Skip the online JSON formatters! Run this directly in the vim command line:
:!python -m json.tool
This is very handy when downloading or working with minified JSON and works in your current buffer.
To make it even easier, I set up a shortcut in my
vimrc which will run the above command but also set the filetype to
nnoremap ,j :set ft=json<cr>:%!python -m json.tool<cr>gg=G<cr>
Note my map leader is
, (comma), so
,j (for JSON) will call the function on my current buffer.