JSON formatter in C#?

Question

You could also use the Newtonsoft.Json library for this and call SerializeObject with the Formatting.Indented enum -

var x = JsonConvert.SerializeObject(jsonString, Formatting.Indented);

Documentation: Serialize an Object

---

Update -

Just tried it again. Pretty sure this used to work - perhaps it changed in a subsequent version or perhaps i'm just imagining things. Anyway, as per the comments below, it doesn't quite work as expected. These do, however (just tested in linqpad). The first one is from the comments, the 2nd one is an example i found elsewhere in SO -

void Main()
{
    //Example 1
    var t = "{\"x\":57,\"y\":57.0,\"z\":\"Yes\"}";
    var obj = Newtonsoft.Json.JsonConvert.DeserializeObject(t); 
    var f = Newtonsoft.Json.JsonConvert.SerializeObject(obj, Newtonsoft.Json.Formatting.Indented);
    Console.WriteLine(f);

    //Example 2
    JToken jt = JToken.Parse(t);
    string formatted = jt.ToString(Newtonsoft.Json.Formatting.Indented);
    Console.WriteLine(formatted);

    //Example 2 in one line -
    Console.WriteLine(JToken.Parse(t).ToString(Newtonsoft.Json.Formatting.Indented));
}

I updated the old version, now it should support unquoted values such as integers and booleans.

I refactored the previous version and got the final version: The code is shorter and cleaner. Only require one extension method. The most important: fixed some bugs.

class JsonHelper
{
    private const string INDENT_STRING = "    ";
    public static string FormatJson(string str)
    {
        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();
                        Enumerable.Range(0, ++indent).ForEach(item => sb.Append(INDENT_STRING));
                    }
                    break;
                case '}':
                case ']':
                    if (!quoted)
                    {
                        sb.AppendLine();
                        Enumerable.Range(0, --indent).ForEach(item => sb.Append(INDENT_STRING));
                    }
                    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();
                        Enumerable.Range(0, indent).ForEach(item => sb.Append(INDENT_STRING));
                    }
                    break;
                case ':':
                    sb.Append(ch);
                    if (!quoted)
                        sb.Append(" ");
                    break;
                default:
                    sb.Append(ch);
                    break;
            }
        }
        return sb.ToString();
    }
}

static class Extensions
{
    public static void ForEach<T>(this IEnumerable<T> ie, Action<T> action)
    {
        foreach (var i in ie)
        {
            action(i);
        }
    }
}

Shorter sample for json.net library.

using Newtonsoft.Json;

private static string format_json(string json)
{
    dynamic parsedJson = JsonConvert.DeserializeObject(json);
    return JsonConvert.SerializeObject(parsedJson, Formatting.Indented);
}

PS: You can wrap the formatted json text with tag to print as it is on the html page.

This worked for me using System.Text.Json in .Net Core 3.1

 public string PrettyJson(string unPrettyJson)
 {
     var options = new JsonSerializerOptions(){
         WriteIndented = true
     };

     var jsonElement = JsonSerializer.Deserialize<JsonElement>(unPrettyJson);

     return JsonSerializer.Serialize(jsonElement, options);
 }

Here's a compact version of a JSON beautifier.

private const string INDENT_STRING = "    ";

static string FormatJson(string json) {

    int indentation = 0;
    int quoteCount = 0;
    var result = 
        from ch in json
        let quotes = ch == '"' ? quoteCount++ : quoteCount
        let lineBreak = ch == ',' && quotes % 2 == 0 ? ch + Environment.NewLine +  String.Concat(Enumerable.Repeat(INDENT_STRING, indentation)) : null
        let openChar = ch == '{' || ch == '[' ? ch + Environment.NewLine + String.Concat(Enumerable.Repeat(INDENT_STRING, ++indentation)) : ch.ToString()
        let closeChar = ch == '}' || ch == ']' ? Environment.NewLine + String.Concat(Enumerable.Repeat(INDENT_STRING, --indentation)) + ch : ch.ToString()
        select lineBreak == null    
                    ? openChar.Length > 1 
                        ? openChar 
                        : closeChar
                    : lineBreak;

    return String.Concat(result);
}

Outputs:

 {
    "status":"OK",
     "results":[
         {
            "types":[
                 "locality",
                 "political"
            ],
             "formatted_address":"New York, NY, USA",
             "address_components":[
                 {
                    "long_name":"New York",
                     "short_name":"New York",
                     "types":[
                         "locality",
                         "political"
                    ]
                },
                 {
                    "long_name":"New York",
                     "short_name":"New York",
                     "types":[
                         "administrative_area_level_2",
                         "political"
                    ]
                },
                 {
                    "long_name":"New York",
                     "short_name":"NY",
                     "types":[
                         "administrative_area_level_1",
                         "political"
                    ]
                },
                 {
                    "long_name":"United States",
                     "short_name":"US",
                     "types":[
                         "country",
                         "political"
                    ]
                }
            ],
             "geometry":{
                "location":{
                    "lat":40.7143528,
                     "lng":-74.0059731
                },
                 "location_type":"APPROXIMATE",
                 "viewport":{
                    "southwest":{
                        "lat":40.5788964,
                         "lng":-74.2620919
                    },
                     "northeast":{
                        "lat":40.8495342,
                         "lng":-73.7498543
                    }
                },
                 "bounds":{
                    "southwest":{
                        "lat":40.4773990,
                         "lng":-74.2590900
                    },
                     "northeast":{
                        "lat":40.9175770,
                         "lng":-73.7002720
                    }
                }
            }
        }
    ]
}

I was very impressed by compact JSON formatter by Vince Panuccio.
Here is an improved version I now use:

public static string FormatJson(string json, string indent = "  ")
{
    var indentation = 0;
    var quoteCount = 0;
    var escapeCount = 0;

    var result =
        from ch in json ?? string.Empty
        let escaped = (ch == '\\' ? escapeCount++ : escapeCount > 0 ? escapeCount-- : escapeCount) > 0
        let quotes = ch == '"' && !escaped ? quoteCount++ : quoteCount
        let unquoted = quotes % 2 == 0
        let colon = ch == ':' && unquoted ? ": " : null
        let nospace = char.IsWhiteSpace(ch) && unquoted ? string.Empty : null
        let lineBreak = ch == ',' && unquoted ? ch + Environment.NewLine + string.Concat(Enumerable.Repeat(indent, indentation)) : null
        let openChar = (ch == '{' || ch == '[') && unquoted ? ch + Environment.NewLine + string.Concat(Enumerable.Repeat(indent, ++indentation)) : ch.ToString()
        let closeChar = (ch == '}' || ch == ']') && unquoted ? Environment.NewLine + string.Concat(Enumerable.Repeat(indent, --indentation)) + ch : ch.ToString()
        select colon ?? nospace ?? lineBreak ?? (
            openChar.Length > 1 ? openChar : closeChar
        );

    return string.Concat(result);
}

It fixes the following issues:

1. Escape sequences inside strings
2. Missing spaces after colon
3. Extra spaces after commas (or elsewhere)
4. Square and curly braces inside strings
5. Doesn't fail on null input

Outputs:

{
  "status": "OK",
  "results": [
    {
      "types": [
        "locality",
        "political"
      ],
      "formatted_address": "New York, NY, USA",
      "address_components": [
        {
          "long_name": "New York",
          "short_name": "New York",
          "types": [
            "locality",
            "political"
          ]
        },
        {
          "long_name": "New York",
          "short_name": "New York",
          "types": [
            "administrative_area_level_2",
            "political"
          ]
        },
        {
          "long_name": "New York",
          "short_name": "NY",
          "types": [
            "administrative_area_level_1",
            "political"
          ]
        },
        {
          "long_name": "United States",
          "short_name": "US",
          "types": [
            "country",
            "political"
          ]
        }
      ],
      "geometry": {
        "location": {
          "lat": 40.7143528,
          "lng": -74.0059731
        },
        "location_type": "APPROXIMATE",
        "viewport": {
          "southwest": {
            "lat": 40.5788964,
            "lng": -74.2620919
          },
          "northeast": {
            "lat": 40.8495342,
            "lng": -73.7498543
          }
        },
        "bounds": {
          "southwest": {
            "lat": 40.4773990,
            "lng": -74.2590900
          },
          "northeast": {
            "lat": 40.9175770,
            "lng": -73.7002720
          }
        }
      }
    }
  ]
}