JSON formatter in C

Question

Looking for a function that will take a string of Json as input and format it with line breaks and indentations  Validation would be a bonus  but isn t necessary  and I don t need to parse it into an object or anything   Anyone know of such a library     Sample input     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

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Even simpler one that I just wrote   public class JsonFormatter       public static string Indent                public static string PrettyPrint string input                var output   new StringBuilder input Length   2           char  quote   null          int depth   0           for int i 0  i lt input Length    i                        char ch   input i                switch  ch                                case                      case                          output Append ch                       if   quote HasValue                                                output AppendLine                            output Append Indent Repeat   depth                                              break                  case                      case                          if  quote HasValue                            output Append ch                       else                                               output AppendLine                            output Append Indent Repeat --depth                            output Append ch                                             break                  case                      case                           output Append ch                       if  quote HasValue                                                if   output IsEscaped i                               quote   null                                            else quote   ch                      break                  case                          output Append ch                       if   quote HasValue                                                output AppendLine                            output Append Indent Repeat depth                                              break                  case                          if  quote HasValue  output Append ch                       else output Append                             break                  default                      if  quote HasValue     char IsWhiteSpace ch                            output Append ch                       break                                   return output ToString              Necessary extensions       public static string Repeat this string str  int count                return new StringBuilder   Insert 0  str  count  ToString               public static bool IsEscaped this string str  int index                bool escaped   false          while  index  gt  0  amp  amp  str --index           escaped    escaped          return escaped             public static bool IsEscaped this StringBuilder str  int index                return str ToString   IsEscaped index           Sample output          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

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Just use JsonDocument and Utf8JsonWriter  No third-party library required  No target object for deserialization for jsonString required   using System IO  using System Text  using System Text Json      other code      public string Prettify string jsonString        using var stream   new MemoryStream        var document   JsonDocument Parse jsonString       var writer   new Utf8JsonWriter stream  new JsonWriterOptions   Indented   true         document WriteTo writer       writer Flush        return Encoding UTF8 GetString stream ToArray

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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         amp  amp  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  gt  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

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This version produces JSON that is more compact and in my opinion more readable since you can see more at one time   It does this by formatting the deepest layer inline or like a compact array structure   The code has no dependencies but is more complex         name   Seller       schema   dbo      CaptionFields    Caption   Id       fields           name   Id   type   Integer   length   10   autoincrement  true  nullable  false          name   FirstName   type   Text   length   50   autoincrement  false  nullable  false          name   LastName   type   Text   length   50   autoincrement  false  nullable  false          name   LotName   type   Text   length   50   autoincrement  false  nullable  true          name   LotDetailsURL   type   Text   length   255   autoincrement  false  nullable  true           The code follows  private class IndentJsonInfo       public IndentJsonInfo string prefix  char openingTag                Prefix   prefix          OpeningTag   openingTag          Data   new List lt string gt               public string Prefix      public char OpeningTag      public bool isOutputStarted      public List lt string gt  Data    internal static string IndentJSON string jsonString  int startIndent   0  int indentSpaces   2        if  String IsNullOrEmpty jsonString           return jsonString       try               var jsonCache   new List lt IndentJsonInfo gt             IndentJsonInfo currentItem   null           var sbResult   new StringBuilder             int curIndex   0          bool inQuotedText   false           var chunk   new StringBuilder             var saveChunk   new Action      gt                        if  chunk Length    0                  return              if  currentItem    null                  throw new Exception  Invalid JSON  No container                 currentItem Data Add chunk ToString                 chunk   new StringBuilder                         while  curIndex  lt  jsonString Length                        var cChar   jsonString curIndex               if  inQuotedText                                   Get the rest of quoted text                  chunk Append cChar                       Determine if the quote is escaped                  bool isEscaped   false                  var excapeIndex   curIndex                  while  excapeIndex  gt  0  amp  amp  jsonString --excapeIndex           isEscaped    isEscaped                   if  cChar         amp  amp   isEscaped                      inQuotedText   false                            else if  Char IsWhiteSpace cChar                                    Ignore all whitespace outside of quotes                            else                                  Outside of Quotes                  switch  cChar                                        case                              chunk Append cChar                           inQuotedText   true                          break                      case                              chunk Append cChar                           saveChunk                            break                      case                          case                              currentItem   new IndentJsonInfo chunk ToString    cChar                           jsonCache Add currentItem                           chunk   new StringBuilder                            break                      case                          case                              saveChunk                            for  int i   0  i  lt  jsonCache Count  i                                                          var item   jsonCache i                               var isLast   i    jsonCache Count - 1                              if   isLast                                                                if   item isOutputStarted                                                                        sbResult AppendLine                                             PadLeft  startIndent   i    indentSpaces                                            item Prefix   item OpeningTag                                       item isOutputStarted   true                                                                    var newIndentString      PadLeft  startIndent   i   1    indentSpaces                                   foreach  var listItem in item Data                                                                        sbResult AppendLine newIndentString   listItem                                                                     item Data   new List lt string gt                                                               else    If Last                                                               if                                          item OpeningTag         amp  amp  cChar                                                 item OpeningTag         amp  amp  cChar                                                                                                                     throw new Exception  Invalid JSON  Container Mismatch  Open      item OpeningTag       Close      cChar                                                                             string closing   null                                  if  item isOutputStarted                                                                        var newIndentString      PadLeft  startIndent   i   1    indentSpaces                                       foreach  var listItem in item Data                                                                                sbResult AppendLine newIndentString   listItem                                                                             closing   cChar ToString                                                                      else                                                                       closing                                           item Prefix   item OpeningTag                                           String Join     currentItem Data ToArray                                              cChar                                                                     jsonCache RemoveAt i                                   currentItem    jsonCache Count  gt  0    jsonCache jsonCache Count - 1    null                                  chunk Append closing                                                                                   break                      default                          chunk Append cChar                           break                                              curIndex                       if  inQuotedText              throw new Exception  Invalid JSON  Incomplete Quote            else if  jsonCache Count    0              throw new Exception  Invalid JSON  Incomplete Structure            else                       if  chunk Length  gt  0                  sbResult AppendLine    PadLeft startIndent   indentSpaces    chunk               var result   sbResult ToString                return result                      catch  Exception ex                throw      Comment out to return unformatted text if the format failed             Invalid JSON  skip the formatting          return jsonString            The function allows you to specify a starting point for the indentation because I use this as part of a process that assembles very large JSON formatted backup files

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All credits are to Frank Tzanabetis  However this is the shortest direct example  that also survives in case of empty string or broken original JSON string  using Newtonsoft Json  using Newtonsoft Json Linq               try               return JToken Parse jsonString  ToString Formatting Indented             catch               return jsonString

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J Bryan Price  a good example  but there are shortcomings     response    123  456     name     John        count   3      after formatting         response              123           456                          name     John                                     count    3                     improper bias

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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  gt  0   escapeCount--   escapeCount   gt  0         let quotes   ch         amp  amp   escaped   quoteCount     quoteCount         let unquoted   quotes   2    0         let colon   ch         amp  amp  unquoted          null         let nospace   char IsWhiteSpace ch   amp  amp  unquoted   string Empty   null         let lineBreak   ch         amp  amp  unquoted   ch   Environment NewLine   string Concat Enumerable Repeat indent  indentation     null         let openChar    ch           ch          amp  amp  unquoted   ch   Environment NewLine   string Concat Enumerable Repeat indent    indentation     ch ToString           let closeChar    ch           ch          amp  amp  unquoted   Environment NewLine   string Concat Enumerable Repeat indent  --indentation     ch   ch ToString           select colon    nospace    lineBreak                  openChar Length  gt  1   openChar   closeChar                 return string Concat result       It fixes the following issues    Escape sequences inside strings Missing spaces after colon Extra spaces after commas  or elsewhere  Square and curly braces inside strings 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

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This will put each item on a new line VB NET mytext   responseFromServer Replace  quot   quot   vbNewLine    quot   quot    C  mytext   responseFromServer Replace  quot   quot   Environment NewLine    quot   quot

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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  lt  str Length  i                          var ch   str i               switch  ch                                case                      case                          sb Append ch                       if   quoted                                                sb AppendLine                            Enumerable Range 0    indent  ForEach item   gt  sb Append INDENT STRING                                              break                  case                      case                          if   quoted                                                sb AppendLine                            Enumerable Range 0  --indent  ForEach item   gt  sb Append INDENT STRING                                              sb Append ch                       break                  case                          sb Append ch                       bool escaped   false                      var index   i                      while  index  gt  0  amp  amp  str --index                                   escaped    escaped                      if   escaped                          quoted    quoted                      break                  case                          sb Append ch                       if   quoted                                                sb AppendLine                            Enumerable Range 0  indent  ForEach item   gt  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 lt T gt  this IEnumerable lt T gt  ie  Action lt T gt  action                foreach  var i in ie                        action i

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As benjymous pointed out  you can use Newtonsoft Json with a temporary object and deserialize serialize   var obj   JsonConvert DeserializeObject jsonString    var formatted   JsonConvert SerializeObject obj  Formatting Indented

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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 lt JsonElement gt  unPrettyJson         return JsonSerializer Serialize jsonElement  options

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Fixed it    somewhat   public class JsonFormatter        region class members     const string Space            const int DefaultIndent   0      const string Indent   Space   Space   Space   Space      static readonly string NewLine   Environment NewLine       endregion      private enum JsonContextType               Object  Array            static void BuildIndents int indents  StringBuilder output                indents    DefaultIndent          for    indents  gt  0  indents--              output Append Indent               bool inDoubleString   false      bool inSingleString   false      bool inVariableAssignment   false      char prevChar     0        Stack lt JsonContextType gt  context   new Stack lt JsonContextType gt          bool InString                 return inDoubleString    inSingleString             public string PrettyPrint string input                var output   new StringBuilder input Length   2           char c           for  int i   0  i  lt  input Length  i                          c   input i                switch  c                                case                          if   InString                                                  if  inVariableAssignment     context Count  gt  0  amp  amp  context Peek      JsonContextType Array                                                         output Append NewLine                               BuildIndents context Count  output                                                     output Append c                           context Push JsonContextType Object                           output Append NewLine                           BuildIndents context Count  output                                             else                         output Append c                        break                   case                          if   InString                                                  output Append NewLine                           context Pop                            BuildIndents context Count  output                           output Append c                                             else                         output Append c                        break                   case                          output Append c                        if   InString                            context Push JsonContextType Array                        break                   case                          if   InString                                                  output Append c                           context Pop                                              else                         output Append c                        break                   case                          output Append c                       break                   case                          output Append c                        if   InString    amp  amp  context Peek      JsonContextType Array                                                BuildIndents context Count  output                           output Append NewLine                           BuildIndents context Count  output                           inVariableAssignment   false                                             break                   case                           if   inDoubleString  amp  amp  prevChar                                  inSingleString    inSingleString                       output Append c                       break                   case                          if   InString                                                  inVariableAssignment   true                          output Append Space                           output Append c                           output Append Space                                             else                         output Append c                        break                   case                          if   inSingleString  amp  amp  prevChar                                  inDoubleString    inDoubleString                       output Append c                       break                  case                          if  InString                            output Append c                       break                   default                      output Append c                       break                            prevChar   c                     return output ToString              credit  dead link

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The main reason of writing your own function is that JSON frameworks usually perform parsing of strings into  net types and converting them back to string  which may result in losing original strings  For example 0 0002 becomes 2E-4  I do not post my function  it s pretty same as other here  but here are the test cases  using System IO   using Newtonsoft Json   using NUnit Framework   namespace json formatter tests        TestFixture      internal class FormatterTests                Test          public void CompareWithNewtonsofJson                         string file   Path Combine TestContext CurrentContext TestDirectory   json    minified txt                 string json   File ReadAllText file                string newton   JsonPrettify json                  Double space are indent symbols which newtonsoft framework uses             string my   new Formatter       Format json                Assert AreEqual newton  my                       Test          public void EmptyArrayMustNotBeFormatted                         var input       na me                      var expected      r n t  na me       r n                 Assert AreEqual expected  new Formatter   Format input                        Test          public void EmptyObjectMustNotBeFormatted                         var input       na me                      var expected      r n t  na me       r n                 Assert AreEqual expected  new Formatter   Format input                        Test          public void MustAddLinebreakAfterBraces                         var input       name      value                  var expected      r n t  name      value   r n                 Assert AreEqual expected  new Formatter   Format input                        Test          public void MustFormatNestedObject                         var input       na me     val ue      name1       name2     value                   var expected      r n t  na me      val ue    r n t  name1      r n t t  name2      value   r n t  r n                 Assert AreEqual expected  new Formatter   Format input                        Test          public void MustHandleArray                         var input       name      value      name2      a      b      c                   var expected      r n t  name      value    r n t  name2      r n t t  a    r n t t  b    r n t t  c   r n t  r n                Assert AreEqual expected  new Formatter   Format input                        Test          public void MustHandleArrayOfObject                         var input       name      value      name2       na me     val ue        nam    e2     val        ue                    var expected                      r n t  name      value    r n t  name2      r n t t  r n t t t  na me      val ue   r n t t   r n t t  r n t t t  nam    e2      val        ue   r n t t  r n t  r n                Assert AreEqual expected  new Formatter   Format input                        Test          public void MustHandleEscapedString                         var input       na me     val ue      name1       nam    e2     val        ue                   var expected      r n t  na me      val ue    r n t  name1      r n t t  nam    e2      val        ue   r n t  r n                Assert AreEqual expected  new Formatter   Format input                        Test          public void MustIgnoreEscapedQuotesInsideString                         var input       na me          val ue                  var expected      r n t  na me          val ue   r n                 Assert AreEqual expected  new Formatter   Format input                        TestCase                TestCase                 TestCase                TestCase                TestCase                TestCase                TestCase                TestCase               public void MustIgnoreSpecialSymbolsInsideString string symbol                        string input       na    symbol    me      val    symbol    ue                  string expected      r n t  na    symbol    me      val    symbol    ue   r n                 Assert AreEqual expected  new Formatter   Format input                        Test          public void StringEndsWithEscapedBackslash                         var input       na me          val ue                  var expected      r n t  na me          val ue   r n                 Assert AreEqual expected  new Formatter   Format input                       private static string PrettifyUsingNewtosoft string json                        using  var stringReader   new StringReader json               using  var stringWriter   new StringWriter                                  var jsonReader   new JsonTextReader stringReader                   var jsonWriter   new JsonTextWriter stringWriter                                                                        Formatting   Formatting Indented                                                    jsonWriter WriteToken jsonReader                   return stringWriter ToString

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This is a variant of the accepted answer that I like to use  The commented parts result in what I consider a more readable format  you would need to comment out the adjacent code to see the difference    public class JsonHelper       private const int INDENT SIZE   4       public static string FormatJson string str                str    str        Replace                Replace                          var inserts   new List lt int   gt             bool quoted   false  escape   false          int depth   0  -1             for  int i   0  N   str Length  i  lt  N  i                          var chr   str i                if   escape  amp  amp   quoted                  switch  chr                                        case                          case                              inserts Add new     i   1  0  INDENT SIZE     depth                               int n    i    0          Contains str i - 1      0   -1                            inserts Add new     i  n  INDENT SIZE     depth   -n  INDENT SIZE - 1                             break                      case                              inserts Add new     i   1  0  INDENT SIZE   depth                               inserts Add new     i  -1  INDENT SIZE   depth  INDENT SIZE - 1                             break                      case                          case                              inserts Add new     i  -1  INDENT SIZE   --depth  0                               inserts Add new     i  -1  INDENT SIZE   depth--  0                             break                      case                              inserts Add new     i  0  1  1                             break                                 quoted    chr            quoted   quoted              escape    chr             escape   false                     if  inserts Count  gt  0                        var sb   new System Text StringBuilder str Length   2                int lastIndex   0              foreach  var insert in inserts                                int index   insert 0   before   insert 2   after   insert 3                   bool nlBefore    insert 1     -1   nlAfter    insert 1      1                    sb Append str Substring lastIndex  index - lastIndex                     if  nlBefore  sb AppendLine                    if  before  gt  0  sb Append new String      before                     sb Append str index                     if  nlAfter  sb AppendLine                    if  after  gt  0  sb Append new String      after                     lastIndex   index   1                             str   sb ToString                       return str Replace                Replace

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Example      public static string JsonFormatter string json                StringBuilder builder   new StringBuilder             bool quotes   false           bool ignore   false           int offset   0           int position   0           if  string IsNullOrEmpty json                         return string Empty                     json   json Replace Environment NewLine      Replace   t                 foreach  char character in json                        switch  character                                case                          if   ignore                                                quotes    quotes                                            break                  case                           if  quotes                                                ignore    ignore                                            break                             if  quotes                                builder Append character                             else                               switch  character                                        case                          case                              builder Append character                           builder Append Environment NewLine                           builder Append new string        offset   4                            break                      case                          case                              builder Append Environment NewLine                           builder Append new string      --offset   4                            builder Append character                           break                      case                              builder Append character                           builder Append Environment NewLine                           builder Append new string      offset   4                            break                      case                              builder Append character                           builder Append                               break                      default                          if  character                                                               builder Append character                                                     break                                     position                                     return builder ToString   Trim

User · Answer

You need to skip  r and  n in PrettyPrint    The output looks funny of there are some crlf s already present  or the source was already formatted

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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

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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

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There are already a bunch of great answers here that use Newtonsoft JSON  but here s one more that uses JObject Parse in combination with ToString    since that hasn t been mentioned yet   var jObj   Newtonsoft Json Linq JObject Parse json   var formatted   jObj ToString Newtonsoft Json Formatting Indented

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