GET /api/debug/heap/

FreeRTOS and lwIP heap state.

Auth: Bearer (powerUser).

---

Response 200

{
  "rtos": {
    "totalBytes": 30720,
    "freeBytes": 18240,
    "minEverFreeBytes": 12800,
    "largestFreeBlockBytes": 14336,
    "smallestFreeBlockBytes": 16,
    "freeBlockCount": 7,
    "allocCount": 1234,
    "freeCount": 1200
  },
  "lwip": {
    "totalBytes": 51200,
    "freeBytes": 38400,
    "minEverFreeBytes": 28000
  }
}

Response fields

Field	Type	Description
rtos.totalBytes	number	Total FreeRTOS heap size (configTOTAL_HEAP_SIZE)
rtos.freeBytes	number	Current free space (sum of all free blocks)
rtos.minEverFreeBytes	number	All-time minimum free space (watermark)
rtos.largestFreeBlockBytes	number	Size of the largest free block (fragmentation indicator)
rtos.smallestFreeBlockBytes	number	Size of the smallest free block
rtos.freeBlockCount	number	Number of free blocks
rtos.allocCount	number	Number of successful pvPortMalloc calls since startup
rtos.freeCount	number	Number of successful vPortFree calls since startup
lwip.totalBytes	number	Total lwIP heap size
lwip.freeBytes	number	Current free space in the lwIP heap
lwip.minEverFreeBytes	number	All-time minimum free space in the lwIP heap

When freeBytes > 0, the FreeRTOS heap fragmentation metric is 1 - largestFreeBlockBytes / freeBytes. If largestFreeBlockBytes is significantly smaller than freeBytes, a large allocation may fail despite sufficient total free memory. When freeBytes == 0, the Web UI reports 0% without evaluating the formula.