From 0193464f92e90f765242b6ce0837f009ee611cdb Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:34:49 -1000
Subject: [PATCH 01/12] [dsmr] Avoid std::string allocation for decryption key
 (#13375)

---
 esphome/components/dsmr/__init__.py | 22 +++-------------------
 esphome/components/dsmr/dsmr.cpp    | 19 +++++++------------
 esphome/components/dsmr/dsmr.h      |  2 +-
 esphome/config_validation.py        |  8 ++++----
 4 files changed, 15 insertions(+), 36 deletions(-)

diff --git a/esphome/components/dsmr/__init__.py b/esphome/components/dsmr/__init__.py
index 0ba68daf5d..386da3ce21 100644
--- a/esphome/components/dsmr/__init__.py
+++ b/esphome/components/dsmr/__init__.py
@@ -25,29 +25,13 @@ dsmr_ns = cg.esphome_ns.namespace("esphome::dsmr")
 Dsmr = dsmr_ns.class_("Dsmr", cg.Component, uart.UARTDevice)
 
 
-def _validate_key(value):
-    value = cv.string_strict(value)
-    parts = [value[i : i + 2] for i in range(0, len(value), 2)]
-    if len(parts) != 16:
-        raise cv.Invalid("Decryption key must consist of 16 hexadecimal numbers")
-    parts_int = []
-    if any(len(part) != 2 for part in parts):
-        raise cv.Invalid("Decryption key must be format XX")
-    for part in parts:
-        try:
-            parts_int.append(int(part, 16))
-        except ValueError:
-            # pylint: disable=raise-missing-from
-            raise cv.Invalid("Decryption key must be hex values from 00 to FF")
-
-    return "".join(f"{part:02X}" for part in parts_int)
-
-
 CONFIG_SCHEMA = cv.All(
     cv.Schema(
         {
             cv.GenerateID(): cv.declare_id(Dsmr),
-            cv.Optional(CONF_DECRYPTION_KEY): _validate_key,
+            cv.Optional(CONF_DECRYPTION_KEY): lambda value: cv.bind_key(
+                value, name="Decryption key"
+            ),
             cv.Optional(CONF_CRC_CHECK, default=True): cv.boolean,
             cv.Optional(CONF_GAS_MBUS_ID, default=1): cv.int_,
             cv.Optional(CONF_WATER_MBUS_ID, default=2): cv.int_,
diff --git a/esphome/components/dsmr/dsmr.cpp b/esphome/components/dsmr/dsmr.cpp
index 5c62aa93ab..c78d37bf5e 100644
--- a/esphome/components/dsmr/dsmr.cpp
+++ b/esphome/components/dsmr/dsmr.cpp
@@ -1,4 +1,5 @@
 #include "dsmr.h"
+#include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 
 #include <AES.h>
@@ -294,8 +295,8 @@ void Dsmr::dump_config() {
   DSMR_TEXT_SENSOR_LIST(DSMR_LOG_TEXT_SENSOR, )
 }
 
-void Dsmr::set_decryption_key(const std::string &decryption_key) {
-  if (decryption_key.empty()) {
+void Dsmr::set_decryption_key(const char *decryption_key) {
+  if (decryption_key == nullptr || decryption_key[0] == '\0') {
     ESP_LOGI(TAG, "Disabling decryption");
     this->decryption_key_.clear();
     if (this->crypt_telegram_ != nullptr) {
@@ -305,21 +306,15 @@ void Dsmr::set_decryption_key(const std::string &decryption_key) {
     return;
   }
 
-  if (decryption_key.length() != 32) {
-    ESP_LOGE(TAG, "Error, decryption key must be 32 character long");
+  if (!parse_hex(decryption_key, this->decryption_key_, 16)) {
+    ESP_LOGE(TAG, "Error, decryption key must be 32 hex characters");
+    this->decryption_key_.clear();
     return;
   }
-  this->decryption_key_.clear();
 
   ESP_LOGI(TAG, "Decryption key is set");
   // Verbose level prints decryption key
-  ESP_LOGV(TAG, "Using decryption key: %s", decryption_key.c_str());
-
-  char temp[3] = {0};
-  for (int i = 0; i < 16; i++) {
-    strncpy(temp, &(decryption_key.c_str()[i * 2]), 2);
-    this->decryption_key_.push_back(std::strtoul(temp, nullptr, 16));
-  }
+  ESP_LOGV(TAG, "Using decryption key: %s", decryption_key);
 
   if (this->crypt_telegram_ == nullptr) {
     this->crypt_telegram_ = new uint8_t[this->max_telegram_len_];  // NOLINT
diff --git a/esphome/components/dsmr/dsmr.h b/esphome/components/dsmr/dsmr.h
index 56ba75b5fa..b7e05a22b3 100644
--- a/esphome/components/dsmr/dsmr.h
+++ b/esphome/components/dsmr/dsmr.h
@@ -63,7 +63,7 @@ class Dsmr : public Component, public uart::UARTDevice {
 
   void dump_config() override;
 
-  void set_decryption_key(const std::string &decryption_key);
+  void set_decryption_key(const char *decryption_key);
   void set_max_telegram_length(size_t length) { this->max_telegram_len_ = length; }
   void set_request_pin(GPIOPin *request_pin) { this->request_pin_ = request_pin; }
   void set_request_interval(uint32_t interval) { this->request_interval_ = interval; }
diff --git a/esphome/config_validation.py b/esphome/config_validation.py
index 8e2fadbea8..b7ab02013d 100644
--- a/esphome/config_validation.py
+++ b/esphome/config_validation.py
@@ -1046,20 +1046,20 @@ def mac_address(value):
     return core.MACAddress(*parts_int)
 
 
-def bind_key(value):
+def bind_key(value, *, name="Bind key"):
     value = string_strict(value)
     parts = [value[i : i + 2] for i in range(0, len(value), 2)]
     if len(parts) != 16:
-        raise Invalid("Bind key must consist of 16 hexadecimal numbers")
+        raise Invalid(f"{name} must consist of 16 hexadecimal numbers")
     parts_int = []
     if any(len(part) != 2 for part in parts):
-        raise Invalid("Bind key must be format XX")
+        raise Invalid(f"{name} must be format XX")
     for part in parts:
         try:
             parts_int.append(int(part, 16))
         except ValueError:
             # pylint: disable=raise-missing-from
-            raise Invalid("Bind key must be hex values from 00 to FF")
+            raise Invalid(f"{name} must be hex values from 00 to FF")
 
     return "".join(f"{part:02X}" for part in parts_int)
 

From 8ec31dd7693028d1e987d39b67708c04133ebc66 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:35:19 -1000
Subject: [PATCH 02/12] [voice_assistant] Deprecate Timer::to_string() in favor
 of heap-free to_str() (#13377)

---
 esphome/components/voice_assistant/voice_assistant.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/esphome/components/voice_assistant/voice_assistant.h b/esphome/components/voice_assistant/voice_assistant.h
index b1b3df7bbd..d61a8fbbc1 100644
--- a/esphome/components/voice_assistant/voice_assistant.h
+++ b/esphome/components/voice_assistant/voice_assistant.h
@@ -81,6 +81,8 @@ struct Timer {
              this->id.c_str(), this->name.c_str(), this->total_seconds, this->seconds_left, YESNO(this->is_active));
     return buffer.data();
   }
+  // Remove before 2026.8.0
+  ESPDEPRECATED("Use to_str() instead. Removed in 2026.8.0", "2026.2.0")
   std::string to_string() const {
     char buffer[TO_STR_BUFFER_SIZE];
     return this->to_str(buffer);

From 8998ef0bc309ec1ed5f97dc8ab372a6c5007f332 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:35:32 -1000
Subject: [PATCH 03/12] [network] Deprecate IPAddress::str() in favor of
 heap-free str_to() (#13378)

---
 esphome/components/network/ip_address.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/esphome/components/network/ip_address.h b/esphome/components/network/ip_address.h
index 3dfcf0cb64..d0ac8164af 100644
--- a/esphome/components/network/ip_address.h
+++ b/esphome/components/network/ip_address.h
@@ -60,6 +60,8 @@ struct IPAddress {
   }
   IPAddress(const std::string &in_address) { inet_aton(in_address.c_str(), &ip_addr_); }
   IPAddress(const ip_addr_t *other_ip) { ip_addr_ = *other_ip; }
+  // Remove before 2026.8.0
+  ESPDEPRECATED("Use str_to() instead. Removed in 2026.8.0", "2026.2.0")
   std::string str() const {
     char buf[IP_ADDRESS_BUFFER_SIZE];
     this->str_to(buf);
@@ -147,6 +149,8 @@ struct IPAddress {
   bool is_ip4() const { return IP_IS_V4(&ip_addr_); }
   bool is_ip6() const { return IP_IS_V6(&ip_addr_); }
   bool is_multicast() const { return ip_addr_ismulticast(&ip_addr_); }
+  // Remove before 2026.8.0
+  ESPDEPRECATED("Use str_to() instead. Removed in 2026.8.0", "2026.2.0")
   std::string str() const {
     char buf[IP_ADDRESS_BUFFER_SIZE];
     this->str_to(buf);

From 5d787e2512aecfb7ef434a00e3cca74d51c67f4d Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:35:58 -1000
Subject: [PATCH 04/12] [sprinkler] Eliminate std::string heap allocations
 (#13379)

---
 esphome/components/sprinkler/sprinkler.cpp | 20 +++++++++-----------
 esphome/components/sprinkler/sprinkler.h   |  8 ++++----
 2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/esphome/components/sprinkler/sprinkler.cpp b/esphome/components/sprinkler/sprinkler.cpp
index 2813b4450b..35310fa2f9 100644
--- a/esphome/components/sprinkler/sprinkler.cpp
+++ b/esphome/components/sprinkler/sprinkler.cpp
@@ -327,14 +327,13 @@ SprinklerValveOperator *SprinklerValveRunRequest::valve_operator() { return this
 
 SprinklerValveRunRequestOrigin SprinklerValveRunRequest::request_is_from() { return this->origin_; }
 
-Sprinkler::Sprinkler() {}
-Sprinkler::Sprinkler(const std::string &name) {
-  // The `name` is needed to set timers up, hence non-default constructor
-  // replaces `set_name()` method previously existed
-  this->name_ = name;
+Sprinkler::Sprinkler() : Sprinkler("") {}
+Sprinkler::Sprinkler(const char *name) : name_(name) {
+  // The `name` is stored for dump_config logging
   this->timer_.init(2);
-  this->timer_.push_back({this->name_ + "sm", false, 0, 0, std::bind(&Sprinkler::sm_timer_callback_, this)});
-  this->timer_.push_back({this->name_ + "vs", false, 0, 0, std::bind(&Sprinkler::valve_selection_callback_, this)});
+  // Timer names only need to be unique within this component instance
+  this->timer_.push_back({"sm", false, 0, 0, std::bind(&Sprinkler::sm_timer_callback_, this)});
+  this->timer_.push_back({"vs", false, 0, 0, std::bind(&Sprinkler::valve_selection_callback_, this)});
 }
 
 void Sprinkler::setup() { this->all_valves_off_(true); }
@@ -1575,8 +1574,7 @@ const LogString *Sprinkler::state_as_str_(SprinklerState state) {
 
 void Sprinkler::start_timer_(const SprinklerTimerIndex timer_index) {
   if (this->timer_duration_(timer_index) > 0) {
-    // FixedVector ensures timer_ can't be resized, so .c_str() pointers remain valid
-    this->set_timeout(this->timer_[timer_index].name.c_str(), this->timer_duration_(timer_index),
+    this->set_timeout(this->timer_[timer_index].name, this->timer_duration_(timer_index),
                       this->timer_cbf_(timer_index));
     this->timer_[timer_index].start_time = millis();
     this->timer_[timer_index].active = true;
@@ -1587,7 +1585,7 @@ void Sprinkler::start_timer_(const SprinklerTimerIndex timer_index) {
 
 bool Sprinkler::cancel_timer_(const SprinklerTimerIndex timer_index) {
   this->timer_[timer_index].active = false;
-  return this->cancel_timeout(this->timer_[timer_index].name.c_str());
+  return this->cancel_timeout(this->timer_[timer_index].name);
 }
 
 bool Sprinkler::timer_active_(const SprinklerTimerIndex timer_index) { return this->timer_[timer_index].active; }
@@ -1618,7 +1616,7 @@ void Sprinkler::sm_timer_callback_() {
 }
 
 void Sprinkler::dump_config() {
-  ESP_LOGCONFIG(TAG, "Sprinkler Controller -- %s", this->name_.c_str());
+  ESP_LOGCONFIG(TAG, "Sprinkler Controller -- %s", this->name_);
   if (this->manual_selection_delay_.has_value()) {
     ESP_LOGCONFIG(TAG, "  Manual Selection Delay: %" PRIu32 " seconds", this->manual_selection_delay_.value_or(0));
   }
diff --git a/esphome/components/sprinkler/sprinkler.h b/esphome/components/sprinkler/sprinkler.h
index 273c0e9208..04efa28031 100644
--- a/esphome/components/sprinkler/sprinkler.h
+++ b/esphome/components/sprinkler/sprinkler.h
@@ -11,7 +11,7 @@
 
 namespace esphome::sprinkler {
 
-const std::string MIN_STR = "min";
+inline constexpr const char *MIN_STR = "min";
 
 enum SprinklerState : uint8_t {
   // NOTE: these states are used by both SprinklerValveOperator and Sprinkler (the controller)!
@@ -49,7 +49,7 @@ struct SprinklerQueueItem {
 };
 
 struct SprinklerTimer {
-  const std::string name;
+  const char *name;
   bool active;
   uint32_t time;
   uint32_t start_time;
@@ -176,7 +176,7 @@ class SprinklerValveRunRequest {
 class Sprinkler : public Component {
  public:
   Sprinkler();
-  Sprinkler(const std::string &name);
+  Sprinkler(const char *name);
   void setup() override;
   void loop() override;
   void dump_config() override;
@@ -504,7 +504,7 @@ class Sprinkler : public Component {
   uint32_t start_delay_{0};
   uint32_t stop_delay_{0};
 
-  std::string name_;
+  const char *name_{""};
 
   /// Sprinkler controller state
   SprinklerState state_{IDLE};

From b5fe271d6bc9cc069d31e2c8706594c2b819eb09 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:36:47 -1000
Subject: [PATCH 05/12] [sprinkler] Disable loops when idle to reduce CPU
 overhead (#13381)

---
 esphome/components/sprinkler/sprinkler.cpp | 36 +++++++++++++++-------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/esphome/components/sprinkler/sprinkler.cpp b/esphome/components/sprinkler/sprinkler.cpp
index 35310fa2f9..369ee5e6ff 100644
--- a/esphome/components/sprinkler/sprinkler.cpp
+++ b/esphome/components/sprinkler/sprinkler.cpp
@@ -43,13 +43,11 @@ SprinklerControllerSwitch::SprinklerControllerSwitch()
     : turn_on_trigger_(new Trigger<>()), turn_off_trigger_(new Trigger<>()) {}
 
 void SprinklerControllerSwitch::loop() {
-  if (!this->f_.has_value())
-    return;
+  // Loop is only enabled when f_ has a value (see setup())
   auto s = (*this->f_)();
-  if (!s.has_value())
-    return;
-
-  this->publish_state(*s);
+  if (s.has_value()) {
+    this->publish_state(*s);
+  }
 }
 
 void SprinklerControllerSwitch::write_state(bool state) {
@@ -74,7 +72,13 @@ float SprinklerControllerSwitch::get_setup_priority() const { return setup_prior
 Trigger<> *SprinklerControllerSwitch::get_turn_on_trigger() const { return this->turn_on_trigger_; }
 Trigger<> *SprinklerControllerSwitch::get_turn_off_trigger() const { return this->turn_off_trigger_; }
 
-void SprinklerControllerSwitch::setup() { this->state = this->get_initial_state_with_restore_mode().value_or(false); }
+void SprinklerControllerSwitch::setup() {
+  this->state = this->get_initial_state_with_restore_mode().value_or(false);
+  // Disable loop if no state lambda is set - nothing to poll
+  if (!this->f_.has_value()) {
+    this->disable_loop();
+  }
+}
 
 void SprinklerControllerSwitch::dump_config() { LOG_SWITCH("", "Sprinkler Switch", this); }
 
@@ -336,15 +340,23 @@ Sprinkler::Sprinkler(const char *name) : name_(name) {
   this->timer_.push_back({"vs", false, 0, 0, std::bind(&Sprinkler::valve_selection_callback_, this)});
 }
 
-void Sprinkler::setup() { this->all_valves_off_(true); }
+void Sprinkler::setup() {
+  this->all_valves_off_(true);
+  // Start with loop disabled - nothing to do when idle
+  this->disable_loop();
+}
 
 void Sprinkler::loop() {
   for (auto &vo : this->valve_op_) {
     vo.loop();
   }
-  if (this->prev_req_.has_request() && this->prev_req_.has_valve_operator() &&
-      this->prev_req_.valve_operator()->state() == IDLE) {
-    this->prev_req_.reset();
+  if (this->prev_req_.has_request()) {
+    if (this->prev_req_.has_valve_operator() && this->prev_req_.valve_operator()->state() == IDLE) {
+      this->prev_req_.reset();
+    }
+  } else if (this->state_ == IDLE) {
+    // Nothing more to do - disable loop until next activation
+    this->disable_loop();
   }
 }
 
@@ -1332,6 +1344,8 @@ void Sprinkler::start_valve_(SprinklerValveRunRequest *req) {
   if (!this->is_a_valid_valve(req->valve())) {
     return;  // we can't do anything if the valve number isn't valid
   }
+  // Enable loop to monitor valve operator states
+  this->enable_loop();
   for (auto &vo : this->valve_op_) {  // find the first available SprinklerValveOperator, load it and start it up
     if (vo.state() == IDLE) {
       auto run_duration = req->run_duration() ? req->run_duration() : this->valve_run_duration_adjusted(req->valve());

From 62b6c9bf7cee3a67fab39f6dc9870d69add352dd Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:37:03 -1000
Subject: [PATCH 06/12] [esp32_ble] Deprecate ESPBTUUID::to_string() in favor
 of heap-free to_str() (#13376)

---
 esphome/components/esp32_ble/ble_uuid.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/esphome/components/esp32_ble/ble_uuid.h b/esphome/components/esp32_ble/ble_uuid.h
index ae593955a4..6c8ef7bfd9 100644
--- a/esphome/components/esp32_ble/ble_uuid.h
+++ b/esphome/components/esp32_ble/ble_uuid.h
@@ -46,6 +46,8 @@ class ESPBTUUID {
 
   esp_bt_uuid_t get_uuid() const;
 
+  // Remove before 2026.8.0
+  ESPDEPRECATED("Use to_str() instead. Removed in 2026.8.0", "2026.2.0")
   std::string to_string() const;
   const char *to_str(std::span<char, UUID_STR_LEN> output) const;
 

From 4e0e7796ded16e118bb95ff63fc956850d9b3e7f Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:37:19 -1000
Subject: [PATCH 07/12] [mqtt] Remove unnecessary defer in ESP8266 on_message
 callback (#13373)

---
 esphome/components/mqtt/mqtt_client.cpp | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/esphome/components/mqtt/mqtt_client.cpp b/esphome/components/mqtt/mqtt_client.cpp
index 7d4050284f..f8517c4f89 100644
--- a/esphome/components/mqtt/mqtt_client.cpp
+++ b/esphome/components/mqtt/mqtt_client.cpp
@@ -610,18 +610,10 @@ static bool topic_match(const char *message, const char *subscription) {
 }
 
 void MQTTClientComponent::on_message(const std::string &topic, const std::string &payload) {
-#ifdef USE_ESP8266
-  // on ESP8266, this is called in lwIP/AsyncTCP task; some components do not like running
-  // from a different task.
-  this->defer([this, topic, payload]() {
-#endif
-    for (auto &subscription : this->subscriptions_) {
-      if (topic_match(topic.c_str(), subscription.topic.c_str()))
-        subscription.callback(topic, payload);
-    }
-#ifdef USE_ESP8266
-  });
-#endif
+  for (auto &subscription : this->subscriptions_) {
+    if (topic_match(topic.c_str(), subscription.topic.c_str()))
+      subscription.callback(topic, payload);
+  }
 }
 
 // Setters

From 8ade9dfc107b752bb5ac3cf03936f75bb85f5af6 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:37:33 -1000
Subject: [PATCH 08/12] [shtcx] Use LogString for type to_string to save RAM on
 ESP8266 (#13370)

---
 esphome/components/shtcx/shtcx.cpp | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/esphome/components/shtcx/shtcx.cpp b/esphome/components/shtcx/shtcx.cpp
index 933dd9bde9..aca305b88d 100644
--- a/esphome/components/shtcx/shtcx.cpp
+++ b/esphome/components/shtcx/shtcx.cpp
@@ -13,14 +13,14 @@ static const uint16_t SHTCX_COMMAND_READ_ID_REGISTER = 0xEFC8;
 static const uint16_t SHTCX_COMMAND_SOFT_RESET = 0x805D;
 static const uint16_t SHTCX_COMMAND_POLLING_H = 0x7866;
 
-inline const char *to_string(SHTCXType type) {
+static const LogString *shtcx_type_to_string(SHTCXType type) {
   switch (type) {
     case SHTCX_TYPE_SHTC3:
-      return "SHTC3";
+      return LOG_STR("SHTC3");
     case SHTCX_TYPE_SHTC1:
-      return "SHTC1";
+      return LOG_STR("SHTC1");
     default:
-      return "UNKNOWN";
+      return LOG_STR("UNKNOWN");
   }
 }
 
@@ -52,7 +52,7 @@ void SHTCXComponent::dump_config() {
   ESP_LOGCONFIG(TAG,
                 "SHTCx:\n"
                 "  Model: %s (%04x)",
-                to_string(this->type_), this->sensor_id_);
+                LOG_STR_ARG(shtcx_type_to_string(this->type_)), this->sensor_id_);
   LOG_I2C_DEVICE(this);
   if (this->is_failed()) {
     ESP_LOGE(TAG, ESP_LOG_MSG_COMM_FAIL);

From b48d4ab785f1deb84d59865b2a0abb9adc69a44f Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:37:54 -1000
Subject: [PATCH 09/12] [mqtt] Reduce heap allocations in publish path (#13372)

---
 esphome/components/mqtt/mqtt_client.cpp | 51 ++++++++++++++++---------
 esphome/components/mqtt/mqtt_client.h   |  6 +++
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/esphome/components/mqtt/mqtt_client.cpp b/esphome/components/mqtt/mqtt_client.cpp
index f8517c4f89..96eba37a57 100644
--- a/esphome/components/mqtt/mqtt_client.cpp
+++ b/esphome/components/mqtt/mqtt_client.cpp
@@ -5,6 +5,7 @@
 #include <utility>
 #include "esphome/components/network/util.h"
 #include "esphome/core/application.h"
+#include "esphome/core/entity_base.h"
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include "esphome/core/version.h"
@@ -66,10 +67,13 @@ void MQTTClientComponent::setup() {
         "esphome/discover", [this](const std::string &topic, const std::string &payload) { this->send_device_info_(); },
         2);
 
-    std::string topic = "esphome/ping/";
-    topic.append(App.get_name());
+    // Format topic on stack - subscribe() copies it
+    // "esphome/ping/" (13) + name (ESPHOME_DEVICE_NAME_MAX_LEN) + null (1)
+    constexpr size_t ping_topic_buffer_size = 13 + ESPHOME_DEVICE_NAME_MAX_LEN + 1;
+    char ping_topic[ping_topic_buffer_size];
+    buf_append_printf(ping_topic, sizeof(ping_topic), 0, "esphome/ping/%s", App.get_name().c_str());
     this->subscribe(
-        topic, [this](const std::string &topic, const std::string &payload) { this->send_device_info_(); }, 2);
+        ping_topic, [this](const std::string &topic, const std::string &payload) { this->send_device_info_(); }, 2);
   }
 
   if (this->enable_on_boot_) {
@@ -81,8 +85,11 @@ void MQTTClientComponent::send_device_info_() {
   if (!this->is_connected() or !this->is_discovery_ip_enabled()) {
     return;
   }
-  std::string topic = "esphome/discover/";
-  topic.append(App.get_name());
+  // Format topic on stack to avoid heap allocation
+  // "esphome/discover/" (17) + name (ESPHOME_DEVICE_NAME_MAX_LEN) + null (1)
+  constexpr size_t topic_buffer_size = 17 + ESPHOME_DEVICE_NAME_MAX_LEN + 1;
+  char topic[topic_buffer_size];
+  buf_append_printf(topic, sizeof(topic), 0, "esphome/discover/%s", App.get_name().c_str());
 
   // NOLINTBEGIN(clang-analyzer-cplusplus.NewDeleteLeaks) false positive with ArduinoJson
   this->publish_json(
@@ -500,39 +507,49 @@ bool MQTTClientComponent::publish(const std::string &topic, const std::string &p
 
 bool MQTTClientComponent::publish(const std::string &topic, const char *payload, size_t payload_length, uint8_t qos,
                                   bool retain) {
-  return publish({.topic = topic, .payload = std::string(payload, payload_length), .qos = qos, .retain = retain});
+  return this->publish(topic.c_str(), payload, payload_length, qos, retain);
 }
 
 bool MQTTClientComponent::publish(const MQTTMessage &message) {
+  return this->publish(message.topic.c_str(), message.payload.c_str(), message.payload.length(), message.qos,
+                       message.retain);
+}
+bool MQTTClientComponent::publish_json(const std::string &topic, const json::json_build_t &f, uint8_t qos,
+                                       bool retain) {
+  return this->publish_json(topic.c_str(), f, qos, retain);
+}
+
+bool MQTTClientComponent::publish(const char *topic, const char *payload, size_t payload_length, uint8_t qos,
+                                  bool retain) {
   if (!this->is_connected()) {
-    // critical components will re-transmit their messages
     return false;
   }
-  bool logging_topic = this->log_message_.topic == message.topic;
-  bool ret = this->mqtt_backend_.publish(message);
+  size_t topic_len = strlen(topic);
+  bool logging_topic = (topic_len == this->log_message_.topic.size()) &&
+                       (memcmp(this->log_message_.topic.c_str(), topic, topic_len) == 0);
+  bool ret = this->mqtt_backend_.publish(topic, payload, payload_length, qos, retain);
   delay(0);
   if (!ret && !logging_topic && this->is_connected()) {
     delay(0);
-    ret = this->mqtt_backend_.publish(message);
+    ret = this->mqtt_backend_.publish(topic, payload, payload_length, qos, retain);
     delay(0);
   }
 
   if (!logging_topic) {
     if (ret) {
-      ESP_LOGV(TAG, "Publish(topic='%s' payload='%s' retain=%d qos=%d)", message.topic.c_str(), message.payload.c_str(),
-               message.retain, message.qos);
+      ESP_LOGV(TAG, "Publish(topic='%s' retain=%d qos=%d)", topic, retain, qos);
+      ESP_LOGVV(TAG, "Publish payload (len=%u): '%.*s'", payload_length, static_cast<int>(payload_length), payload);
     } else {
-      ESP_LOGV(TAG, "Publish failed for topic='%s' (len=%u). Will retry", message.topic.c_str(),
-               message.payload.length());
+      ESP_LOGV(TAG, "Publish failed for topic='%s' (len=%u). Will retry", topic, payload_length);
       this->status_momentary_warning("publish", 1000);
     }
   }
   return ret != 0;
 }
-bool MQTTClientComponent::publish_json(const std::string &topic, const json::json_build_t &f, uint8_t qos,
-                                       bool retain) {
+
+bool MQTTClientComponent::publish_json(const char *topic, const json::json_build_t &f, uint8_t qos, bool retain) {
   std::string message = json::build_json(f);
-  return this->publish(topic, message, qos, retain);
+  return this->publish(topic, message.c_str(), message.length(), qos, retain);
 }
 
 void MQTTClientComponent::enable() {
diff --git a/esphome/components/mqtt/mqtt_client.h b/esphome/components/mqtt/mqtt_client.h
index 9e9db03b19..38bc0b4da3 100644
--- a/esphome/components/mqtt/mqtt_client.h
+++ b/esphome/components/mqtt/mqtt_client.h
@@ -229,6 +229,9 @@ class MQTTClientComponent : public Component
   bool publish(const std::string &topic, const char *payload, size_t payload_length, uint8_t qos = 0,
                bool retain = false);
 
+  /// Publish directly without creating MQTTMessage (avoids heap allocation for topic)
+  bool publish(const char *topic, const char *payload, size_t payload_length, uint8_t qos = 0, bool retain = false);
+
   /** Construct and send a JSON MQTT message.
    *
    * @param topic The topic.
@@ -237,6 +240,9 @@ class MQTTClientComponent : public Component
    */
   bool publish_json(const std::string &topic, const json::json_build_t &f, uint8_t qos = 0, bool retain = false);
 
+  /// Publish JSON directly without heap allocation for topic
+  bool publish_json(const char *topic, const json::json_build_t &f, uint8_t qos = 0, bool retain = false);
+
   /// Setup the MQTT client, registering a bunch of callbacks and attempting to connect.
   void setup() override;
   void dump_config() override;

From e88093ca605411cdd5f500c90d888d9ab66428e2 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:38:08 -1000
Subject: [PATCH 10/12] [am43][lightwaverf][rf_bridge][spi_led_strip] Replace
 sprintf with safe alternatives (#13302)

---
 esphome/components/am43/am43_base.cpp          | 18 ++++++------------
 esphome/components/lightwaverf/lightwaverf.cpp |  8 ++++++--
 esphome/components/rf_bridge/rf_bridge.cpp     | 11 ++++++-----
 .../components/spi_led_strip/spi_led_strip.cpp | 14 +++++++-------
 4 files changed, 25 insertions(+), 26 deletions(-)

diff --git a/esphome/components/am43/am43_base.cpp b/esphome/components/am43/am43_base.cpp
index af474dcb79..d70e638382 100644
--- a/esphome/components/am43/am43_base.cpp
+++ b/esphome/components/am43/am43_base.cpp
@@ -1,21 +1,12 @@
 #include "am43_base.h"
+#include "esphome/core/helpers.h"
 #include <cstring>
-#include <cstdio>
 
 namespace esphome {
 namespace am43 {
 
 const uint8_t START_PACKET[5] = {0x00, 0xff, 0x00, 0x00, 0x9a};
 
-std::string pkt_to_hex(const uint8_t *data, uint16_t len) {
-  char buf[64];
-  memset(buf, 0, 64);
-  for (int i = 0; i < len; i++)
-    sprintf(&buf[i * 2], "%02x", data[i]);
-  std::string ret = buf;
-  return ret;
-}
-
 Am43Packet *Am43Encoder::get_battery_level_request() {
   uint8_t data = 0x1;
   return this->encode_(0xA2, &data, 1);
@@ -73,7 +64,9 @@ Am43Packet *Am43Encoder::encode_(uint8_t command, uint8_t *data, uint8_t length)
   memcpy(&this->packet_.data[7], data, length);
   this->packet_.length = length + 7;
   this->checksum_();
-  ESP_LOGV("am43", "ENC(%d): 0x%s", packet_.length, pkt_to_hex(packet_.data, packet_.length).c_str());
+  char hex_buf[format_hex_size(sizeof(this->packet_.data))];
+  ESP_LOGV("am43", "ENC(%d): 0x%s", this->packet_.length,
+           format_hex_to(hex_buf, this->packet_.data, this->packet_.length));
   return &this->packet_;
 }
 
@@ -88,7 +81,8 @@ void Am43Decoder::decode(const uint8_t *data, uint16_t length) {
   this->has_set_state_response_ = false;
   this->has_position_ = false;
   this->has_pin_response_ = false;
-  ESP_LOGV("am43", "DEC(%d): 0x%s", length, pkt_to_hex(data, length).c_str());
+  char hex_buf[format_hex_size(24)];  // Max expected packet size
+  ESP_LOGV("am43", "DEC(%d): 0x%s", length, format_hex_to(hex_buf, data, length));
 
   if (length < 2 || data[0] != 0x9a)
     return;
diff --git a/esphome/components/lightwaverf/lightwaverf.cpp b/esphome/components/lightwaverf/lightwaverf.cpp
index 31ac1fc576..2b44195c97 100644
--- a/esphome/components/lightwaverf/lightwaverf.cpp
+++ b/esphome/components/lightwaverf/lightwaverf.cpp
@@ -1,3 +1,4 @@
+#include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 
 #ifdef USE_ESP8266
@@ -44,13 +45,16 @@ void LightWaveRF::send_rx(const std::vector<uint8_t> &msg, uint8_t repeats, bool
 }
 
 void LightWaveRF::print_msg_(uint8_t *msg, uint8_t len) {
-  char buffer[65];
+#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_DEBUG
+  char buffer[65];  // max 10 entries * 6 chars + null
   ESP_LOGD(TAG, " Received code (len:%i): ", len);
 
+  size_t pos = 0;
   for (int i = 0; i < len; i++) {
-    sprintf(&buffer[i * 6], "0x%02x, ", msg[i]);
+    pos = buf_append_printf(buffer, sizeof(buffer), pos, "0x%02x, ", msg[i]);
   }
   ESP_LOGD(TAG, "[%s]", buffer);
+#endif
 }
 
 void LightWaveRF::dump_config() {
diff --git a/esphome/components/rf_bridge/rf_bridge.cpp b/esphome/components/rf_bridge/rf_bridge.cpp
index 52ce037dbe..8105767485 100644
--- a/esphome/components/rf_bridge/rf_bridge.cpp
+++ b/esphome/components/rf_bridge/rf_bridge.cpp
@@ -1,6 +1,7 @@
 #include "rf_bridge.h"
-#include "esphome/core/log.h"
 #include "esphome/core/application.h"
+#include "esphome/core/helpers.h"
+#include "esphome/core/log.h"
 #include <cinttypes>
 #include <cstring>
 
@@ -72,9 +73,9 @@ bool RFBridgeComponent::parse_bridge_byte_(uint8_t byte) {
 
       data.length = raw[2];
       data.protocol = raw[3];
-      char next_byte[3];
+      char next_byte[3];  // 2 hex chars + null
       for (uint8_t i = 0; i < data.length - 1; i++) {
-        sprintf(next_byte, "%02X", raw[4 + i]);
+        buf_append_printf(next_byte, sizeof(next_byte), 0, "%02X", raw[4 + i]);
         data.code += next_byte;
       }
 
@@ -90,10 +91,10 @@ bool RFBridgeComponent::parse_bridge_byte_(uint8_t byte) {
 
       uint8_t buckets = raw[2] << 1;
       std::string str;
-      char next_byte[3];
+      char next_byte[3];  // 2 hex chars + null
 
       for (uint32_t i = 0; i <= at; i++) {
-        sprintf(next_byte, "%02X", raw[i]);
+        buf_append_printf(next_byte, sizeof(next_byte), 0, "%02X", raw[i]);
         str += next_byte;
         if ((i > 3) && buckets) {
           buckets--;
diff --git a/esphome/components/spi_led_strip/spi_led_strip.cpp b/esphome/components/spi_led_strip/spi_led_strip.cpp
index afb51afe3a..ff8d2e6ee0 100644
--- a/esphome/components/spi_led_strip/spi_led_strip.cpp
+++ b/esphome/components/spi_led_strip/spi_led_strip.cpp
@@ -1,4 +1,5 @@
 #include "spi_led_strip.h"
+#include "esphome/core/helpers.h"
 
 namespace esphome {
 namespace spi_led_strip {
@@ -47,15 +48,14 @@ void SpiLedStrip::dump_config() {
 void SpiLedStrip::write_state(light::LightState *state) {
   if (this->is_failed())
     return;
-  if (ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE) {
-    char strbuf[49];
-    size_t len = std::min(this->buffer_size_, (size_t) (sizeof(strbuf) - 1) / 3);
-    memset(strbuf, 0, sizeof(strbuf));
-    for (size_t i = 0; i != len; i++) {
-      sprintf(strbuf + i * 3, "%02X ", this->buf_[i]);
-    }
+#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
+  {
+    char strbuf[49];  // format_hex_pretty_size(16) = 48, fits 16 bytes
+    size_t len = std::min(this->buffer_size_, (size_t) 16);
+    format_hex_pretty_to(strbuf, sizeof(strbuf), this->buf_, len, ' ');
     esph_log_v(TAG, "write_state: buf = %s", strbuf);
   }
+#endif
   this->enable();
   this->write_array(this->buf_, this->buffer_size_);
   this->disable();

From 5d7b38b26164940883c2d45715d20b85cb7de874 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:38:22 -1000
Subject: [PATCH 11/12] [ezo_pmp] Replace sprintf with bounds-checked snprintf
 (#13304)

---
 esphome/components/ezo_pmp/ezo_pmp.cpp | 47 ++++++++++++++------------
 1 file changed, 25 insertions(+), 22 deletions(-)

diff --git a/esphome/components/ezo_pmp/ezo_pmp.cpp b/esphome/components/ezo_pmp/ezo_pmp.cpp
index 61b601328a..9d2f4fc687 100644
--- a/esphome/components/ezo_pmp/ezo_pmp.cpp
+++ b/esphome/components/ezo_pmp/ezo_pmp.cpp
@@ -318,90 +318,93 @@ void EzoPMP::send_next_command_() {
   switch (this->next_command_) {
     // Read Commands
     case EZO_PMP_COMMAND_READ_DOSING:  // Page 54
-      command_buffer_length = sprintf((char *) command_buffer, "D,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "D,?");
       break;
 
     case EZO_PMP_COMMAND_READ_SINGLE_REPORT:  // Single Report (page 53)
-      command_buffer_length = sprintf((char *) command_buffer, "R");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "R");
       break;
 
     case EZO_PMP_COMMAND_READ_MAX_FLOW_RATE:
-      command_buffer_length = sprintf((char *) command_buffer, "DC,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "DC,?");
       break;
 
     case EZO_PMP_COMMAND_READ_PAUSE_STATUS:
-      command_buffer_length = sprintf((char *) command_buffer, "P,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "P,?");
       break;
 
     case EZO_PMP_COMMAND_READ_TOTAL_VOLUME_DOSED:
-      command_buffer_length = sprintf((char *) command_buffer, "TV,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "TV,?");
       break;
 
     case EZO_PMP_COMMAND_READ_ABSOLUTE_TOTAL_VOLUME_DOSED:
-      command_buffer_length = sprintf((char *) command_buffer, "ATV,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "ATV,?");
       break;
 
     case EZO_PMP_COMMAND_READ_CALIBRATION_STATUS:
-      command_buffer_length = sprintf((char *) command_buffer, "Cal,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "Cal,?");
       break;
 
     case EZO_PMP_COMMAND_READ_PUMP_VOLTAGE:
-      command_buffer_length = sprintf((char *) command_buffer, "PV,?");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "PV,?");
       break;
 
       // Non-Read Commands
 
     case EZO_PMP_COMMAND_FIND:  // Find (page 52)
-      command_buffer_length = sprintf((char *) command_buffer, "Find");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "Find");
       wait_time_for_command = 60000;  // This command will block all updates for a minute
       break;
 
     case EZO_PMP_COMMAND_DOSE_CONTINUOUSLY:  // Continuous Dispensing (page 54)
-      command_buffer_length = sprintf((char *) command_buffer, "D,*");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "D,*");
       break;
 
     case EZO_PMP_COMMAND_CLEAR_TOTAL_VOLUME_DOSED:  // Clear Total Volume Dosed (page 64)
-      command_buffer_length = sprintf((char *) command_buffer, "Clear");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "Clear");
       break;
 
     case EZO_PMP_COMMAND_CLEAR_CALIBRATION:  // Clear Calibration (page 65)
-      command_buffer_length = sprintf((char *) command_buffer, "Cal,clear");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "Cal,clear");
       break;
 
     case EZO_PMP_COMMAND_PAUSE_DOSING:  // Pause (page 61)
-      command_buffer_length = sprintf((char *) command_buffer, "P");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "P");
       break;
 
     case EZO_PMP_COMMAND_STOP_DOSING:  // Stop (page 62)
-      command_buffer_length = sprintf((char *) command_buffer, "X");
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "X");
       break;
 
       // Non-Read commands with parameters
 
     case EZO_PMP_COMMAND_DOSE_VOLUME:  // Volume Dispensing (page 55)
-      command_buffer_length = sprintf((char *) command_buffer, "D,%0.1f", this->next_command_volume_);
+      command_buffer_length =
+          snprintf((char *) command_buffer, sizeof(command_buffer), "D,%0.1f", this->next_command_volume_);
       break;
 
     case EZO_PMP_COMMAND_DOSE_VOLUME_OVER_TIME:  // Dose over time (page 56)
-      command_buffer_length =
-          sprintf((char *) command_buffer, "D,%0.1f,%i", this->next_command_volume_, this->next_command_duration_);
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "D,%0.1f,%i",
+                                       this->next_command_volume_, this->next_command_duration_);
       break;
 
     case EZO_PMP_COMMAND_DOSE_WITH_CONSTANT_FLOW_RATE:  // Constant Flow Rate (page 57)
-      command_buffer_length =
-          sprintf((char *) command_buffer, "DC,%0.1f,%i", this->next_command_volume_, this->next_command_duration_);
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "DC,%0.1f,%i",
+                                       this->next_command_volume_, this->next_command_duration_);
       break;
 
     case EZO_PMP_COMMAND_SET_CALIBRATION_VOLUME:  // Set Calibration Volume (page 65)
-      command_buffer_length = sprintf((char *) command_buffer, "Cal,%0.2f", this->next_command_volume_);
+      command_buffer_length =
+          snprintf((char *) command_buffer, sizeof(command_buffer), "Cal,%0.2f", this->next_command_volume_);
       break;
 
     case EZO_PMP_COMMAND_CHANGE_I2C_ADDRESS:  // Change I2C Address (page 73)
-      command_buffer_length = sprintf((char *) command_buffer, "I2C,%i", this->next_command_duration_);
+      command_buffer_length =
+          snprintf((char *) command_buffer, sizeof(command_buffer), "I2C,%i", this->next_command_duration_);
       break;
 
     case EZO_PMP_COMMAND_EXEC_ARBITRARY_COMMAND_ADDRESS:  // Run an arbitrary command
-      command_buffer_length = sprintf((char *) command_buffer, this->arbitrary_command_, this->next_command_duration_);
+      command_buffer_length = snprintf((char *) command_buffer, sizeof(command_buffer), "%s", this->arbitrary_command_);
       ESP_LOGI(TAG, "Sending arbitrary command: %s", (char *) command_buffer);
       break;
 

From ea70faf642e12f6d6cab14b70cee6861bda1cdc0 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 19 Jan 2026 17:38:56 -1000
Subject: [PATCH 12/12] [debug] Use shared buf_append_printf helper from core
 (#13260)

---
 esphome/components/debug/debug_component.cpp |  2 +-
 esphome/components/debug/debug_component.h   | 41 +-------------------
 esphome/components/debug/debug_esp32.cpp     | 30 +++++++-------
 esphome/components/debug/debug_esp8266.cpp   | 22 +++++------
 esphome/components/debug/debug_libretiny.cpp | 12 +++---
 esphome/components/debug/debug_rp2040.cpp    |  2 +-
 esphome/components/debug/debug_zephyr.cpp    | 20 +++++-----
 7 files changed, 45 insertions(+), 84 deletions(-)

diff --git a/esphome/components/debug/debug_component.cpp b/esphome/components/debug/debug_component.cpp
index ae38fb2ccd..15f68c3a3b 100644
--- a/esphome/components/debug/debug_component.cpp
+++ b/esphome/components/debug/debug_component.cpp
@@ -30,7 +30,7 @@ void DebugComponent::dump_config() {
 
   char device_info_buffer[DEVICE_INFO_BUFFER_SIZE];
   ESP_LOGD(TAG, "ESPHome version %s", ESPHOME_VERSION);
-  size_t pos = buf_append(device_info_buffer, DEVICE_INFO_BUFFER_SIZE, 0, "%s", ESPHOME_VERSION);
+  size_t pos = buf_append_printf(device_info_buffer, DEVICE_INFO_BUFFER_SIZE, 0, "%s", ESPHOME_VERSION);
 
   this->free_heap_ = get_free_heap_();
   ESP_LOGD(TAG, "Free Heap Size: %" PRIu32 " bytes", this->free_heap_);
diff --git a/esphome/components/debug/debug_component.h b/esphome/components/debug/debug_component.h
index 6cf52d890c..e4f4bb36eb 100644
--- a/esphome/components/debug/debug_component.h
+++ b/esphome/components/debug/debug_component.h
@@ -5,12 +5,6 @@
 #include "esphome/core/helpers.h"
 #include "esphome/core/macros.h"
 #include <span>
-#include <cstdarg>
-#include <cstdio>
-#include <algorithm>
-#ifdef USE_ESP8266
-#include <pgmspace.h>
-#endif
 
 #ifdef USE_SENSOR
 #include "esphome/components/sensor/sensor.h"
@@ -25,40 +19,7 @@ namespace debug {
 static constexpr size_t DEVICE_INFO_BUFFER_SIZE = 256;
 static constexpr size_t RESET_REASON_BUFFER_SIZE = 128;
 
-#ifdef USE_ESP8266
-// ESP8266: Use vsnprintf_P to keep format strings in flash (PROGMEM)
-// Format strings must be wrapped with PSTR() macro
-inline size_t buf_append_p(char *buf, size_t size, size_t pos, PGM_P fmt, ...) {
-  if (pos >= size) {
-    return size;
-  }
-  va_list args;
-  va_start(args, fmt);
-  int written = vsnprintf_P(buf + pos, size - pos, fmt, args);
-  va_end(args);
-  if (written < 0) {
-    return pos;  // encoding error
-  }
-  return std::min(pos + static_cast<size_t>(written), size);
-}
-#define buf_append(buf, size, pos, fmt, ...) buf_append_p(buf, size, pos, PSTR(fmt), ##__VA_ARGS__)
-#else
-/// Safely append formatted string to buffer, returning new position (capped at size)
-__attribute__((format(printf, 4, 5))) inline size_t buf_append(char *buf, size_t size, size_t pos, const char *fmt,
-                                                               ...) {
-  if (pos >= size) {
-    return size;
-  }
-  va_list args;
-  va_start(args, fmt);
-  int written = vsnprintf(buf + pos, size - pos, fmt, args);
-  va_end(args);
-  if (written < 0) {
-    return pos;  // encoding error
-  }
-  return std::min(pos + static_cast<size_t>(written), size);
-}
-#endif
+// buf_append_printf is now provided by esphome/core/helpers.h
 
 class DebugComponent : public PollingComponent {
  public:
diff --git a/esphome/components/debug/debug_esp32.cpp b/esphome/components/debug/debug_esp32.cpp
index 8c41011f7d..aad4c7426c 100644
--- a/esphome/components/debug/debug_esp32.cpp
+++ b/esphome/components/debug/debug_esp32.cpp
@@ -173,8 +173,8 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
   uint32_t flash_size = ESP.getFlashChipSize() / 1024;       // NOLINT
   uint32_t flash_speed = ESP.getFlashChipSpeed() / 1000000;  // NOLINT
   ESP_LOGD(TAG, "Flash Chip: Size=%" PRIu32 "kB Speed=%" PRIu32 "MHz Mode=%s", flash_size, flash_speed, flash_mode);
-  pos = buf_append(buf, size, pos, "|Flash: %" PRIu32 "kB Speed:%" PRIu32 "MHz Mode:%s", flash_size, flash_speed,
-                   flash_mode);
+  pos = buf_append_printf(buf, size, pos, "|Flash: %" PRIu32 "kB Speed:%" PRIu32 "MHz Mode:%s", flash_size, flash_speed,
+                          flash_mode);
 #endif
 
   esp_chip_info_t info;
@@ -182,52 +182,52 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
   const char *model = ESPHOME_VARIANT;
 
   // Build features string
-  pos = buf_append(buf, size, pos, "|Chip: %s Features:", model);
+  pos = buf_append_printf(buf, size, pos, "|Chip: %s Features:", model);
   bool first_feature = true;
   for (const auto &feature : CHIP_FEATURES) {
     if (info.features & feature.bit) {
-      pos = buf_append(buf, size, pos, "%s%s", first_feature ? "" : ", ", feature.name);
+      pos = buf_append_printf(buf, size, pos, "%s%s", first_feature ? "" : ", ", feature.name);
       first_feature = false;
       info.features &= ~feature.bit;
     }
   }
   if (info.features != 0) {
-    pos = buf_append(buf, size, pos, "%sOther:0x%" PRIx32, first_feature ? "" : ", ", info.features);
+    pos = buf_append_printf(buf, size, pos, "%sOther:0x%" PRIx32, first_feature ? "" : ", ", info.features);
   }
   ESP_LOGD(TAG, "Chip: Model=%s, Cores=%u, Revision=%u", model, info.cores, info.revision);
-  pos = buf_append(buf, size, pos, " Cores:%u Revision:%u", info.cores, info.revision);
+  pos = buf_append_printf(buf, size, pos, " Cores:%u Revision:%u", info.cores, info.revision);
 
   uint32_t cpu_freq_mhz = arch_get_cpu_freq_hz() / 1000000;
   ESP_LOGD(TAG, "CPU Frequency: %" PRIu32 " MHz", cpu_freq_mhz);
-  pos = buf_append(buf, size, pos, "|CPU Frequency: %" PRIu32 " MHz", cpu_freq_mhz);
+  pos = buf_append_printf(buf, size, pos, "|CPU Frequency: %" PRIu32 " MHz", cpu_freq_mhz);
 
   // Framework detection
 #ifdef USE_ARDUINO
   ESP_LOGD(TAG, "Framework: Arduino");
-  pos = buf_append(buf, size, pos, "|Framework: Arduino");
+  pos = buf_append_printf(buf, size, pos, "|Framework: Arduino");
 #elif defined(USE_ESP32)
   ESP_LOGD(TAG, "Framework: ESP-IDF");
-  pos = buf_append(buf, size, pos, "|Framework: ESP-IDF");
+  pos = buf_append_printf(buf, size, pos, "|Framework: ESP-IDF");
 #else
   ESP_LOGW(TAG, "Framework: UNKNOWN");
-  pos = buf_append(buf, size, pos, "|Framework: UNKNOWN");
+  pos = buf_append_printf(buf, size, pos, "|Framework: UNKNOWN");
 #endif
 
   ESP_LOGD(TAG, "ESP-IDF Version: %s", esp_get_idf_version());
-  pos = buf_append(buf, size, pos, "|ESP-IDF: %s", esp_get_idf_version());
+  pos = buf_append_printf(buf, size, pos, "|ESP-IDF: %s", esp_get_idf_version());
 
   uint8_t mac[6];
   get_mac_address_raw(mac);
   ESP_LOGD(TAG, "EFuse MAC: %02X:%02X:%02X:%02X:%02X:%02X", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
-  pos = buf_append(buf, size, pos, "|EFuse MAC: %02X:%02X:%02X:%02X:%02X:%02X", mac[0], mac[1], mac[2], mac[3], mac[4],
-                   mac[5]);
+  pos = buf_append_printf(buf, size, pos, "|EFuse MAC: %02X:%02X:%02X:%02X:%02X:%02X", mac[0], mac[1], mac[2], mac[3],
+                          mac[4], mac[5]);
 
   char reason_buffer[RESET_REASON_BUFFER_SIZE];
   const char *reset_reason = get_reset_reason_(std::span<char, RESET_REASON_BUFFER_SIZE>(reason_buffer));
-  pos = buf_append(buf, size, pos, "|Reset: %s", reset_reason);
+  pos = buf_append_printf(buf, size, pos, "|Reset: %s", reset_reason);
 
   const char *wakeup_cause = get_wakeup_cause_(std::span<char, RESET_REASON_BUFFER_SIZE>(reason_buffer));
-  pos = buf_append(buf, size, pos, "|Wakeup: %s", wakeup_cause);
+  pos = buf_append_printf(buf, size, pos, "|Wakeup: %s", wakeup_cause);
 
   return pos;
 }
diff --git a/esphome/components/debug/debug_esp8266.cpp b/esphome/components/debug/debug_esp8266.cpp
index 274f77e20d..19f15d7d98 100644
--- a/esphome/components/debug/debug_esp8266.cpp
+++ b/esphome/components/debug/debug_esp8266.cpp
@@ -53,8 +53,8 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
   uint32_t flash_size = ESP.getFlashChipSize() / 1024;       // NOLINT
   uint32_t flash_speed = ESP.getFlashChipSpeed() / 1000000;  // NOLINT
   ESP_LOGD(TAG, "Flash Chip: Size=%" PRIu32 "kB Speed=%" PRIu32 "MHz Mode=%s", flash_size, flash_speed, flash_mode);
-  pos = buf_append(buf, size, pos, "|Flash: %" PRIu32 "kB Speed:%" PRIu32 "MHz Mode:%s", flash_size, flash_speed,
-                   flash_mode);
+  pos = buf_append_printf(buf, size, pos, "|Flash: %" PRIu32 "kB Speed:%" PRIu32 "MHz Mode:%s", flash_size, flash_speed,
+                          flash_mode);
 
 #if !defined(CLANG_TIDY)
   char reason_buffer[RESET_REASON_BUFFER_SIZE];
@@ -77,15 +77,15 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
            chip_id, ESP.getSdkVersion(), ESP.getCoreVersion().c_str(), boot_version, boot_mode, cpu_freq, flash_chip_id,
            reset_reason, ESP.getResetInfo().c_str());
 
-  pos = buf_append(buf, size, pos, "|Chip: 0x%08" PRIX32, chip_id);
-  pos = buf_append(buf, size, pos, "|SDK: %s", ESP.getSdkVersion());
-  pos = buf_append(buf, size, pos, "|Core: %s", ESP.getCoreVersion().c_str());
-  pos = buf_append(buf, size, pos, "|Boot: %u", boot_version);
-  pos = buf_append(buf, size, pos, "|Mode: %u", boot_mode);
-  pos = buf_append(buf, size, pos, "|CPU: %u", cpu_freq);
-  pos = buf_append(buf, size, pos, "|Flash: 0x%08" PRIX32, flash_chip_id);
-  pos = buf_append(buf, size, pos, "|Reset: %s", reset_reason);
-  pos = buf_append(buf, size, pos, "|%s", ESP.getResetInfo().c_str());
+  pos = buf_append_printf(buf, size, pos, "|Chip: 0x%08" PRIX32, chip_id);
+  pos = buf_append_printf(buf, size, pos, "|SDK: %s", ESP.getSdkVersion());
+  pos = buf_append_printf(buf, size, pos, "|Core: %s", ESP.getCoreVersion().c_str());
+  pos = buf_append_printf(buf, size, pos, "|Boot: %u", boot_version);
+  pos = buf_append_printf(buf, size, pos, "|Mode: %u", boot_mode);
+  pos = buf_append_printf(buf, size, pos, "|CPU: %u", cpu_freq);
+  pos = buf_append_printf(buf, size, pos, "|Flash: 0x%08" PRIX32, flash_chip_id);
+  pos = buf_append_printf(buf, size, pos, "|Reset: %s", reset_reason);
+  pos = buf_append_printf(buf, size, pos, "|%s", ESP.getResetInfo().c_str());
 #endif
 
   return pos;
diff --git a/esphome/components/debug/debug_libretiny.cpp b/esphome/components/debug/debug_libretiny.cpp
index aae27c8ca2..14bbdb945a 100644
--- a/esphome/components/debug/debug_libretiny.cpp
+++ b/esphome/components/debug/debug_libretiny.cpp
@@ -36,12 +36,12 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
            lt_get_version(), lt_cpu_get_model_name(), lt_cpu_get_model(), lt_cpu_get_freq_mhz(), mac_id,
            lt_get_board_code(), flash_kib, ram_kib, reset_reason);
 
-  pos = buf_append(buf, size, pos, "|Version: %s", LT_BANNER_STR + 10);
-  pos = buf_append(buf, size, pos, "|Reset Reason: %s", reset_reason);
-  pos = buf_append(buf, size, pos, "|Chip Name: %s", lt_cpu_get_model_name());
-  pos = buf_append(buf, size, pos, "|Chip ID: 0x%06" PRIX32, mac_id);
-  pos = buf_append(buf, size, pos, "|Flash: %" PRIu32 " KiB", flash_kib);
-  pos = buf_append(buf, size, pos, "|RAM: %" PRIu32 " KiB", ram_kib);
+  pos = buf_append_printf(buf, size, pos, "|Version: %s", LT_BANNER_STR + 10);
+  pos = buf_append_printf(buf, size, pos, "|Reset Reason: %s", reset_reason);
+  pos = buf_append_printf(buf, size, pos, "|Chip Name: %s", lt_cpu_get_model_name());
+  pos = buf_append_printf(buf, size, pos, "|Chip ID: 0x%06" PRIX32, mac_id);
+  pos = buf_append_printf(buf, size, pos, "|Flash: %" PRIu32 " KiB", flash_kib);
+  pos = buf_append_printf(buf, size, pos, "|RAM: %" PRIu32 " KiB", ram_kib);
 
   return pos;
 }
diff --git a/esphome/components/debug/debug_rp2040.cpp b/esphome/components/debug/debug_rp2040.cpp
index a426a73bc2..c9d41942db 100644
--- a/esphome/components/debug/debug_rp2040.cpp
+++ b/esphome/components/debug/debug_rp2040.cpp
@@ -19,7 +19,7 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
 
   uint32_t cpu_freq = rp2040.f_cpu();
   ESP_LOGD(TAG, "CPU Frequency: %" PRIu32, cpu_freq);
-  pos = buf_append(buf, size, pos, "|CPU Frequency: %" PRIu32, cpu_freq);
+  pos = buf_append_printf(buf, size, pos, "|CPU Frequency: %" PRIu32, cpu_freq);
 
   return pos;
 }
diff --git a/esphome/components/debug/debug_zephyr.cpp b/esphome/components/debug/debug_zephyr.cpp
index 3f9af03b2b..6a88522b0d 100644
--- a/esphome/components/debug/debug_zephyr.cpp
+++ b/esphome/components/debug/debug_zephyr.cpp
@@ -20,9 +20,9 @@ static size_t append_reset_reason(char *buf, size_t size, size_t pos, bool set,
     return pos;
   }
   if (pos > 0) {
-    pos = buf_append(buf, size, pos, ", ");
+    pos = buf_append_printf(buf, size, pos, ", ");
   }
-  return buf_append(buf, size, pos, "%s", reason);
+  return buf_append_printf(buf, size, pos, "%s", reason);
 }
 
 static inline uint32_t read_mem_u32(uintptr_t addr) {
@@ -140,7 +140,7 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
   const char *supply_status =
       (nrf_power_mainregstatus_get(NRF_POWER) == NRF_POWER_MAINREGSTATUS_NORMAL) ? "Normal voltage." : "High voltage.";
   ESP_LOGD(TAG, "Main supply status: %s", supply_status);
-  pos = buf_append(buf, size, pos, "|Main supply status: %s", supply_status);
+  pos = buf_append_printf(buf, size, pos, "|Main supply status: %s", supply_status);
 
   // Regulator stage 0
   if (nrf_power_mainregstatus_get(NRF_POWER) == NRF_POWER_MAINREGSTATUS_HIGH) {
@@ -172,16 +172,16 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
         reg0_voltage = "???V";
     }
     ESP_LOGD(TAG, "Regulator stage 0: %s, %s", reg0_type, reg0_voltage);
-    pos = buf_append(buf, size, pos, "|Regulator stage 0: %s, %s", reg0_type, reg0_voltage);
+    pos = buf_append_printf(buf, size, pos, "|Regulator stage 0: %s, %s", reg0_type, reg0_voltage);
   } else {
     ESP_LOGD(TAG, "Regulator stage 0: disabled");
-    pos = buf_append(buf, size, pos, "|Regulator stage 0: disabled");
+    pos = buf_append_printf(buf, size, pos, "|Regulator stage 0: disabled");
   }
 
   // Regulator stage 1
   const char *reg1_type = nrf_power_dcdcen_get(NRF_POWER) ? "DC/DC" : "LDO";
   ESP_LOGD(TAG, "Regulator stage 1: %s", reg1_type);
-  pos = buf_append(buf, size, pos, "|Regulator stage 1: %s", reg1_type);
+  pos = buf_append_printf(buf, size, pos, "|Regulator stage 1: %s", reg1_type);
 
   // USB power state
   const char *usb_state;
@@ -195,7 +195,7 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
     usb_state = "disconnected";
   }
   ESP_LOGD(TAG, "USB power state: %s", usb_state);
-  pos = buf_append(buf, size, pos, "|USB power state: %s", usb_state);
+  pos = buf_append_printf(buf, size, pos, "|USB power state: %s", usb_state);
 
   // Power-fail comparator
   bool enabled;
@@ -300,14 +300,14 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
           break;
       }
       ESP_LOGD(TAG, "Power-fail comparator: %s, VDDH: %s", pof_voltage, vddh_voltage);
-      pos = buf_append(buf, size, pos, "|Power-fail comparator: %s, VDDH: %s", pof_voltage, vddh_voltage);
+      pos = buf_append_printf(buf, size, pos, "|Power-fail comparator: %s, VDDH: %s", pof_voltage, vddh_voltage);
     } else {
       ESP_LOGD(TAG, "Power-fail comparator: %s", pof_voltage);
-      pos = buf_append(buf, size, pos, "|Power-fail comparator: %s", pof_voltage);
+      pos = buf_append_printf(buf, size, pos, "|Power-fail comparator: %s", pof_voltage);
     }
   } else {
     ESP_LOGD(TAG, "Power-fail comparator: disabled");
-    pos = buf_append(buf, size, pos, "|Power-fail comparator: disabled");
+    pos = buf_append_printf(buf, size, pos, "|Power-fail comparator: disabled");
   }
 
   auto package = [](uint32_t value) {