Is there any tool to read/write EEPROM of STM32L from the host?
Yes there is a tool called STM32 ST-LINK utility. Using this one can view and edit the EEPROM memory contents. It can also used to program and erase the flash memory.I am using this for my STM32L151VBT6 MCU. Please note that it's used only for STM32 series MCUs but not used for other than STM32 like STM8 etc..

here is the downloadable link:http://www.st.com/web/en/catalog/tools/PF258168