Pretty print JSON online with spaces or real tabs

Match whatever the file you are pasting into already uses. If a repo has an .editorconfig or a Prettier config, that is the answer. If you have no constraint, two spaces is the most common choice for JSON.

Yes, a real U+0009 character per indent level, not a run of spaces. You can confirm it after pasting by turning on whitespace rendering in your editor.

Marginally, and only because the file is larger. For anything you ship over a network, minify it; the readable version is for humans and version control.

It did not change value, only how it is written. JSON has one number type, so 1.50 and 1.5 are the same number and the serialiser prints the shorter form. If the exact digits matter, such as for currency, store the value as a string.

Not as one document. JSON Lines holds one independent JSON value per line, which is not valid JSON overall. Paste a single line at a time.