diff --git a/esphome/components/anova/anova_base.cpp b/esphome/components/anova/anova_base.cpp
index fef4f1d8526..a14dd728a80 100644
--- a/esphome/components/anova/anova_base.cpp
+++ b/esphome/components/anova/anova_base.cpp
@@ -2,6 +2,8 @@
 #include <cstdio>
 #include <cstring>
 
+#include "esphome/core/alloc_helpers.h"
+
 namespace esphome {
 namespace anova {
 
@@ -105,14 +107,14 @@ void AnovaCodec::decode(const uint8_t *data, uint16_t length) {
     }
     case READ_TARGET_TEMPERATURE:
     case SET_TARGET_TEMPERATURE: {
-      this->target_temp_ = parse_number<float>(str_until(buf, '\r')).value_or(0.0f);
+      this->target_temp_ = parse_number<float>(str_until(buf, '\r')).value_or(0.0f);  // NOLINT
       if (this->fahrenheit_)
         this->target_temp_ = ftoc(this->target_temp_);
       this->has_target_temp_ = true;
       break;
     }
     case READ_CURRENT_TEMPERATURE: {
-      this->current_temp_ = parse_number<float>(str_until(buf, '\r')).value_or(0.0f);
+      this->current_temp_ = parse_number<float>(str_until(buf, '\r')).value_or(0.0f);  // NOLINT
       if (this->fahrenheit_)
         this->current_temp_ = ftoc(this->current_temp_);
       this->has_current_temp_ = true;
diff --git a/esphome/components/http_request/http_request.cpp b/esphome/components/http_request/http_request.cpp
index 2c74638f12c..d45208ed5df 100644
--- a/esphome/components/http_request/http_request.cpp
+++ b/esphome/components/http_request/http_request.cpp
@@ -22,7 +22,7 @@ void HttpRequestComponent::dump_config() {
 }
 
 std::string HttpContainer::get_response_header(const std::string &header_name) {
-  auto lower = str_lower_case(header_name);
+  auto lower = str_lower_case(header_name);  // NOLINT
   for (const auto &entry : this->response_headers_) {
     if (entry.name == lower) {
       ESP_LOGD(TAG, "Header with name %s found with value %s", lower.c_str(), entry.value.c_str());
diff --git a/esphome/components/http_request/http_request.h b/esphome/components/http_request/http_request.h
index ae73983bab2..f37bf776333 100644
--- a/esphome/components/http_request/http_request.h
+++ b/esphome/components/http_request/http_request.h
@@ -11,6 +11,7 @@
 #include "esphome/core/automation.h"
 #include "esphome/core/component.h"
 #include "esphome/core/defines.h"
+#include "esphome/core/alloc_helpers.h"
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 
@@ -400,7 +401,7 @@ class HttpRequestComponent : public Component {
     std::vector<std::string> lower;
     lower.reserve(collect_headers.size());
     for (const auto &h : collect_headers) {
-      lower.push_back(str_lower_case(h));
+      lower.push_back(str_lower_case(h));  // NOLINT
     }
     return this->perform(url, method, body, request_headers, lower);
   }
@@ -415,7 +416,7 @@ class HttpRequestComponent : public Component {
     std::vector<std::string> lower;
     lower.reserve(collect_headers.size());
     for (const auto &h : collect_headers) {
-      lower.push_back(str_lower_case(h));
+      lower.push_back(str_lower_case(h));  // NOLINT
     }
     return this->perform(url, method, body, std::vector<Header>(request_headers.begin(), request_headers.end()), lower);
   }
diff --git a/esphome/components/http_request/http_request_arduino.cpp b/esphome/components/http_request/http_request_arduino.cpp
index f0dd6492852..05f9db1c069 100644
--- a/esphome/components/http_request/http_request_arduino.cpp
+++ b/esphome/components/http_request/http_request_arduino.cpp
@@ -161,7 +161,7 @@ std::shared_ptr<HttpContainer> HttpRequestArduino::perform(const std::string &ur
   container->response_headers_.clear();
   auto header_count = container->client_.headers();
   for (int i = 0; i < header_count; i++) {
-    const std::string header_name = str_lower_case(container->client_.headerName(i).c_str());
+    const std::string header_name = str_lower_case(container->client_.headerName(i).c_str());  // NOLINT
     if (should_collect_header(lower_case_collect_headers, header_name)) {
       std::string header_value = container->client_.header(i).c_str();
       ESP_LOGD(TAG, "Received response header, name: %s, value: %s", header_name.c_str(), header_value.c_str());
diff --git a/esphome/components/http_request/http_request_host.cpp b/esphome/components/http_request/http_request_host.cpp
index 60ab4d68a04..85c6e8b3c7b 100644
--- a/esphome/components/http_request/http_request_host.cpp
+++ b/esphome/components/http_request/http_request_host.cpp
@@ -115,7 +115,7 @@ std::shared_ptr<HttpContainer> HttpRequestHost::perform(const std::string &url,
   container->content_length = container->response_body_.size();
   for (auto header : response.headers) {
     ESP_LOGD(TAG, "Header: %s: %s", header.first.c_str(), header.second.c_str());
-    auto lower_name = str_lower_case(header.first);
+    auto lower_name = str_lower_case(header.first);  // NOLINT
     if (should_collect_header(lower_case_collect_headers, lower_name)) {
       container->response_headers_.push_back({lower_name, header.second});
     }
diff --git a/esphome/components/http_request/http_request_idf.cpp b/esphome/components/http_request/http_request_idf.cpp
index 30f53eecdc7..3e341395a46 100644
--- a/esphome/components/http_request/http_request_idf.cpp
+++ b/esphome/components/http_request/http_request_idf.cpp
@@ -38,7 +38,7 @@ esp_err_t HttpRequestIDF::http_event_handler(esp_http_client_event_t *evt) {
 
   switch (evt->event_id) {
     case HTTP_EVENT_ON_HEADER: {
-      const std::string header_name = str_lower_case(evt->header_key);
+      const std::string header_name = str_lower_case(evt->header_key);  // NOLINT
       if (should_collect_header(user_data->lower_case_collect_headers, header_name)) {
         const std::string header_value = evt->header_value;
         ESP_LOGD(TAG, "Received response header, name: %s, value: %s", header_name.c_str(), header_value.c_str());
diff --git a/esphome/core/alloc_helpers.cpp b/esphome/core/alloc_helpers.cpp
new file mode 100644
index 00000000000..11c7abe3f7b
--- /dev/null
+++ b/esphome/core/alloc_helpers.cpp
@@ -0,0 +1,229 @@
+#include "esphome/core/alloc_helpers.h"
+
+#include "esphome/core/helpers.h"
+
+#include <algorithm>
+#include <cctype>
+#include <cstdarg>
+#include <cstdio>
+#include <cstring>
+#include <string>
+
+namespace esphome {
+
+// --- String helpers ---
+
+std::string str_truncate(const std::string &str, size_t length) {
+  return str.length() > length ? str.substr(0, length) : str;
+}
+
+std::string str_until(const char *str, char ch) {
+  const char *pos = strchr(str, ch);
+  return pos == nullptr ? std::string(str) : std::string(str, pos - str);
+}
+std::string str_until(const std::string &str, char ch) { return str.substr(0, str.find(ch)); }
+
+// wrapper around std::transform to run safely on functions from the ctype.h header
+// see https://en.cppreference.com/w/cpp/string/byte/toupper#Notes
+template<int (*fn)(int)> std::string str_ctype_transform(const std::string &str) {
+  std::string result;
+  result.resize(str.length());
+  std::transform(str.begin(), str.end(), result.begin(), [](unsigned char ch) { return fn(ch); });
+  return result;
+}
+std::string str_lower_case(const std::string &str) { return str_ctype_transform<std::tolower>(str); }
+
+std::string str_upper_case(const std::string &str) {
+  std::string result;
+  result.resize(str.length());
+  std::transform(str.begin(), str.end(), result.begin(), [](unsigned char ch) { return std::toupper(ch); });
+  return result;
+}
+
+std::string str_snake_case(const std::string &str) {
+  std::string result = str;
+  for (char &c : result) {
+    c = to_snake_case_char(c);
+  }
+  return result;
+}
+
+std::string str_sanitize(const std::string &str) {
+  std::string result;
+  result.resize(str.size());
+  str_sanitize_to(&result[0], str.size() + 1, str.c_str());
+  return result;
+}
+
+std::string str_snprintf(const char *fmt, size_t len, ...) {
+  std::string str;
+  va_list args;
+
+  str.resize(len);
+  va_start(args, len);
+  size_t out_length = vsnprintf(&str[0], len + 1, fmt, args);
+  va_end(args);
+
+  if (out_length < len)
+    str.resize(out_length);
+
+  return str;
+}
+
+std::string str_sprintf(const char *fmt, ...) {
+  std::string str;
+  va_list args;
+
+  va_start(args, fmt);
+  size_t length = vsnprintf(nullptr, 0, fmt, args);
+  va_end(args);
+
+  str.resize(length);
+  va_start(args, fmt);
+  vsnprintf(&str[0], length + 1, fmt, args);
+  va_end(args);
+
+  return str;
+}
+
+// --- Value formatting helpers ---
+
+std::string value_accuracy_to_string(float value, int8_t accuracy_decimals) {
+  char buf[VALUE_ACCURACY_MAX_LEN];
+  value_accuracy_to_buf(buf, value, accuracy_decimals);
+  return std::string(buf);
+}
+
+// --- Base64 helpers ---
+
+static constexpr const char *BASE64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+                                            "abcdefghijklmnopqrstuvwxyz"
+                                            "0123456789+/";
+
+// Encode 3 input bytes to 4 base64 characters, append 'count' to ret.
+static inline void base64_encode_triple(const char *char_array_3, int count, std::string &ret) {
+  char char_array_4[4];
+  char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
+  char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
+  char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
+  char_array_4[3] = char_array_3[2] & 0x3f;
+
+  for (int j = 0; j < count; j++)
+    ret += BASE64_CHARS[static_cast<uint8_t>(char_array_4[j])];
+}
+
+std::string base64_encode(const std::vector<uint8_t> &buf) { return base64_encode(buf.data(), buf.size()); }
+
+std::string base64_encode(const uint8_t *buf, size_t buf_len) {
+  std::string ret;
+  int i = 0;
+  char char_array_3[3];
+
+  while (buf_len--) {
+    char_array_3[i++] = *(buf++);
+    if (i == 3) {
+      base64_encode_triple(char_array_3, 4, ret);
+      i = 0;
+    }
+  }
+
+  if (i) {
+    for (int j = i; j < 3; j++)
+      char_array_3[j] = '\0';
+
+    base64_encode_triple(char_array_3, i + 1, ret);
+
+    while ((i++ < 3))
+      ret += '=';
+  }
+
+  return ret;
+}
+
+std::vector<uint8_t> base64_decode(const std::string &encoded_string) {
+  // Calculate maximum decoded size: every 4 base64 chars = 3 bytes
+  size_t max_len = ((encoded_string.size() + 3) / 4) * 3;
+  std::vector<uint8_t> ret(max_len);
+  size_t actual_len = base64_decode(encoded_string, ret.data(), max_len);
+  ret.resize(actual_len);
+  return ret;
+}
+
+// --- Hex/binary formatting helpers ---
+
+std::string format_mac_address_pretty(const uint8_t *mac) {
+  char buf[18];
+  format_mac_addr_upper(mac, buf);
+  return std::string(buf);
+}
+
+std::string format_hex(const uint8_t *data, size_t length) {
+  std::string ret;
+  ret.resize(length * 2);
+  format_hex_to(&ret[0], length * 2 + 1, data, length);
+  return ret;
+}
+
+std::string format_hex(const std::vector<uint8_t> &data) { return format_hex(data.data(), data.size()); }
+
+// Shared implementation for uint8_t and string hex pretty formatting
+static std::string format_hex_pretty_uint8(const uint8_t *data, size_t length, char separator, bool show_length) {
+  if (data == nullptr || length == 0)
+    return "";
+  std::string ret;
+  size_t hex_len = separator ? (length * 3 - 1) : (length * 2);
+  ret.resize(hex_len);
+  format_hex_pretty_to(&ret[0], hex_len + 1, data, length, separator);
+  if (show_length && length > 4)
+    return ret + " (" + std::to_string(length) + ")";
+  return ret;
+}
+
+std::string format_hex_pretty(const uint8_t *data, size_t length, char separator, bool show_length) {
+  return format_hex_pretty_uint8(data, length, separator, show_length);
+}
+std::string format_hex_pretty(const std::vector<uint8_t> &data, char separator, bool show_length) {
+  return format_hex_pretty(data.data(), data.size(), separator, show_length);
+}
+
+std::string format_hex_pretty(const uint16_t *data, size_t length, char separator, bool show_length) {
+  if (data == nullptr || length == 0)
+    return "";
+  std::string ret;
+  size_t hex_len = separator ? (length * 5 - 1) : (length * 4);
+  ret.resize(hex_len);
+  format_hex_pretty_to(&ret[0], hex_len + 1, data, length, separator);
+  if (show_length && length > 4)
+    return ret + " (" + std::to_string(length) + ")";
+  return ret;
+}
+std::string format_hex_pretty(const std::vector<uint16_t> &data, char separator, bool show_length) {
+  return format_hex_pretty(data.data(), data.size(), separator, show_length);
+}
+std::string format_hex_pretty(const std::string &data, char separator, bool show_length) {
+  return format_hex_pretty_uint8(reinterpret_cast<const uint8_t *>(data.data()), data.length(), separator, show_length);
+}
+
+std::string format_bin(const uint8_t *data, size_t length) {
+  std::string result;
+  result.resize(length * 8);
+  format_bin_to(&result[0], length * 8 + 1, data, length);
+  return result;
+}
+
+// --- MAC address helpers ---
+
+std::string get_mac_address() {
+  uint8_t mac[6];
+  get_mac_address_raw(mac);
+  char buf[13];
+  format_mac_addr_lower_no_sep(mac, buf);
+  return std::string(buf);
+}
+
+std::string get_mac_address_pretty() {
+  char buf[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
+  return std::string(get_mac_address_pretty_into_buffer(buf));
+}
+
+}  // namespace esphome
diff --git a/esphome/core/alloc_helpers.h b/esphome/core/alloc_helpers.h
new file mode 100644
index 00000000000..fe350886b76
--- /dev/null
+++ b/esphome/core/alloc_helpers.h
@@ -0,0 +1,128 @@
+#pragma once
+
+/// @file alloc_helpers.h
+/// @brief Heap-allocating helper functions.
+///
+/// These functions return std::string and allocate heap memory on every call.
+/// On long-running embedded devices, repeated heap allocations fragment memory
+/// over time, eventually causing crashes even with free memory available.
+///
+/// Prefer the stack-based alternatives documented on each function instead.
+/// New code should avoid using these functions.
+
+#include <cstdarg>
+#include <cstdint>
+#include <cstdio>
+#include <string>
+#include <vector>
+
+namespace esphome {
+
+// --- String helpers (allocating) ---
+
+/// Truncate a string to a specific length.
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+std::string str_truncate(const std::string &str, size_t length);
+
+/// Extract the part of the string until either the first occurrence of the specified character, or the end
+/// (requires str to be null-terminated).
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+std::string str_until(const char *str, char ch);
+/// Extract the part of the string until either the first occurrence of the specified character, or the end.
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+std::string str_until(const std::string &str, char ch);
+
+/// Convert the string to lower case.
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+std::string str_lower_case(const std::string &str);
+
+/// Convert the string to upper case.
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+std::string str_upper_case(const std::string &str);
+
+/// Convert the string to snake case (lowercase with underscores).
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+std::string str_snake_case(const std::string &str);
+
+/// Sanitizes the input string by removing all characters but alphanumerics, dashes and underscores.
+/// @warning Allocates heap memory. Use str_sanitize_to() with a stack buffer instead.
+std::string str_sanitize(const std::string &str);
+
+/// snprintf-like function returning std::string of maximum length \p len (excluding null terminator).
+/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
+std::string __attribute__((format(printf, 1, 3))) str_snprintf(const char *fmt, size_t len, ...);
+
+/// sprintf-like function returning std::string.
+/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
+std::string __attribute__((format(printf, 1, 2))) str_sprintf(const char *fmt, ...);
+
+// --- Hex/binary formatting helpers (allocating) ---
+
+/// Format the six-byte array \p mac into a MAC address string.
+/// @warning Allocates heap memory. Use format_mac_addr_upper() with a stack buffer instead.
+std::string format_mac_address_pretty(const uint8_t mac[6]);
+
+/// Format the byte array \p data of length \p len in lowercased hex.
+/// @warning Allocates heap memory. Use format_hex_to() with a stack buffer instead.
+std::string format_hex(const uint8_t *data, size_t length);
+
+/// Format the vector \p data in lowercased hex.
+/// @warning Allocates heap memory. Use format_hex_to() with a stack buffer instead.
+std::string format_hex(const std::vector<uint8_t> &data);
+
+/// Format a byte array in pretty-printed, human-readable hex format.
+/// @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
+std::string format_hex_pretty(const uint8_t *data, size_t length, char separator = '.', bool show_length = true);
+
+/// Format a 16-bit word array in pretty-printed, human-readable hex format.
+/// @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
+std::string format_hex_pretty(const uint16_t *data, size_t length, char separator = '.', bool show_length = true);
+
+/// Format a byte vector in pretty-printed, human-readable hex format.
+/// @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
+std::string format_hex_pretty(const std::vector<uint8_t> &data, char separator = '.', bool show_length = true);
+
+/// Format a 16-bit word vector in pretty-printed, human-readable hex format.
+/// @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
+std::string format_hex_pretty(const std::vector<uint16_t> &data, char separator = '.', bool show_length = true);
+
+/// Format a string's bytes in pretty-printed, human-readable hex format.
+/// @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
+std::string format_hex_pretty(const std::string &data, char separator = '.', bool show_length = true);
+
+/// Format the byte array \p data of length \p len in binary.
+/// @warning Allocates heap memory. Use format_bin_to() with a stack buffer instead.
+std::string format_bin(const uint8_t *data, size_t length);
+
+// --- Value formatting helpers (allocating) ---
+
+/// Format a float value with accuracy decimals to a string.
+/// @deprecated Allocates heap memory. Use value_accuracy_to_buf() instead. Removed in 2026.7.0.
+__attribute__((deprecated("Allocates heap memory. Use value_accuracy_to_buf() instead. Removed in 2026.7.0.")))
+std::string
+value_accuracy_to_string(float value, int8_t accuracy_decimals);
+
+// --- Base64 helpers (allocating) ---
+
+/// Encode a byte buffer to base64 string.
+/// @warning Allocates heap memory.
+std::string base64_encode(const uint8_t *buf, size_t buf_len);
+/// Encode a byte vector to base64 string.
+/// @warning Allocates heap memory.
+std::string base64_encode(const std::vector<uint8_t> &buf);
+
+/// Decode a base64 string to a byte vector.
+/// @warning Allocates heap memory. Use base64_decode(data, len, buf, buf_len) with a pre-allocated buffer instead.
+std::vector<uint8_t> base64_decode(const std::string &encoded_string);
+
+// --- MAC address helpers (allocating) ---
+
+/// Get the device MAC address as a string, in lowercase hex notation.
+/// @warning Allocates heap memory. Use get_mac_address_into_buffer() instead.
+std::string get_mac_address();
+
+/// Get the device MAC address as a string, in colon-separated uppercase hex notation.
+/// @warning Allocates heap memory. Use get_mac_address_pretty_into_buffer() instead.
+std::string get_mac_address_pretty();
+
+}  // namespace esphome
diff --git a/esphome/core/helpers.cpp b/esphome/core/helpers.cpp
index 34ecaf137f0..1d0efd01ce5 100644
--- a/esphome/core/helpers.cpp
+++ b/esphome/core/helpers.cpp
@@ -221,31 +221,7 @@ bool str_endswith_ignore_case(const char *str, size_t str_len, const char *suffi
   return strncasecmp(str + str_len - suffix_len, suffix, suffix_len) == 0;
 }
 
-std::string str_truncate(const std::string &str, size_t length) {
-  return str.length() > length ? str.substr(0, length) : str;
-}
-std::string str_until(const char *str, char ch) {
-  const char *pos = strchr(str, ch);
-  return pos == nullptr ? std::string(str) : std::string(str, pos - str);
-}
-std::string str_until(const std::string &str, char ch) { return str.substr(0, str.find(ch)); }
-// wrapper around std::transform to run safely on functions from the ctype.h header
-// see https://en.cppreference.com/w/cpp/string/byte/toupper#Notes
-template<int (*fn)(int)> std::string str_ctype_transform(const std::string &str) {
-  std::string result;
-  result.resize(str.length());
-  std::transform(str.begin(), str.end(), result.begin(), [](unsigned char ch) { return fn(ch); });
-  return result;
-}
-std::string str_lower_case(const std::string &str) { return str_ctype_transform<std::tolower>(str); }
-std::string str_upper_case(const std::string &str) { return str_ctype_transform<std::toupper>(str); }
-std::string str_snake_case(const std::string &str) {
-  std::string result = str;
-  for (char &c : result) {
-    c = to_snake_case_char(c);
-  }
-  return result;
-}
+// str_truncate, str_until, str_lower_case, str_upper_case, str_snake_case moved to alloc_helpers.cpp
 char *str_sanitize_to(char *buffer, size_t buffer_size, const char *str) {
   if (buffer_size == 0) {
     return buffer;
@@ -258,41 +234,7 @@ char *str_sanitize_to(char *buffer, size_t buffer_size, const char *str) {
   return buffer;
 }
 
-std::string str_sanitize(const std::string &str) {
-  std::string result;
-  result.resize(str.size());
-  str_sanitize_to(&result[0], str.size() + 1, str.c_str());
-  return result;
-}
-std::string str_snprintf(const char *fmt, size_t len, ...) {
-  std::string str;
-  va_list args;
-
-  str.resize(len);
-  va_start(args, len);
-  size_t out_length = vsnprintf(&str[0], len + 1, fmt, args);
-  va_end(args);
-
-  if (out_length < len)
-    str.resize(out_length);
-
-  return str;
-}
-std::string str_sprintf(const char *fmt, ...) {
-  std::string str;
-  va_list args;
-
-  va_start(args, fmt);
-  size_t length = vsnprintf(nullptr, 0, fmt, args);
-  va_end(args);
-
-  str.resize(length);
-  va_start(args, fmt);
-  vsnprintf(&str[0], length + 1, fmt, args);
-  va_end(args);
-
-  return str;
-}
+// str_sanitize, str_snprintf, str_sprintf moved to alloc_helpers.cpp
 
 // Maximum size for name with suffix: 120 (max friendly name) + 1 (separator) + 6 (MAC suffix) + 1 (null term)
 static constexpr size_t MAX_NAME_WITH_SUFFIX_SIZE = 128;
@@ -341,11 +283,7 @@ size_t parse_hex(const char *str, size_t length, uint8_t *data, size_t count) {
   return chars;
 }
 
-std::string format_mac_address_pretty(const uint8_t *mac) {
-  char buf[18];
-  format_mac_addr_upper(mac, buf);
-  return std::string(buf);
-}
+// format_mac_address_pretty moved to alloc_helpers.cpp
 
 // Internal helper for hex formatting - base is 'a' for lowercase or 'A' for uppercase.
 // When separator is set, it is written unconditionally after each byte and the last
@@ -398,13 +336,7 @@ char *format_hex_to(char *buffer, size_t buffer_size, const uint8_t *data, size_
   return format_hex_internal(buffer, buffer_size, data, length, 0, 'a');
 }
 
-std::string format_hex(const uint8_t *data, size_t length) {
-  std::string ret;
-  ret.resize(length * 2);
-  format_hex_to(&ret[0], length * 2 + 1, data, length);
-  return ret;
-}
-std::string format_hex(const std::vector<uint8_t> &data) { return format_hex(data.data(), data.size()); }
+// format_hex (std::string returning overloads) moved to alloc_helpers.cpp
 
 char *format_hex_pretty_to(char *buffer, size_t buffer_size, const uint8_t *data, size_t length, char separator) {
   return format_hex_internal(buffer, buffer_size, data, length, separator, 'A');
@@ -441,43 +373,7 @@ char *format_hex_pretty_to(char *buffer, size_t buffer_size, const uint16_t *dat
   return buffer;
 }
 
-// Shared implementation for uint8_t and string hex formatting
-static std::string format_hex_pretty_uint8(const uint8_t *data, size_t length, char separator, bool show_length) {
-  if (data == nullptr || length == 0)
-    return "";
-  std::string ret;
-  size_t hex_len = separator ? (length * 3 - 1) : (length * 2);
-  ret.resize(hex_len);
-  format_hex_pretty_to(&ret[0], hex_len + 1, data, length, separator);
-  if (show_length && length > 4)
-    return ret + " (" + std::to_string(length) + ")";
-  return ret;
-}
-
-std::string format_hex_pretty(const uint8_t *data, size_t length, char separator, bool show_length) {
-  return format_hex_pretty_uint8(data, length, separator, show_length);
-}
-std::string format_hex_pretty(const std::vector<uint8_t> &data, char separator, bool show_length) {
-  return format_hex_pretty(data.data(), data.size(), separator, show_length);
-}
-
-std::string format_hex_pretty(const uint16_t *data, size_t length, char separator, bool show_length) {
-  if (data == nullptr || length == 0)
-    return "";
-  std::string ret;
-  size_t hex_len = separator ? (length * 5 - 1) : (length * 4);
-  ret.resize(hex_len);
-  format_hex_pretty_to(&ret[0], hex_len + 1, data, length, separator);
-  if (show_length && length > 4)
-    return ret + " (" + std::to_string(length) + ")";
-  return ret;
-}
-std::string format_hex_pretty(const std::vector<uint16_t> &data, char separator, bool show_length) {
-  return format_hex_pretty(data.data(), data.size(), separator, show_length);
-}
-std::string format_hex_pretty(const std::string &data, char separator, bool show_length) {
-  return format_hex_pretty_uint8(reinterpret_cast<const uint8_t *>(data.data()), data.length(), separator, show_length);
-}
+// format_hex_pretty (all std::string returning overloads) moved to alloc_helpers.cpp
 
 char *format_bin_to(char *buffer, size_t buffer_size, const uint8_t *data, size_t length) {
   if (buffer_size == 0) {
@@ -500,12 +396,7 @@ char *format_bin_to(char *buffer, size_t buffer_size, const uint8_t *data, size_
   return buffer;
 }
 
-std::string format_bin(const uint8_t *data, size_t length) {
-  std::string result;
-  result.resize(length * 8);
-  format_bin_to(&result[0], length * 8 + 1, data, length);
-  return result;
-}
+// format_bin moved to alloc_helpers.cpp
 
 ParseOnOffState parse_on_off(const char *str, const char *on, const char *off) {
   if (on == nullptr && ESPHOME_strcasecmp_P(str, ESPHOME_PSTR("on")) == 0)
@@ -537,11 +428,7 @@ static inline void normalize_accuracy_decimals(float &value, int8_t &accuracy_de
   }
 }
 
-std::string value_accuracy_to_string(float value, int8_t accuracy_decimals) {
-  char buf[VALUE_ACCURACY_MAX_LEN];
-  value_accuracy_to_buf(buf, value, accuracy_decimals);
-  return std::string(buf);
-}
+// value_accuracy_to_string moved to alloc_helpers.cpp
 
 size_t value_accuracy_to_buf(std::span<char, VALUE_ACCURACY_MAX_LEN> buf, float value, int8_t accuracy_decimals) {
   normalize_accuracy_decimals(value, accuracy_decimals);
@@ -606,45 +493,7 @@ static inline uint8_t base64_find_char(char c) {
 // Check if character is valid base64 or base64url
 static inline bool is_base64(char c) { return (isalnum(c) || (c == '+') || (c == '/') || (c == '-') || (c == '_')); }
 
-std::string base64_encode(const std::vector<uint8_t> &buf) { return base64_encode(buf.data(), buf.size()); }
-
-// Encode 3 input bytes to 4 base64 characters, append 'count' to ret.
-static inline void base64_encode_triple(const char *char_array_3, int count, std::string &ret) {
-  char char_array_4[4];
-  char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
-  char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
-  char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
-  char_array_4[3] = char_array_3[2] & 0x3f;
-
-  for (int j = 0; j < count; j++)
-    ret += BASE64_CHARS[static_cast<uint8_t>(char_array_4[j])];
-}
-
-std::string base64_encode(const uint8_t *buf, size_t buf_len) {
-  std::string ret;
-  int i = 0;
-  char char_array_3[3];
-
-  while (buf_len--) {
-    char_array_3[i++] = *(buf++);
-    if (i == 3) {
-      base64_encode_triple(char_array_3, 4, ret);
-      i = 0;
-    }
-  }
-
-  if (i) {
-    for (int j = i; j < 3; j++)
-      char_array_3[j] = '\0';
-
-    base64_encode_triple(char_array_3, i + 1, ret);
-
-    while ((i++ < 3))
-      ret += '=';
-  }
-
-  return ret;
-}
+// base64_encode (both overloads) moved to alloc_helpers.cpp
 
 size_t base64_decode(const std::string &encoded_string, uint8_t *buf, size_t buf_len) {
   return base64_decode(reinterpret_cast<const uint8_t *>(encoded_string.data()), encoded_string.size(), buf, buf_len);
@@ -705,14 +554,7 @@ size_t base64_decode(const uint8_t *encoded_data, size_t encoded_len, uint8_t *b
   return out;
 }
 
-std::vector<uint8_t> base64_decode(const std::string &encoded_string) {
-  // Calculate maximum decoded size: every 4 base64 chars = 3 bytes
-  size_t max_len = ((encoded_string.size() + 3) / 4) * 3;
-  std::vector<uint8_t> ret(max_len);
-  size_t actual_len = base64_decode(encoded_string, ret.data(), max_len);
-  ret.resize(actual_len);
-  return ret;
-}
+// base64_decode (vector-returning overload) moved to alloc_helpers.cpp
 
 /// Decode base64/base64url string directly into vector of little-endian int32 values
 /// @param base64 Base64 or base64url encoded string (both +/ and -_ accepted)
@@ -851,18 +693,7 @@ void HighFrequencyLoopRequester::stop() {
   this->started_ = false;
 }
 
-std::string get_mac_address() {
-  uint8_t mac[6];
-  get_mac_address_raw(mac);
-  char buf[13];
-  format_mac_addr_lower_no_sep(mac, buf);
-  return std::string(buf);
-}
-
-std::string get_mac_address_pretty() {
-  char buf[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
-  return std::string(get_mac_address_pretty_into_buffer(buf));
-}
+// get_mac_address, get_mac_address_pretty moved to alloc_helpers.cpp
 
 void get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE> buf) {
   uint8_t mac[6];
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index 54bc32a5a58..bb164f5034f 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -21,6 +21,12 @@
 
 #include "esphome/core/optional.h"
 
+// Backward compatibility re-export of heap-allocating helpers.
+// These functions have moved to alloc_helpers.h. External components should
+// update their includes to use #include "esphome/core/alloc_helpers.h" directly.
+// This re-export will be removed in 2026.11.0.
+#include "esphome/core/alloc_helpers.h"
+
 #ifdef USE_ESP8266
 #include <Esp.h>
 #include <pgmspace.h>
@@ -979,27 +985,13 @@ inline bool str_endswith_ignore_case(const std::string &str, const char *suffix)
   return str_endswith_ignore_case(str.c_str(), str.size(), suffix, strlen(suffix));
 }
 
-/// Truncate a string to a specific length.
-/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
-std::string str_truncate(const std::string &str, size_t length);
+// str_truncate moved to alloc_helpers.h - remove this include before 2026.11.0
 
-/// Extract the part of the string until either the first occurrence of the specified character, or the end
-/// (requires str to be null-terminated).
-std::string str_until(const char *str, char ch);
-/// Extract the part of the string until either the first occurrence of the specified character, or the end.
-std::string str_until(const std::string &str, char ch);
-
-/// Convert the string to lower case.
-std::string str_lower_case(const std::string &str);
-/// Convert the string to upper case.
-/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
-std::string str_upper_case(const std::string &str);
+// str_until, str_lower_case, str_upper_case moved to alloc_helpers.h - remove this comment before 2026.11.0
 
 /// Convert a single char to snake_case: lowercase and space to underscore.
 constexpr char to_snake_case_char(char c) { return (c == ' ') ? '_' : (c >= 'A' && c <= 'Z') ? c + ('a' - 'A') : c; }
-/// Convert the string to snake case (lowercase with underscores).
-/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
-std::string str_snake_case(const std::string &str);
+// str_snake_case moved to alloc_helpers.h - remove this comment before 2026.11.0
 
 /// Sanitize a single char: keep alphanumerics, dashes, underscores; replace others with underscore.
 constexpr char to_sanitized_char(char c) {
@@ -1022,9 +1014,7 @@ template<size_t N> inline char *str_sanitize_to(char (&buffer)[N], const char *s
   return str_sanitize_to(buffer, N, str);
 }
 
-/// Sanitizes the input string by removing all characters but alphanumerics, dashes and underscores.
-/// @warning Allocates heap memory. Use str_sanitize_to() with a stack buffer instead.
-std::string str_sanitize(const std::string &str);
+// str_sanitize moved to alloc_helpers.h - remove this comment before 2026.11.0
 
 /// Calculate FNV-1 hash of a string while applying snake_case + sanitize transformations.
 /// This computes object_id hashes directly from names without creating an intermediate buffer.
@@ -1040,13 +1030,7 @@ inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
   return hash;
 }
 
-/// snprintf-like function returning std::string of maximum length \p len (excluding null terminator).
-/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
-std::string __attribute__((format(printf, 1, 3))) str_snprintf(const char *fmt, size_t len, ...);
-
-/// sprintf-like function returning std::string.
-/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
-std::string __attribute__((format(printf, 1, 2))) str_sprintf(const char *fmt, ...);
+// str_snprintf, str_sprintf moved to alloc_helpers.h - remove this comment before 2026.11.0
 
 #ifdef USE_ESP8266
 // ESP8266: Use vsnprintf_P to keep format strings in flash (PROGMEM)
@@ -1441,189 +1425,26 @@ inline void format_mac_addr_lower_no_sep(const uint8_t *mac, char *output) {
   format_hex_to(output, MAC_ADDRESS_BUFFER_SIZE, mac, MAC_ADDRESS_SIZE);
 }
 
-/// Format the six-byte array \p mac into a MAC address.
-/// @warning Allocates heap memory. Use format_mac_addr_upper() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
-std::string format_mac_address_pretty(const uint8_t mac[6]);
-/// Format the byte array \p data of length \p len in lowercased hex.
-/// @warning Allocates heap memory. Use format_hex_to() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
-std::string format_hex(const uint8_t *data, size_t length);
-/// Format the vector \p data in lowercased hex.
-/// @warning Allocates heap memory. Use format_hex_to() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
-std::string format_hex(const std::vector<uint8_t> &data);
+// format_mac_address_pretty, format_hex (all overloads) moved to alloc_helpers.h
+// Remove this comment and the template overloads below before 2026.11.0
+
 /// Format an unsigned integer in lowercased hex, starting with the most significant byte.
 /// @warning Allocates heap memory. Use format_hex_to() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
 template<typename T, enable_if_t<std::is_unsigned<T>::value, int> = 0> std::string format_hex(T val) {
   val = convert_big_endian(val);
   return format_hex(reinterpret_cast<uint8_t *>(&val), sizeof(T));
 }
 /// Format the std::array \p data in lowercased hex.
 /// @warning Allocates heap memory. Use format_hex_to() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
 template<std::size_t N> std::string format_hex(const std::array<uint8_t, N> &data) {
   return format_hex(data.data(), data.size());
 }
 
-/** Format a byte array in pretty-printed, human-readable hex format.
- *
- * Converts binary data to a hexadecimal string representation with customizable formatting.
- * Each byte is displayed as a two-digit uppercase hex value, separated by the specified separator.
- * Optionally includes the total byte count in parentheses at the end.
- *
- * @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
- * Causes heap fragmentation on long-running devices.
- *
- * @param data Pointer to the byte array to format.
- * @param length Number of bytes in the array.
- * @param separator Character to use between hex bytes (default: '.').
- * @param show_length Whether to append the byte count in parentheses (default: true).
- * @return Formatted hex string, e.g., "A1.B2.C3.D4.E5 (5)" or "A1:B2:C3" depending on parameters.
- *
- * @note Returns empty string if data is nullptr or length is 0.
- * @note The length will only be appended if show_length is true AND the length is greater than 4.
- *
- * Example:
- * @code
- * uint8_t data[] = {0xA1, 0xB2, 0xC3};
- * format_hex_pretty(data, 3);           // Returns "A1.B2.C3" (no length shown for <= 4 parts)
- * uint8_t data2[] = {0xA1, 0xB2, 0xC3, 0xD4, 0xE5};
- * format_hex_pretty(data2, 5);          // Returns "A1.B2.C3.D4.E5 (5)"
- * format_hex_pretty(data2, 5, ':');     // Returns "A1:B2:C3:D4:E5 (5)"
- * format_hex_pretty(data2, 5, '.', false); // Returns "A1.B2.C3.D4.E5"
- * @endcode
- */
-std::string format_hex_pretty(const uint8_t *data, size_t length, char separator = '.', bool show_length = true);
+// format_hex_pretty (all overloads) moved to alloc_helpers.h
+// Remove this comment and the template overload below before 2026.11.0
 
-/** Format a 16-bit word array in pretty-printed, human-readable hex format.
- *
- * Similar to the byte array version, but formats 16-bit words as 4-digit hex values.
- *
- * @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
- * Causes heap fragmentation on long-running devices.
- *
- * @param data Pointer to the 16-bit word array to format.
- * @param length Number of 16-bit words in the array.
- * @param separator Character to use between hex words (default: '.').
- * @param show_length Whether to append the word count in parentheses (default: true).
- * @return Formatted hex string with 4-digit hex values per word.
- *
- * @note The length will only be appended if show_length is true AND the length is greater than 4.
- *
- * Example:
- * @code
- * uint16_t data[] = {0xA1B2, 0xC3D4};
- * format_hex_pretty(data, 2); // Returns "A1B2.C3D4" (no length shown for <= 4 parts)
- * uint16_t data2[] = {0xA1B2, 0xC3D4, 0xE5F6};
- * format_hex_pretty(data2, 3); // Returns "A1B2.C3D4.E5F6 (3)"
- * @endcode
- */
-std::string format_hex_pretty(const uint16_t *data, size_t length, char separator = '.', bool show_length = true);
-
-/** Format a byte vector in pretty-printed, human-readable hex format.
- *
- * Convenience overload for std::vector<uint8_t>. Formats each byte as a two-digit
- * uppercase hex value with customizable separator.
- *
- * @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
- * Causes heap fragmentation on long-running devices.
- *
- * @param data Vector of bytes to format.
- * @param separator Character to use between hex bytes (default: '.').
- * @param show_length Whether to append the byte count in parentheses (default: true).
- * @return Formatted hex string representation of the vector contents.
- *
- * @note The length will only be appended if show_length is true AND the vector size is greater than 4.
- *
- * Example:
- * @code
- * std::vector<uint8_t> data = {0xDE, 0xAD, 0xBE, 0xEF};
- * format_hex_pretty(data);        // Returns "DE.AD.BE.EF" (no length shown for <= 4 parts)
- * std::vector<uint8_t> data2 = {0xDE, 0xAD, 0xBE, 0xEF, 0xCA};
- * format_hex_pretty(data2);       // Returns "DE.AD.BE.EF.CA (5)"
- * format_hex_pretty(data2, '-');  // Returns "DE-AD-BE-EF-CA (5)"
- * @endcode
- */
-std::string format_hex_pretty(const std::vector<uint8_t> &data, char separator = '.', bool show_length = true);
-
-/** Format a 16-bit word vector in pretty-printed, human-readable hex format.
- *
- * Convenience overload for std::vector<uint16_t>. Each 16-bit word is formatted
- * as a 4-digit uppercase hex value in big-endian order.
- *
- * @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
- * Causes heap fragmentation on long-running devices.
- *
- * @param data Vector of 16-bit words to format.
- * @param separator Character to use between hex words (default: '.').
- * @param show_length Whether to append the word count in parentheses (default: true).
- * @return Formatted hex string representation of the vector contents.
- *
- * @note The length will only be appended if show_length is true AND the vector size is greater than 4.
- *
- * Example:
- * @code
- * std::vector<uint16_t> data = {0x1234, 0x5678};
- * format_hex_pretty(data); // Returns "1234.5678" (no length shown for <= 4 parts)
- * std::vector<uint16_t> data2 = {0x1234, 0x5678, 0x9ABC};
- * format_hex_pretty(data2); // Returns "1234.5678.9ABC (3)"
- * @endcode
- */
-std::string format_hex_pretty(const std::vector<uint16_t> &data, char separator = '.', bool show_length = true);
-
-/** Format a string's bytes in pretty-printed, human-readable hex format.
- *
- * Treats each character in the string as a byte and formats it in hex.
- * Useful for debugging binary data stored in std::string containers.
- *
- * @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
- * Causes heap fragmentation on long-running devices.
- *
- * @param data String whose bytes should be formatted as hex.
- * @param separator Character to use between hex bytes (default: '.').
- * @param show_length Whether to append the byte count in parentheses (default: true).
- * @return Formatted hex string representation of the string's byte contents.
- *
- * @note The length will only be appended if show_length is true AND the string length is greater than 4.
- *
- * Example:
- * @code
- * std::string data = "ABC";  // ASCII: 0x41, 0x42, 0x43
- * format_hex_pretty(data);   // Returns "41.42.43" (no length shown for <= 4 parts)
- * std::string data2 = "ABCDE";
- * format_hex_pretty(data2);  // Returns "41.42.43.44.45 (5)"
- * @endcode
- */
-std::string format_hex_pretty(const std::string &data, char separator = '.', bool show_length = true);
-
-/** Format an unsigned integer in pretty-printed, human-readable hex format.
- *
- * Converts the integer to big-endian byte order and formats each byte as hex.
- * The most significant byte appears first in the output string.
- *
- * @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
- * Causes heap fragmentation on long-running devices.
- *
- * @tparam T Unsigned integer type (uint8_t, uint16_t, uint32_t, uint64_t, etc.).
- * @param val The unsigned integer value to format.
- * @param separator Character to use between hex bytes (default: '.').
- * @param show_length Whether to append the byte count in parentheses (default: true).
- * @return Formatted hex string with most significant byte first.
- *
- * @note The length will only be appended if show_length is true AND sizeof(T) is greater than 4.
- *
- * Example:
- * @code
- * uint32_t value = 0x12345678;
- * format_hex_pretty(value);        // Returns "12.34.56.78" (no length shown for <= 4 parts)
- * uint64_t value2 = 0x123456789ABCDEF0;
- * format_hex_pretty(value2);       // Returns "12.34.56.78.9A.BC.DE.F0 (8)"
- * format_hex_pretty(value2, ':');  // Returns "12:34:56:78:9A:BC:DE:F0 (8)"
- * format_hex_pretty<uint16_t>(0x1234); // Returns "12.34"
- * @endcode
- */
+/// Format an unsigned integer in pretty-printed, human-readable hex format.
+/// @warning Allocates heap memory. Use format_hex_pretty_to() with a stack buffer instead.
 template<typename T, enable_if_t<std::is_unsigned<T>::value, int> = 0>
 std::string format_hex_pretty(T val, char separator = '.', bool show_length = true) {
   val = convert_big_endian(val);
@@ -1683,13 +1504,10 @@ inline char *format_bin_to(char (&buffer)[N], T val) {
   return format_bin_to(buffer, reinterpret_cast<const uint8_t *>(&val), sizeof(T));
 }
 
-/// Format the byte array \p data of length \p len in binary.
-/// @warning Allocates heap memory. Use format_bin_to() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
-std::string format_bin(const uint8_t *data, size_t length);
+// format_bin moved to alloc_helpers.h - remove this comment and template overload before 2026.11.0
+
 /// Format an unsigned integer in binary, starting with the most significant byte.
 /// @warning Allocates heap memory. Use format_bin_to() with a stack buffer instead.
-/// Causes heap fragmentation on long-running devices.
 template<typename T, enable_if_t<std::is_unsigned<T>::value, int> = 0> std::string format_bin(T val) {
   val = convert_big_endian(val);
   return format_bin(reinterpret_cast<uint8_t *>(&val), sizeof(T));
@@ -1705,9 +1523,7 @@ enum ParseOnOffState : uint8_t {
 /// Parse a string that contains either on, off or toggle.
 ParseOnOffState parse_on_off(const char *str, const char *on = nullptr, const char *off = nullptr);
 
-/// @deprecated Allocates heap memory. Use value_accuracy_to_buf() instead. Removed in 2026.7.0.
-ESPDEPRECATED("Allocates heap memory. Use value_accuracy_to_buf() instead. Removed in 2026.7.0.", "2026.1.0")
-std::string value_accuracy_to_string(float value, int8_t accuracy_decimals);
+// value_accuracy_to_string moved to alloc_helpers.h - remove this comment before 2026.11.0
 
 /// Maximum buffer size for value_accuracy formatting (float ~15 chars + space + UOM ~40 chars + null)
 static constexpr size_t VALUE_ACCURACY_MAX_LEN = 64;
@@ -1721,10 +1537,8 @@ size_t value_accuracy_with_uom_to_buf(std::span<char, VALUE_ACCURACY_MAX_LEN> bu
 /// Derive accuracy in decimals from an increment step.
 int8_t step_to_accuracy_decimals(float step);
 
-std::string base64_encode(const uint8_t *buf, size_t buf_len);
-std::string base64_encode(const std::vector<uint8_t> &buf);
-
-std::vector<uint8_t> base64_decode(const std::string &encoded_string);
+// base64_encode (both overloads), base64_decode (vector overload) moved to alloc_helpers.h
+// Remove this comment before 2026.11.0
 size_t base64_decode(std::string const &encoded_string, uint8_t *buf, size_t buf_len);
 size_t base64_decode(const uint8_t *encoded_data, size_t encoded_len, uint8_t *buf, size_t buf_len);
 
@@ -2160,15 +1974,7 @@ class HighFrequencyLoopRequester {
 /// Get the device MAC address as raw bytes, written into the provided byte array (6 bytes).
 void get_mac_address_raw(uint8_t *mac);  // NOLINT(readability-non-const-parameter)
 
-/// Get the device MAC address as a string, in lowercase hex notation.
-/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
-/// Use get_mac_address_into_buffer() instead.
-std::string get_mac_address();
-
-/// Get the device MAC address as a string, in colon-separated uppercase hex notation.
-/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
-/// Use get_mac_address_pretty_into_buffer() instead.
-std::string get_mac_address_pretty();
+// get_mac_address, get_mac_address_pretty moved to alloc_helpers.h - remove this comment before 2026.11.0
 
 /// Get the device MAC address into the given buffer, in lowercase hex notation.
 /// Assumes buffer length is MAC_ADDRESS_BUFFER_SIZE (12 digits for hexadecimal representation followed by null
diff --git a/script/ci-custom.py b/script/ci-custom.py
index 6dce86924e0..02ec08bc318 100755
--- a/script/ci-custom.py
+++ b/script/ci-custom.py
@@ -722,18 +722,22 @@ def lint_trailing_whitespace(fname, match):
 # Heap-allocating helpers that cause fragmentation on long-running embedded devices.
 # These return std::string and should be replaced with stack-based alternatives.
 HEAP_ALLOCATING_HELPERS = {
+    "base64_encode": "base64_encode_to() with a pre-allocated buffer",
     "format_bin": "format_bin_to() with a stack buffer",
     "format_hex": "format_hex_to() with a stack buffer",
     "format_hex_pretty": "format_hex_pretty_to() with a stack buffer",
     "format_mac_address_pretty": "format_mac_addr_upper() with a stack buffer",
     "get_mac_address": "get_mac_address_into_buffer() with a stack buffer",
     "get_mac_address_pretty": "get_mac_address_pretty_into_buffer() with a stack buffer",
+    "str_lower_case": "manual tolower() with a stack buffer",
     "str_sanitize": "str_sanitize_to() with a stack buffer",
     "str_truncate": "removal (function is unused)",
+    "str_until": "manual strchr()/find() with a StringRef or stack buffer",
     "str_upper_case": "removal (function is unused)",
     "str_snake_case": "removal (function is unused)",
     "str_sprintf": "snprintf() with a stack buffer",
     "str_snprintf": "snprintf() with a stack buffer",
+    "value_accuracy_to_string": "value_accuracy_to_buf() with a stack buffer",
 }
 
 
@@ -743,24 +747,33 @@ HEAP_ALLOCATING_HELPERS = {
     # get_mac_address(?!_) ensures we don't match get_mac_address_into_buffer, etc.
     # CPP_RE_EOL captures rest of line so NOLINT comments are detected
     r"[^\w]("
+    r"base64_encode(?!_)|"
     r"format_bin(?!_)|"
     r"format_hex(?!_)|"
     r"format_hex_pretty(?!_)|"
     r"format_mac_address_pretty|"
     r"get_mac_address_pretty(?!_)|"
     r"get_mac_address(?!_)|"
+    r"str_lower_case|"
     r"str_sanitize(?!_)|"
     r"str_truncate|"
+    r"str_until|"
     r"str_upper_case|"
     r"str_snake_case|"
     r"str_sprintf|"
-    r"str_snprintf"
+    r"str_snprintf|"
+    r"value_accuracy_to_string"
     r")\s*\(" + CPP_RE_EOL,
     include=cpp_include,
     exclude=[
         # The definitions themselves
+        "esphome/core/alloc_helpers.h",
+        "esphome/core/alloc_helpers.cpp",
+        # Backward compatibility re-exports (remove before 2026.11.0)
         "esphome/core/helpers.h",
         "esphome/core/helpers.cpp",
+        # Vendored third-party library
+        "esphome/components/http_request/httplib.h",
     ],
 )
 def lint_no_heap_allocating_helpers(fname, match):
@@ -812,6 +825,7 @@ def lint_no_sprintf(fname, match):
         "esphome/components/http_request/httplib.h",
         # Deprecated helpers that return std::string
         "esphome/core/helpers.cpp",
+        "esphome/core/alloc_helpers.cpp",
         # The using declaration itself
         "esphome/core/helpers.h",
         # Test fixtures - not production embedded code