jp is a command line tool that reformats JSON to make it easier to read:

$ cat names.json
{"names":["Paul","Amy"]}
$ jp names.json
{
  "names": [
    "Paul",
    "Amy"
  ]
}

It is insanely fast, doesn't mess with the data, and handles invalid JSON (within reason). For more information see the project homepage.

Using Homebrew:

brew install https://gist.github.com/paulhammond/9441506/raw/jp.rb

If you don't use Homebrew you can download a precompiled binary and copy the jp file inside to somewhere in your path.

Or if you have a working go installation run go get github.com/paulhammond/jp.