If you encounter an issue please use the arduino ide to install boards and libraries until we update this thread about a fix.

The arduino web site is currently returning invalid json (php) that might be written to your downloaded board index files. The .index files can be deleted from here "c:\users\[yourname]\appData\local\arduino15"

Clicking the "Update" button in board manager will redownload the incorrect .index files. This applies to the library_index.json and the package_index.json files that are automatically downloaded from the arduino .cc web sites.

If you find that the arduino ide has the same issue you can unpack the attached zip (contains two .json files) into the "arduino15" folder mentioned below. Until the issue is resolved, after applying the files, do not reopen the arduino ide board manager it might cause the problem. Do not use the "Check for updates" in the visual micro board or library manager. (copy the .json files back if you do that by mistake)