diff --git a/Sensor-API.md b/Sensor-API.md
index b3236989..99029dee 100644
--- a/Sensor-API.md
+++ b/Sensor-API.md
@@ -134,7 +134,21 @@ It should be wrapped in `#ifdef USE_WEBSERVER ... #endif  // USE_WEBSERVER`
 This callback ID is called to allow a sensor to prepare for saving configuration changes. To be used to save volatile data just before a restart.
 
 ### FUNC_COMMAND
-This callback ID is called when a sensor specific command ``Sensor\<xx\>`` is executed where xx is the sensor index.
+This callback ID is called when a sensor specific command ``Sensor<xx>`` is executed where xx is the sensor index.
+```
+// Data struct of FUNC_COMMAND ID
+struct XDRVMAILBOX {
+  uint16_t      valid;      // ???
+  uint16_t      index;      // Sensor index
+  uint16_t      data_len;   // Length of command string
+  uint16_t      payload16;  // ???
+  int16_t       payload;    // ???
+  uint8_t       grpflg;     // ???
+  uint8_t       notused;    // ???
+  char         *topic;      // Command topic
+  char         *data;       // Command string/value
+} XdrvMailbox;
+```
 
 ## Useful functions