Not trying to bash your project here, but why would I use a website for that when I can do it programmatically from the command line, without sending you my data?
Get-Content foo.json | ConvertFrom-Json | Export-Csv foo.csv
Get-Content foo.json | ConvertFrom-Json | Export-Csv foo.csv
PS: I'm the creator of this tool. This tool is a client side app and makes use of browser's File API to read and parse files. Source code - https://github.com/palerdot/exceljson
Shameless plug, we're still in alpha, but this already works great with PowerShell 6 on Mac and Linux as well: https://github.com/powershell/powershell/releases
Plug aside, the service looks great for quick conversions when PS isn't available (especially on mobile). Nice job with it. :)