diff --git a/esphome/components/api/api.proto b/esphome/components/api/api.proto
index 8e3b5a1ffb1..0a49a76c115 100644
--- a/esphome/components/api/api.proto
+++ b/esphome/components/api/api.proto
@@ -225,6 +225,8 @@ message SerialProxyInfo {
 //   esphome_version = 32 (ESPHOME_VERSION string literal)
 //   compilation_time = 25 (Application::BUILD_TIME_STR_SIZE - 1, constexpr)
 //   manufacturer = 20 (longest hardcoded literal: "Nordic Semiconductor")
+//   model = 127 (core/config.BOARD_MAX_LENGTH, validated in platform schemas)
+//   project_name/project_version = 127 (core/config.PROJECT_MAX_LENGTH)
 message DeviceInfoResponse {
   option (id) = 10;
   option (source) = SOURCE_SERVER;
@@ -248,13 +250,15 @@ message DeviceInfoResponse {
   string compilation_time = 5 [(max_data_length) = 25, (force) = true];
 
   // The model of the board. For example NodeMCU
-  string model = 6;
+  // max_data_length matches core/config.BOARD_MAX_LENGTH (validated in platform schemas)
+  string model = 6 [(max_data_length) = 127, (force) = true];
 
   bool has_deep_sleep = 7 [(field_ifdef) = "USE_DEEP_SLEEP"];
 
   // The esphome project details if set
-  string project_name = 8 [(field_ifdef) = "ESPHOME_PROJECT_NAME"];
-  string project_version = 9 [(field_ifdef) = "ESPHOME_PROJECT_NAME"];
+  // max_data_length matches core/config.PROJECT_MAX_LENGTH
+  string project_name = 8 [(max_data_length) = 127, (force) = true, (field_ifdef) = "ESPHOME_PROJECT_NAME"];
+  string project_version = 9 [(max_data_length) = 127, (force) = true, (field_ifdef) = "ESPHOME_PROJECT_NAME"];
 
   uint32 webserver_port = 10 [(field_ifdef) = "USE_WEBSERVER"];
 
diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index 66996452fab..64adc8bc9e7 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -97,15 +97,15 @@ uint8_t *DeviceInfoResponse::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_
   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);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 50, this->model);
 #ifdef USE_DEEP_SLEEP
   ProtoEncode::encode_bool(pos PROTO_ENCODE_DEBUG_ARG, 7, this->has_deep_sleep);
 #endif
 #ifdef ESPHOME_PROJECT_NAME
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 8, this->project_name);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 66, this->project_name);
 #endif
 #ifdef ESPHOME_PROJECT_NAME
-  ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 9, this->project_version);
+  ProtoEncode::encode_short_string_force(pos PROTO_ENCODE_DEBUG_ARG, 74, this->project_version);
 #endif
 #ifdef USE_WEBSERVER
   ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 10, this->webserver_port);
@@ -159,15 +159,15 @@ uint32_t DeviceInfoResponse::calculate_size() const {
   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());
+  size += 2 + this->model.size();
 #ifdef USE_DEEP_SLEEP
   size += ProtoSize::calc_bool(1, this->has_deep_sleep);
 #endif
 #ifdef ESPHOME_PROJECT_NAME
-  size += ProtoSize::calc_length(1, this->project_name.size());
+  size += 2 + this->project_name.size();
 #endif
 #ifdef ESPHOME_PROJECT_NAME
-  size += ProtoSize::calc_length(1, this->project_version.size());
+  size += 2 + this->project_version.size();
 #endif
 #ifdef USE_WEBSERVER
   size += ProtoSize::calc_uint32(1, this->webserver_port);
diff --git a/esphome/components/esp32/__init__.py b/esphome/components/esp32/__init__.py
index 0d8a2215245..54eecb5ad1f 100644
--- a/esphome/components/esp32/__init__.py
+++ b/esphome/components/esp32/__init__.py
@@ -44,6 +44,7 @@ from esphome.const import (
     __version__,
 )
 from esphome.core import CORE, HexInt
+from esphome.core.config import BOARD_MAX_LENGTH
 from esphome.coroutine import CoroPriority, coroutine_with_priority
 import esphome.final_validate as fv
 from esphome.helpers import copy_file_if_changed, rmtree, write_file_if_changed
@@ -1403,7 +1404,9 @@ CONF_PARTITIONS = "partitions"
 CONFIG_SCHEMA = cv.All(
     cv.Schema(
         {
-            cv.Optional(CONF_BOARD): cv.string_strict,
+            cv.Optional(CONF_BOARD): cv.All(
+                cv.string_strict, cv.Length(max=BOARD_MAX_LENGTH)
+            ),
             cv.Optional(CONF_CPU_FREQUENCY): cv.one_of(
                 *FULL_CPU_FREQUENCIES, upper=True
             ),
diff --git a/esphome/components/esp8266/__init__.py b/esphome/components/esp8266/__init__.py
index fcd3499b151..76c8b1e870a 100644
--- a/esphome/components/esp8266/__init__.py
+++ b/esphome/components/esp8266/__init__.py
@@ -20,6 +20,7 @@ from esphome.const import (
     ThreadModel,
 )
 from esphome.core import CORE, CoroPriority, Lambda, coroutine_with_priority
+from esphome.core.config import BOARD_MAX_LENGTH
 from esphome.helpers import copy_file_if_changed
 from esphome.types import ConfigType
 
@@ -203,7 +204,9 @@ BUILD_FLASH_MODES = ["qio", "qout", "dio", "dout"]
 CONFIG_SCHEMA = cv.All(
     cv.Schema(
         {
-            cv.Required(CONF_BOARD): cv.string_strict,
+            cv.Required(CONF_BOARD): cv.All(
+                cv.string_strict, cv.Length(max=BOARD_MAX_LENGTH)
+            ),
             cv.Optional(CONF_FRAMEWORK, default={}): ARDUINO_FRAMEWORK_SCHEMA,
             cv.Optional(CONF_RESTORE_FROM_FLASH, default=False): cv.boolean,
             cv.Optional(CONF_EARLY_PIN_INIT, default=True): cv.boolean,
diff --git a/esphome/components/libretiny/__init__.py b/esphome/components/libretiny/__init__.py
index 8f991246040..00be620831b 100644
--- a/esphome/components/libretiny/__init__.py
+++ b/esphome/components/libretiny/__init__.py
@@ -23,6 +23,7 @@ from esphome.const import (
     __version__,
 )
 from esphome.core import CORE
+from esphome.core.config import BOARD_MAX_LENGTH
 from esphome.storage_json import StorageJSON
 
 from . import gpio  # noqa
@@ -266,7 +267,9 @@ CONFIG_SCHEMA = cv.All(_notify_old_style)
 BASE_SCHEMA = cv.Schema(
     {
         cv.GenerateID(): cv.declare_id(LTComponent),
-        cv.Required(CONF_BOARD): cv.string_strict,
+        cv.Required(CONF_BOARD): cv.All(
+            cv.string_strict, cv.Length(max=BOARD_MAX_LENGTH)
+        ),
         cv.Optional(CONF_FAMILY): cv.one_of(*FAMILIES, upper=True),
         cv.Optional(CONF_FRAMEWORK, default={}): FRAMEWORK_SCHEMA,
     },
diff --git a/esphome/components/nrf52/__init__.py b/esphome/components/nrf52/__init__.py
index 5054e5e0df4..566aefb2090 100644
--- a/esphome/components/nrf52/__init__.py
+++ b/esphome/components/nrf52/__init__.py
@@ -46,6 +46,7 @@ from esphome.const import (
     ThreadModel,
 )
 from esphome.core import CORE, CoroPriority, EsphomeError, coroutine_with_priority
+from esphome.core.config import BOARD_MAX_LENGTH
 import esphome.final_validate as fv
 from esphome.storage_json import StorageJSON
 from esphome.types import ConfigType
@@ -145,7 +146,9 @@ CONFIG_SCHEMA = cv.All(
     set_core_data,
     cv.Schema(
         {
-            cv.Required(CONF_BOARD): cv.string_strict,
+            cv.Required(CONF_BOARD): cv.All(
+                cv.string_strict, cv.Length(max=BOARD_MAX_LENGTH)
+            ),
             cv.Optional(KEY_BOOTLOADER): cv.one_of(*BOOTLOADERS, lower=True),
             cv.Optional(CONF_DFU): cv.Schema(
                 {
diff --git a/esphome/components/rp2040/__init__.py b/esphome/components/rp2040/__init__.py
index 0bb18110693..628cdf370a0 100644
--- a/esphome/components/rp2040/__init__.py
+++ b/esphome/components/rp2040/__init__.py
@@ -22,6 +22,7 @@ from esphome.const import (
     ThreadModel,
 )
 from esphome.core import CORE, CoroPriority, EsphomeError, coroutine_with_priority
+from esphome.core.config import BOARD_MAX_LENGTH
 from esphome.helpers import copy_file_if_changed, read_file, write_file_if_changed
 
 from . import boards
@@ -168,7 +169,9 @@ ARDUINO_FRAMEWORK_SCHEMA = cv.All(
 CONFIG_SCHEMA = cv.All(
     cv.Schema(
         {
-            cv.Required(CONF_BOARD): cv.string_strict,
+            cv.Required(CONF_BOARD): cv.All(
+                cv.string_strict, cv.Length(max=BOARD_MAX_LENGTH)
+            ),
             cv.Optional(CONF_FRAMEWORK, default={}): ARDUINO_FRAMEWORK_SCHEMA,
             cv.Optional(CONF_WATCHDOG_TIMEOUT, default="8388ms"): cv.All(
                 cv.positive_time_period_milliseconds,
diff --git a/esphome/core/config.py b/esphome/core/config.py
index 31cfd00ef7a..efc6d62f481 100644
--- a/esphome/core/config.py
+++ b/esphome/core/config.py
@@ -236,6 +236,12 @@ ICON_MAX_LENGTH = 63
 # Max unit of measurement string length
 UNIT_OF_MEASUREMENT_MAX_LENGTH = 63
 
+# Max project name/version string length (must fit in single-byte varint for proto encoding)
+PROJECT_MAX_LENGTH = 127
+
+# Max board/model string length (must fit in single-byte varint for proto encoding)
+BOARD_MAX_LENGTH = 127
+
 AREA_SCHEMA = cv.Schema(
     {
         cv.GenerateID(CONF_ID): cv.declare_id(Area),
@@ -306,9 +312,13 @@ CONFIG_SCHEMA = cv.All(
             cv.Optional(CONF_PROJECT): cv.Schema(
                 {
                     cv.Required(CONF_NAME): cv.All(
-                        cv.string_strict, valid_project_name
+                        cv.string_strict,
+                        valid_project_name,
+                        cv.Length(max=PROJECT_MAX_LENGTH),
+                    ),
+                    cv.Required(CONF_VERSION): cv.All(
+                        cv.string_strict, cv.Length(max=PROJECT_MAX_LENGTH)
                     ),
-                    cv.Required(CONF_VERSION): cv.string_strict,
                     cv.Optional(CONF_ON_UPDATE): automation.validate_automation(
                         {
                             cv.GenerateID(CONF_TRIGGER_ID): cv.declare_id(