nix/doc/manual/rl-next/pretty-json.md

synopsis	issues	prs
Prettified JSON output on the terminal	12555	12652

Scripts are mostly unaffected because for those, stdout will be a file or a pipe, not a terminal, and for those, the old single-line behavior applies.

--json --pretty can be passed to enable it even if the output is not a terminal. If your script creates a pseudoterminal for Nix's stdout, you can pass --no-pretty to disable the new behavior.