The STM32 Flash loader demonstrator (FLASHER-STM32) is a free software PC utility from STMicroelectronics, which runs on PC and communicates through the RS232 with the STM32 system memory bootloader.
To get an example of how to execute the device bootloader, refer to the STM32 microcontroller system memory boot mode Application note (AN2606).
To get information about the USART protocol used in the STM32 bootloader, refer to the USART protocol used in the STM32 bootloader Application note (AN3155).
Remember to put your STM32 in boot mode before to run Flash Loader.
For example for put in boot mode the STM32L031K6 is necessary connect to VCC (VDD) the boot pin that is pin 31.
Up to now, 10-November-2017, there is a problem to program the STM32L0x1/2/3 (32KFlash) using the standard Flash Loader (ver.2.8.0) present on the STM Internet site.
If you had the necessity to program the STM32L0x1/2/3 download this release (ver.2.9.0) of the Flash Loader and use it.