No, The tool works locally in your browser and no data is uploaded to the server.
You can unminify js code but it will not be same as the original code. Minification replaces function names and variables with meaningless names. Using above unminify functionality you can still read code easily.
Yes, you can unminify HTML code using this tool.
Yes, you can use this tools to beautify code. Code formatting or beautification is the same process.
You can unminify CSS code using this tool.
You can deminify JavaScript code using this tool. Deminify and unminify is the same process.
No, you cannot compress or minify any code. This tools supports only unminify functionality for JS, CSS and HTML.
Yes, you can do that. Just past your code, select javascript option and format code.