JsonHelper.cs

class JsonHelper
{
	public static string FormatJson(string str, string indentString = "\t")
	{
		var indent = 0;
		var quoted = false;
		var sb = new StringBuilder();
		for (var i = 0; i < str.Length; i++)
		{
			var ch = str[i];
			switch (ch)
			{
				case '{':
				case '[':
					sb.Append(ch);
					if (!quoted)
					{
						sb.AppendLine();
						foreach (var e in Enumerable.Range(0, ++indent))
							sb.Append(indentString);
					}
					break;
				case '}':
				case ']':
					if (!quoted)
					{
						sb.AppendLine();
						foreach (var e in Enumerable.Range(0, --indent))
							sb.Append(indentString);
					}
					sb.Append(ch);
					break;
				case '"':
					sb.Append(ch);
					bool escaped = false;
					var index = i;
					while (index > 0 && str[--index] == '\\')
						escaped = !escaped;
					if (!escaped)
						quoted = !quoted;
					break;
				case ',':
					sb.Append(ch);
					if (!quoted)
					{
						sb.AppendLine();
						foreach (var e in Enumerable.Range(0, indent))
							sb.Append(indentString);
					}
					break;
				case ':':
					sb.Append(ch);
					if (!quoted)
						sb.Append(" ");
					break;
				default:
					sb.Append(ch);
					break;
			}
		}
		return sb.ToString();
	}
}