy_bluetooth_proxy_version = 11 [deprecated=true, (field_ifdef) = "USE_BLUETOOTH_PROXY"];
   uint32 bluetooth_proxy_feature_flags = 15 [(field_ifdef) = "USE_BLUETOOTH_PROXY"];
 
-  string manufacturer = 12;
+  string manufacturer = 12 [(max_data_length) = 20, (force) = true];
 
-  string friendly_name = 13;
+  string friendly_name = 13 [(max_data_length) = 120, (force) = true];
 
   // Deprecated in API version 1.10
   uint32 legacy_voice_assistant_version = 14 [deprecated=true, (field_ifdef) = "USE_VOICE_ASSISTANT"];
@@ -264,7 +273,7 @@ message DeviceInfoResponse {
   string suggested_area = 16 [(field_ifdef) = "USE_AREAS"];
 
   // The Bluetooth mac address of the device. For example "AC:BC:32:89:0E:AA"
-  string bluetooth_mac_address = 18 [(field_ifdef) = "USE_BLUETOOTH_PROXY"];
+  string bluetooth_mac_address = 18 [(max_data_length) = 17, (force) = true, (field_ifdef) = "USE_BLUETOOTH_PROXY"];
 
   // Supports receiving and saving api encryption key
   bool api_encryption_supported = 19 [(field_ifdef) = "USE_API_NOISE"];
diff --git a/esphome/components/api/api_connection.cpp b/esphome/components/api/api_connection.cpp
index feb16e4f4c..53c4aabcb7 100644
--- a/esphome/components/api/api_connection.cpp
+++ b/esphome/components/api/api_connection.cpp
@@ -72,6 +72,12 @@ static constexpr uint32_t HANDSHAKE_TIMEOUT_MS = 60000;
 
 static constexpr auto ESPHOME_VERSION_REF = StringRef::from_lit(ESPHOME_VERSION);
 
+// Cross-validate C++ constants against proto max_data_length annotations in api.proto
+static_assert(MAC_ADDRESS_PRETTY_BUFFER_SIZE - 1 == 17,
+              "Update max_data_length for mac_address/bluetooth_mac_address in api.proto");
+static_assert(Application::BUILD_TIME_STR_SIZE - 1 == 25, "Update max_data_length for compilation_time in api.proto");
+static_assert(sizeof(ESPHOME_VERSION) - 1 <= 32, "Update max_data_length for esphome_version in api.proto");
+
 static const char *const TAG = "api.connection";
 #ifdef USE_CAMERA
 static const int CAMERA_STOP_STREAM = 5000;
@@ -1716,6 +1722,7 @@ bool APIConnection::send_device_info_response_() {
   static constexpr auto MANUFACTURER = StringRef::from_lit(ESPHOME_MANUFACTURER);
   resp.manufacturer = MANUFACTURER;
 #endif
+  static_assert(sizeof(ESPHOME_MANUFACTURER) - 1 <= 20, "Update max_data_length for manufacturer in api.proto");
 #undef ESPHOME_MANUFACTURER
 
 #ifdef USE_ESP8266
diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index f7c68b95a7..66996452fa 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -35,29 +35,29 @@ uint8_t *HelloResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM
   uint8_t *__restrict__ pos = buffer.get_pos();
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 1, this->api_version_major);
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 2, this->api_version_minor);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 3, this->server_info);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 4, this->name);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 26, this->server_info);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 34, this->name);
   return pos;
 }
 uint32_t HelloResponse::calculate_size() const {
   uint32_t size = 0;
   size += ProtoSize::calc_uint32(1, this->api_version_major);
   size += ProtoSize::calc_uint32(1, this->api_version_minor);
-  size += ProtoSize::calc_length(1, this->server_info.size());
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->server_info.size();
+  size += 2 + this->name.size();
   return size;
 }
 #ifdef USE_AREAS
 uint8_t *AreaInfo::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
   uint8_t *__restrict__ pos = buffer.get_pos();
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 1, this->area_id);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 2, this->name);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 18, this->name);
   return pos;
 }
 uint32_t AreaInfo::calculate_size() const {
   uint32_t size = 0;
   size += ProtoSize::calc_uint32(1, this->area_id);
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   return size;
 }
 #endif
@@ -65,14 +65,14 @@ uint32_t AreaInfo::calculate_size() const {
 uint8_t *DeviceInfo::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
   uint8_t *__restrict__ pos = buffer.get_pos();
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 1, this->device_id);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 2, this->name);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 18, this->name);
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 3, this->area_id);
   return pos;
 }
 uint32_t DeviceInfo::calculate_size() const {
   uint32_t size = 0;
   size += ProtoSize::calc_uint32(1, this->device_id);
-  size += ProtoSize::calc_length(1, this->name.size());
+  size += 2 + this->name.size();
   size += ProtoSize::calc_uint32(1, this->area_id);
   return size;
 }
@@ -93,10 +93,10 @@ uint32_t SerialProxyInfo::calculate_size() const {
 #endif
 uint8_t *DeviceInfoResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
   uint8_t *__restrict__ pos = buffer.get_pos();
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 2, this->name);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 3, this->mac_address);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 4, this->esphome_version);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 5, this->compilation_time);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 18, this->name);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 26, this->mac_address);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 34, this->esphome_version);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 42, this->compilation_time);
   ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 6, this->model);
 #ifdef USE_DEEP_SLEEP
   ProtoEncode::encode_bool(pos PROTO_ENCODE_DEBUG_ARG, 7, this->has_deep_sleep);
@@ -113,8 +113,8 @@ uint8_t *DeviceInfoResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_
 #ifdef USE_BLUETOOTH_PROXY
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 15, this->bluetooth_proxy_feature_flags);
 #endif
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 12, this->manufacturer);
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 13, this->friendly_name);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 98, this->manufacturer);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 106, this->friendly_name);
 #ifdef USE_VOICE_ASSISTANT
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 17, this->voice_assistant_feature_flags);
 #endif
@@ -122,7 +122,7 @@ uint8_t *DeviceInfoResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_
   ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 16, this->suggested_area);
 #endif
 #ifdef USE_BLUETOOTH_PROXY
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 18, this->bluetooth_mac_address);
+  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 18, this->bluetooth_mac_address, true);
 #endif
 #ifdef USE_API_NOISE
   ProtoEncode::encode_bool(pos PROTO_ENCODE_DEBUG_ARG, 19, this->api_encryption_supported);
@@ -155,10 +155,10 @@ uint8_t *DeviceInfoResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_
 }
 uint32_t DeviceInfoResponse::calculate_size() const {
   uint32_t size = 0;
-  size += ProtoSize::calc_length(1, this->name.size());
-  size += ProtoSize::calc_length(1, this->mac_address.size());
-  size += ProtoSize::calc_length(1, this->esphome_version.size());
-  size += ProtoSize::calc_length(1, this->compilation_time.size());
+  size += 2 + this->name.size();
+  size += 2 + this->mac_address.size();
+  size += 2 + this->esphome_version.size();
+  size += 2 + this->compilation_time.size();
   size += ProtoSize::calc_length(1, this->model.size());
 #ifdef USE_DEEP_SLEEP
   size += ProtoSize::calc_bool(1, this->has_deep_sleep);
@@ -175,8 +175,8 @@ uint32_t DeviceInfoResponse::calculate_size() const {
 #ifdef USE_BLUETOOTH_PROXY
   size += ProtoSize::calc_uint32(1, this->bluetooth_proxy_feature_flags);
 #endif
-  size += ProtoSize::calc_length(1, this->manufacturer.size());
-  size += ProtoSize::calc_length(1, this->friendly_name.size());
+  size += 2 + this->manufacturer.size();
+  size += 2 + this->friendly_name.size();
 #ifdef USE_VOICE_ASSISTANT
   size += ProtoSize::calc_uint32(2, this->voice_assistant_feature_flags);
 #endif
@@ -184,7 +184,7 @@ uint32_t DeviceInfoResponse::calculate_size() const {
   size += ProtoSize::calc_length(2, this->suggested_area.size());
 #endif
 #ifdef USE_BLUETOOTH_PROXY
-  size += ProtoSize::calc_length(2, this->bluetooth_mac_address.size());
+  size += 3 + this->bluetooth_mac_address.size();
 #endif
 #ifdef USE_API_NOISE
   size += ProtoSize::calc_bool(2, this->api_encryption_supported);