Where Do I Put platform.local.txt?

The file platform.local.txt needs to be in the hardware folder that supports the board platform you are using. For example, to find the right folder for an ESP8266 board, follow these steps:

• Select a board from the ESP8266 list.
• Set preferences for a verbose compile,
  • From the Arduino IDE select Edit->File->Preferences.
  • Find the selection: "Show verbose output during: [] compilation [] upload"
  • Check the box for "compilation"
• Open a new sketch.
• Run Verify, (Sketch->Verify/Compile).
• Scroll up to the top of the Arduino IDE message area.
• Look for the text "Using core 'esp8266' from platform in folder" and make note of the path. This line will be near the top, before "Detecting libraries used...". This is the location you need to remember for saving platform.local.txt.

A sample of Arduino IDE message area text:

  C:\Program Files (x86)\Arduino\arduino-builder -dump-prefs ...
  C:\Program Files (x86)\Arduino\arduino-builder -compile -logger=machine ...
  Using board 'generic' from platform in folder: C:\Users\mhightower83\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.3.0
> Using core 'esp8266' from platform in folder: C:\Users\mhightower83\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.3.0
  Detecting libraries used...
  ...

For this sample, we would save the platform.local.txt file to:

C:\Users\mhightower83\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.3.0