diff --git a/code/espurna/config/general.h b/code/espurna/config/general.h
index 3032f5d8..c00fad50 100644
--- a/code/espurna/config/general.h
+++ b/code/espurna/config/general.h
@@ -81,7 +81,7 @@
 #define MQTT_MESSAGE_EVENT      2
 
 // Custom get and set postfixes
-// Use something like "/status" or "/set", with trailing slash
+// Use something like "/status" or "/set", with leading slash
 #define MQTT_USE_GETTER         ""
 #define MQTT_USE_SETTER         ""
 
diff --git a/code/espurna/config/prototypes.h b/code/espurna/config/prototypes.h
index 6311efb3..2c4fe604 100644
--- a/code/espurna/config/prototypes.h
+++ b/code/espurna/config/prototypes.h
@@ -5,7 +5,7 @@
 #include <AsyncMqttClient.h>
 #include <functional>
 
-typedef std::function<char *(void)> apiGetCallbackFunction;
+typedef std::function<void(char *, size_t)> apiGetCallbackFunction;
 typedef std::function<void(const char *)> apiPutCallbackFunction;
 void apiRegister(const char * url, const char * key, apiGetCallbackFunction getFn, apiPutCallbackFunction putFn = NULL);
 void mqttRegister(void (*callback)(unsigned int, const char *, const char *));
diff --git a/code/espurna/dht.ino b/code/espurna/dht.ino
index 502bcbdb..61ba98f5 100644
--- a/code/espurna/dht.ino
+++ b/code/espurna/dht.ino
@@ -13,25 +13,29 @@ Copyright (C) 2016-2017 by Xose Pérez <xose dot perez at gmail dot com>
 
 DHT dht(DHT_PIN, DHT_TYPE, DHT_TIMING);
 
-char dhtTemperature[6];
-char dhtHumidity[6];
+double _dhtTemperature = 0;
+unsigned int _dhtHumidity = 0;
 
 // -----------------------------------------------------------------------------
 // Values
 // -----------------------------------------------------------------------------
 
-char * getDHTTemperature() {
-    return dhtTemperature;
+double getDHTTemperature() {
+    return _dhtTemperature;
 }
 
-char * getDHTHumidity() {
-    return dhtHumidity;
+unsigned int getDHTHumidity() {
+    return _dhtHumidity;
 }
 
 void dhtSetup() {
     dht.begin();
-    apiRegister("/api/temperature", "temperature", getDHTTemperature);
-    apiRegister("/api/humidity", "humidity", getDHTHumidity);
+    apiRegister("/api/temperature", "temperature", [](char * buffer, size_t len) {
+        dtostrf(_dhtTemperature, len-1, 1, buffer);
+    });
+    apiRegister("/api/humidity", "humidity", [](char * buffer, size_t len) {
+        snprintf(buffer, len, "%d", _dhtHumidity);
+    });
 }
 
 void dhtLoop() {
@@ -52,25 +56,30 @@ void dhtLoop() {
 
         } else {
 
-            dtostrf(t, 4, 1, dhtTemperature);
-            itoa((int) h, dhtHumidity, 10);
+            _dhtTemperature = t;
+            _dhtHumidity = h;
 
-            DEBUG_MSG("[DHT] Temperature: %s\n", dhtTemperature);
-            DEBUG_MSG("[DHT] Humidity: %s\n", dhtHumidity);
+            char temperature[6];
+            char humidity[6];
+            dtostrf(t, 4, 1, temperature);
+            itoa((unsigned int) h, humidity, 10);
+
+            DEBUG_MSG("[DHT] Temperature: %s\n", temperature);
+            DEBUG_MSG("[DHT] Humidity: %s\n", humidity);
 
             // Send MQTT messages
-            mqttSend(getSetting("dhtTmpTopic", DHT_TEMPERATURE_TOPIC).c_str(), dhtTemperature);
-            mqttSend(getSetting("dhtHumTopic", DHT_HUMIDITY_TOPIC).c_str(), dhtHumidity);
+            mqttSend(getSetting("dhtTmpTopic", DHT_TEMPERATURE_TOPIC).c_str(), temperature);
+            mqttSend(getSetting("dhtHumTopic", DHT_HUMIDITY_TOPIC).c_str(), humidity);
 
             // Send to Domoticz
             #if ENABLE_DOMOTICZ
-                domoticzSend("dczTmpIdx", dhtTemperature);
-                domoticzSend("dczHumIdx", dhtHumidity);
+                domoticzSend("dczTmpIdx", temperature);
+                domoticzSend("dczHumIdx", humidity);
             #endif
 
             // Update websocket clients
             char buffer[100];
-            sprintf_P(buffer, PSTR("{\"dhtVisible\": 1, \"dhtTmp\": %s, \"dhtHum\": %s}"), dhtTemperature, dhtHumidity);
+            sprintf_P(buffer, PSTR("{\"dhtVisible\": 1, \"dhtTmp\": %s, \"dhtHum\": %s}"), temperature, humidity);
             wsSend(buffer);
 
         }
diff --git a/code/espurna/ds18b20.ino b/code/espurna/ds18b20.ino
index b4fc6795..2011530f 100644
--- a/code/espurna/ds18b20.ino
+++ b/code/espurna/ds18b20.ino
@@ -14,19 +14,21 @@ Copyright (C) 2016-2017 by Xose Pérez <xose dot perez at gmail dot com>
 OneWire oneWire(DS_PIN);
 DallasTemperature ds18b20(&oneWire);
 
-char dsTemperature[6];
+double _dsTemperature = 0;
 
 // -----------------------------------------------------------------------------
 // DS18B20
 // -----------------------------------------------------------------------------
 
-char * getDSTemperature() {
-    return dsTemperature;
+double getDSTemperature() {
+    return _dsTemperature;
 }
 
 void dsSetup() {
     ds18b20.begin();
-    apiRegister("/api/temperature", "temperature", getDSTemperature);
+    apiRegister("/api/temperature", "temperature", [](char * buffer, size_t len) {
+        dtostrf(_dsTemperature, len-1, 1, buffer);
+    });
 }
 
 void dsLoop() {
@@ -49,21 +51,23 @@ void dsLoop() {
 
         } else {
 
-            dtostrf(t, 4, 1, dsTemperature);
+            _dsTemperature = t;
 
-            DEBUG_MSG("[DS18B20] Temperature: %s\n", dsTemperature);
+            char temperature[6];
+            dtostrf(t, 5, 1, temperature);
+            DEBUG_MSG("[DS18B20] Temperature: %s\n", temperature);
 
             // Send MQTT messages
-            mqttSend(getSetting("dsTmpTopic", DS_TEMPERATURE_TOPIC).c_str(), dsTemperature);
+            mqttSend(getSetting("dsTmpTopic", DS_TEMPERATURE_TOPIC).c_str(), temperature);
 
             // Send to Domoticz
             #if ENABLE_DOMOTICZ
-                domoticzSend("dczTmpIdx", dsTemperature);
+                domoticzSend("dczTmpIdx", temperature);
             #endif
 
             // Update websocket clients
             char buffer[100];
-            sprintf_P(buffer, PSTR("{\"dsVisible\": 1, \"dsTmp\": %s}"), dsTemperature);
+            sprintf_P(buffer, PSTR("{\"dsVisible\": 1, \"dsTmp\": %s}"), temperature);
             wsSend(buffer);
 
         }
diff --git a/code/espurna/emon.ino b/code/espurna/emon.ino
index b41c0345..c9abb550 100644
--- a/code/espurna/emon.ino
+++ b/code/espurna/emon.ino
@@ -11,8 +11,8 @@ Copyright (C) 2016-2017 by Xose Pérez <xose dot perez at gmail dot com>
 #include <EmonLiteESP.h>
 
 EmonLiteESP emon;
-double current;
-char power[8];
+double _current = 0;
+unsigned int _power = 0;
 
 // -----------------------------------------------------------------------------
 // EMON
@@ -22,12 +22,12 @@ void setCurrentRatio(float value) {
     emon.setCurrentRatio(value);
 }
 
-char * getPower() {
-    return power;
+unsigned int getPower() {
+    return _power;
 }
 
 double getCurrent() {
-    return current;
+    return _current;
 }
 
 unsigned int currentCallback() {
@@ -53,7 +53,9 @@ void powerMonitorSetup() {
     );
     emon.setPrecision(EMON_CURRENT_PRECISION);
 
-    apiRegister("/api/power", "power", getPower);
+    apiRegister("/api/power", "power", [](char * buffer, size_t len) {
+        snprintf(buffer, len, "%d", _power);
+    });
 
 }
 
@@ -77,41 +79,46 @@ void powerMonitorLoop() {
 
         // Safety check: do not read current if relay is OFF
         if (!relayStatus(0)) {
-            current = 0;
+            _current = 0;
         } else {
-            current = emon.getCurrent(EMON_SAMPLES);
-            current -= EMON_CURRENT_OFFSET;
-            if (current < 0) current = 0;
+            _current = emon.getCurrent(EMON_SAMPLES);
+            _current -= EMON_CURRENT_OFFSET;
+            if (_current < 0) _current = 0;
         }
 
         if (measurements == 0) {
-            max = min = current;
+            max = min = _current;
         } else {
-            if (current > max) max = current;
-            if (current < min) min = current;
+            if (_current > max) max = _current;
+            if (_current < min) min = _current;
         }
-        sum += current;
+        sum += _current;
         ++measurements;
 
         float mainsVoltage = getSetting("emonMains", EMON_MAINS_VOLTAGE).toFloat();
 
-        //DEBUG_MSG("[ENERGY] Power now: %dW\n", int(current * mainsVoltage));
+        //DEBUG_MSG("[ENERGY] Power now: %dW\n", int(_current * mainsVoltage));
 
         // Update websocket clients
         char text[20];
-        sprintf_P(text, PSTR("{\"emonPower\": %d}"), int(current * mainsVoltage));
+        sprintf_P(text, PSTR("{\"emonPower\": %d}"), int(_current * mainsVoltage));
         wsSend(text);
 
         // Send MQTT messages averaged every EMON_MEASUREMENTS
         if (measurements == EMON_MEASUREMENTS) {
-            double p = (sum - max - min) * mainsVoltage / (measurements - 2);
-            sprintf(power, "%d", int(p));
+
+            _power = (int) ((sum - max - min) * mainsVoltage / (measurements - 2));
+            sum = 0;
+            measurements = 0;
+
+            char power[6];
+            snprintf(power, "%d", 6, _power);
             mqttSend(getSetting("emonPowerTopic", EMON_POWER_TOPIC).c_str(), power);
             #if ENABLE_DOMOTICZ
                 domoticzSend("dczPowIdx", power);
             #endif
-            sum = 0;
-            measurements = 0;
+
+
         }
 
         next_measurement += EMON_INTERVAL;
diff --git a/code/espurna/pow.ino b/code/espurna/pow.ino
index 5196ee35..606adb2b 100644
--- a/code/espurna/pow.ino
+++ b/code/espurna/pow.ino
@@ -144,17 +144,14 @@ void powSetup() {
         powAttachInterrupts();
     #endif
 
-    apiRegister("/api/power", "power", []() {
-        sprintf(apibuffer, "%d", getActivePower());
-        return apibuffer;
+    apiRegister("/api/power", "power", [](char * buffer, size_t len) {
+        snprintf(buffer, len, "%d", getActivePower());
     });
-    apiRegister("/api/current", "current", []() {
-        dtostrf(getCurrent(), 5, 2, apibuffer);
-        return apibuffer;
+    apiRegister("/api/current", "current", [](char * buffer, size_t len) {
+        dtostrf(getCurrent(), len-1, 2, buffer);
     });
-    apiRegister("/api/voltage", "voltage", []() {
-        sprintf(apibuffer, "%d", getVoltage());
-        return apibuffer;
+    apiRegister("/api/voltage", "voltage", [](char * buffer, size_t len) {
+        snprintf(buffer, len, "%d", getVoltage());
     });
 
 }
diff --git a/code/espurna/relay.ino b/code/espurna/relay.ino
index d99c2b6b..a5c0e892 100644
--- a/code/espurna/relay.ino
+++ b/code/espurna/relay.ino
@@ -181,8 +181,8 @@ void relaySetupAPI() {
         sprintf(key, "relay%d", relayID);
 
         apiRegister(url, key,
-            [relayID]() {
-                return (char *) (relayStatus(relayID) ? "1" : "0");
+            [relayID](char * buffer, size_t len) {
+				snprintf(buffer, "%d", len, relayStatus(relayID) ? 1 : 0);
             },
             [relayID](const char * payload) {
                 unsigned int value = payload[0] - '0';
diff --git a/code/espurna/web.ino b/code/espurna/web.ino
index 5396275e..0c00e78f 100644
--- a/code/espurna/web.ino
+++ b/code/espurna/web.ino
@@ -535,14 +535,19 @@ ArRequestHandlerFunction _bindAPI(unsigned int apiID) {
             }
         }
 
-        char * value = strdup((api.getFn)());
+        char value[10];
+        (api.getFn)(value, 10);
+
+        // jump over leading spaces
+        char *p = value;
+        while ((unsigned char) *p == ' ') ++p;
 
         if (asJson) {
             char buffer[64];
-            sprintf_P(buffer, PSTR("{ \"%s\": %s }"), api.key, value);
+            sprintf_P(buffer, PSTR("{ \"%s\": %s }"), api.key, p);
             request->send(200, "application/json", buffer);
         } else {
-            request->send(200, "text/plain", value);
+            request->send(200, "text/plain", p);
         }
 
     };