The simplest way is to use NodeJS. It takes a little code, but it's pretty simple. The code is listed below.

#!/usr/bin/env node

process.stdin.setEncoding('utf8');

var s = '';
process.stdin.on('readable', function() {
  var chunk = process.stdin.read();
  if (chunk !== null) {
    s += chunk;
  }
});

process.stdin.on('end', function() {
  try {
    process.stdout.write(JSON.stringify(JSON.parse(s), null, '  '));
  } catch(e) {
    process.stderr.write("Malformed JSON. Aborting.\n");
  }
});

Here's an example of how to use it:

$ echo '{"array":[1,2,3],"attrib":"value"}' | ppjson
{
  "array": [
    1,
    2,
    3
  ],
  "attrib": "value"
}