diff --git a/README.md b/README.md
index 98fbb8b..7e26cf3 100644
--- a/README.md
+++ b/README.md
@@ -1,36 +1,97 @@
-# Config payloads generation for Home Assistant MQTT discovery
+# HaMqttConfigBuilderLite
 
-A tiny library that will let you generate config payloads for Home Assistant MQTT discovery. These payload ar JSON key/value pairs.
+A lightweight, zero-dependency JSON builder for Home Assistant MQTT Discovery payloads.
 
-This is intended to replace [plapointe6/HAMqttDevice](https://github.com/plapointe6/HAMqttDevice) in my future iot devices.
+**Features:**
 
+- No `ArduinoJson` or STL containers
+- Single pre-allocated buffer (`String`)
+- Very low RAM usage (no heap fragmentation)
+- Support for nested objects (device, availability, etc.)
+- Efficient reuse of the `device` block for multiple sensor entities
 
-## Exemple
+---
 
-```c++
-#include "Arduino.h"
+## 🔧 Basic Usage
+
+```cpp
 #include "HaMqttConfigBuilder.h"
 
-String generateConfig() {
-  return HaMqttConfigBuilder()
-    .add("~", "homeassistant/light/my_light")
-    .add("unique_id", "my_light")
-    .add("name", "My test light")
-    .add("stat_t", "~/state")
-    .add("cmd_t", "~/cmd")
-    .generatePayload();
-}
+HaMqttConfigBuilder cfg;
 
-void setup() {
-  Serial.begin(115200);
-  Serial.println(generateConfig());
-}
+// Step 1: Define the device block once
+cfg.beginDevice()
+   .add("name",  "Plant Sensor")
+   .add("model", "v1.0")
+   .add("sw",    "0.1")
+.endDevice();
 
-void loop() {
-}
+// Step 2: Add the first sensor
+cfg.add("name",         "Soil Moisture")
+   .add("state_topic",  "plant/sensor/soil")
+   .add("unit_of_meas", "%")
+   .add("device_class", "humidity");
+
+Serial.println(cfg.generate());
+
+// Step 3: Reuse device block, add a second sensor
+cfg.nextSensor();
+cfg.add("name",         "Plant Battery")
+   .add("state_topic",  "plant/sensor/batt")
+   .add("unit_of_meas", "%")
+   .add("device_class", "battery");
+
+Serial.println(cfg.generate());
 ```
 
-Output:
+---
+
+## 📦 Output Example
+
+```json
+{
+  "device": {
+    "name": "Plant Sensor",
+    "model": "v1.0",
+    "sw": "0.1"
+  },
+  "name": "Soil Moisture",
+  "state_topic": "plant/sensor/soil",
+  "unit_of_meas": "%",
+  "device_class": "humidity"
+}
 ```
-{"~":"homeassistant/light/my_light","unique_id":"my_light","name":"My test light","stat_t":"~/state","cmd_t":"~/cmd"}
+
+---
+
+## 🔍 Extract Field Value
+
+You can extract values from the generated JSON using `getString()`:
+
+```cpp
+String topic;
+if (cfg.getString("state_topic", topic)) {
+  Serial.println("Topic is: " + topic);
+}
 ```
+
+---
+
+## 🧠 Memory Efficiency
+
+- Internally uses a single `String` buffer
+- Nested objects supported up to configurable max depth (default 6)
+- Device block is cached via position pointer to avoid duplication
+
+---
+
+## 💡 Tip
+
+Use `cfg.clear()` if you want to start over completely and redefine the device block.
+
+---
+
+## License
+
+MIT
+
diff --git a/src/HaMqttConfigBuilder.h b/src/HaMqttConfigBuilder.h
index 0240c19..b106c0e 100644
--- a/src/HaMqttConfigBuilder.h
+++ b/src/HaMqttConfigBuilder.h
@@ -1,54 +1,187 @@
-#include "Arduino.h"
+#pragma once
+/**
+ * HaMqttConfigBuilder
+ * -----------------------------------------------------------------
+ * Ultra-small Home Assistant MQTT Discovery JSON Builder
+ *   • Header-only, no STL containers, no ArduinoJson
+ *   • Single preallocated string as buffer → minimal RAM usage
+ *   • Nested objects (Default maxDepth = 6)
+ *   • Integer, Float, Bool, String fields without temporary objects
+ *   • Simple top-level lookup via getString(key, result)
+ *   • **Device caching**: `beginDevice()` / `endDevice()` + `nextSensor()`
+ *     → Device block is retained, sensor part is overwritten
+ */
+
+#include <Arduino.h>
+#include <stdlib.h>   // dtostrf
 
-// An helper class to generate a json Key/Value config payload for Home Assistant
 class HaMqttConfigBuilder {
+public:
+  static constexpr uint8_t kStaticMaxDepth = 6;   ///< Compile-time depth limit
 
-private:
-  struct Elem {
-    String key;
-    String str;
-    double num;
-  };
-  std::vector<Elem> elements;
+  explicit HaMqttConfigBuilder(size_t reserveBytes = 256, uint8_t maxDepth = 4)
+      : maxDepth_(maxDepth > kStaticMaxDepth ? kStaticMaxDepth : maxDepth) {
+    payload_.reserve(reserveBytes);
+    payload_ = '{';
+    depth_   = 0;
+    memset(first_, 1, sizeof(first_));
+  }
 
-public:
-  // Add an element to the config paylaod
-  HaMqttConfigBuilder& add(const String& key, const String& str) {
-    elements.push_back({key, str, 0});
+  /** Clear everything (including device block). */
+  void clear() {
+    payload_.remove(0);
+    payload_ = '{';
+    depth_   = 0;
+    memset(first_, 1, sizeof(first_));
+    deviceSet_ = false;
+    deviceEndPos_ = 0;
+  }
+
+  /* ------------------ Append fields ------------------ */
+
+  HaMqttConfigBuilder &add(const char *key, const char *val) {
+    beginField(key);
+    payload_ += '"';
+    escapeAndAppend(val);
+    payload_ += '"';
+    return *this;
+  }
+  HaMqttConfigBuilder &add(const char *key, const String &val) { return add(key, val.c_str()); }
+
+  HaMqttConfigBuilder &add(const char *key, long val) {
+    beginField(key);
+    payload_.concat(val);
+    return *this;
+  }
+
+  HaMqttConfigBuilder &add(const char *key, float val, uint8_t decimals = 2) {
+    beginField(key);
+    char buf[32];
+    dtostrf(val, 0, decimals, buf);
+    payload_ += buf;
     return *this;
   }
-  HaMqttConfigBuilder& add(const String& key, const double num) {
-    elements.push_back({key, "", num});
+
+  HaMqttConfigBuilder &add(const char *key, bool val) {
+    beginField(key);
+    payload_ += (val ? F("true") : F("false"));
     return *this;
   }
 
-  // Clear all elements
-  void clear() { elements.clear(); };
+  /* -------------- Nested objects -------------- */
 
-  // Generate the json key/value payload for home assistant
-  String generatePayload() {
-    String str = "{";
+  HaMqttConfigBuilder &beginObject(const char *key) {
+    if (depth_ >= maxDepth_) return *this;
+    beginField(key);
+    payload_ += '{';
+    ++depth_;
+    first_[depth_] = true;
+    return *this;
+  }
 
-    for(Elem elem : elements) {
-      str.concat('"');
-      str.concat(elem.key);
-      str.concat("\":");
-      
-      if (elem.str.length() > 0) {
-        str.concat('"');
-        str.concat(elem.str);
-        str.concat('"');
-      } else {
-        str.concat(elem.num);
-      }
-      str.concat(',');
-    }
+  HaMqttConfigBuilder &endObject() {
+    if (depth_ == 0) return *this;
+    payload_ += '}';
+    --depth_;
+    return *this;
+  }
+
+  /* -------------- Device block shortcuts -------------- */
+
+  HaMqttConfigBuilder &beginDevice() {
+    // Device can only be created once per clear
+    if (deviceSet_) return *this;               // already set
+    beginObject("device");
+    return *this;
+  }
+
+  HaMqttConfigBuilder &endDevice() {
+    if (deviceSet_) return *this;               // already finished
+    endObject();                                // closes "device"
+    deviceSet_   = true;
+    deviceEndPos_ = payload_.length();          // remember position after '}'
+    first_[0]    = false;                       // root already has entry
+    return *this;
+  }
+
+  /**
+   * Removes the last appended sensor fields, but keeps the device block.
+   * Afterwards, new fields can be appended via add().
+   */
+  void nextSensor() {
+    if (!deviceSet_) return;                    // no device → nothing to do
+    // remove everything after deviceEndPos_ (including previous sensor fields)
+    payload_.remove(deviceEndPos_);
+    depth_ = 0;                                // back to root level
+    // root already has an entry (device), so not first
+    first_[0] = false;
+  }
+
+  /* ----------------- Generate JSON ----------------- */
+
+  String generate() const {
+    String out = payload_;
+    for (int8_t d = depth_; d >= 0; --d) out += '}';
+    return out;
+  }
+
+  /* ----------- Simple top-level lookup ----------- */
+
+  bool getString(const char *key, String &result) const {
+    String json = generate();
+    String needle = '"' + String(key) + '"';
+
+    int pos = json.indexOf(needle);
+    if (pos < 0) return false;
 
-    if (str.endsWith(","))
-      str.setCharAt(str.length()-1, '}');
-    else
-      str.concat('}');
+    pos = json.indexOf(':', pos + needle.length());
+    if (pos < 0) return false;
+    ++pos;
 
-    return str;
+    while (pos < (int)json.length() && isspace(json[(size_t)pos])) ++pos;
+    if (pos >= (int)json.length() || json[(size_t)pos] != '"') return false;
+    ++pos;
+
+    int end = pos;
+    while (end < (int)json.length() && (json[(size_t)end] != '"' || json[(size_t)end - 1] == '\\')) ++end;
+    if (end >= (int)json.length()) return false;
+
+    result = json.substring(pos, end);
+    return true;
+  }
+
+private:
+  String        payload_;
+  uint8_t       depth_  = 0;
+  const uint8_t maxDepth_;
+  bool          first_[kStaticMaxDepth + 1];
+
+  bool   deviceSet_   = false;  ///< Device block has been finished
+  size_t deviceEndPos_ = 0;     ///< Index after '}' of device object
+
+  /* ----------- Internal helper for key entry ----------- */
+  inline void beginField(const char *key) {
+    if (!first_[depth_]) payload_ += ',';
+    else                 first_[depth_] = false;
+
+    payload_ += '"';
+    escapeAndAppend(key);
+    payload_ += "\":\"";
+  }
+
+  /* ---------------- JSON escaping ---------------- */
+  void escapeAndAppend(const char *s) {
+    for (; *s; ++s) {
+      switch (*s) {
+      case '"': payload_ += F("\\\""); break;
+      case '\\': payload_ += F("\\\\"); break;
+      case '\b': payload_ += F("\\b");  break;
+      case '\f': payload_ += F("\\f");  break;
+      case '\n': payload_ += F("\\n");  break;
+      case '\r': payload_ += F("\\r");  break;
+      case '\t': payload_ += F("\\t");  break;
+      default:   payload_ += *s;            break;
+      }
+    }
   }
-};
\ No newline at end of file
+};