Fastest way to check if a string is JSON in PHP

Question

I need a really  really fast method of checking if a string is JSON or not  I feel like this is not the best way   function isJson  string        return   is string  string   amp  amp               is object json decode  string                  is array json decode  string        true   false      Any performance enthusiasts out there want to improve this method

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I found this question after coming across something similar in my work  yesterday  My solution in the end was a hybrid of some of the approaches above  function is JSON  string       return  is null json decode  string  TRUE      FALSE   TRUE

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Easy method is to check the json result     result    json decode  json true       if  is array  result             echo  JSON is valid        else          echo  JSON is not valid

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Earlier i was just checking for a null value  which was wrong actually        data    ahad        r data   json decode  data       if  r data    json decode will return null  which is the behavior we expect           success         The above piece of code works fine with strings  However as soon as i provide number  it breaks up for example        data    1213145        r data   json decode  data        if  r data    json decode will return 1213145  which is the behavior we don t expect           success         To fix it what i did was very simple        data    ahad        r data   json decode  data        if   r data     data   amp  amp   r data          print  Json success       else         print  Json error

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Here s a performant and simple function I created  which uses basic string validation before using json decode for larger strings    function isJson  string         response   false       if           is string  string   amp  amp            string   trim  string    amp  amp            stringLength   strlen  string    amp  amp                                          stripos  string           0  amp  amp                   stripos  string       -1    1       stringLength                                                stripos  string            0  amp  amp                   stripos  string        -1    2       stringLength                          amp  amp            decodedString   json decode  string  true    amp  amp          is array  decodedString                   response   true             return  response

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This will do it   function isJson  string         decoded   json decode  string      decode our JSON string     if    is object  decoded   amp  amp   is array  decoded                         If our string doesn t produce an object or array         it s invalid  so we should return false                    return false                   If the following line resolves to true  then there was     no error and our JSON is valid  so we return true      Otherwise it isn t  so we return false             return  json last error      JSON ERROR NONE      if   isJson  someJsonString          echo  valid JSON     else       echo  not valid JSON       As shown in other answers  json last error   returns any error from our last json decode    However there are some edge use cases where this function alone is not comprehensive enough  For example  if you json decode   an integer  eg  123   or a string of numbers with no spaces or other characters  eg   123    the json last error   function will not catch an error   To combat this  I ve added an extra step that ensures the result of our json decode   is either an object or an array  If it s not  then we return false   To see this in action  check these two examples    Only check with json last error   Checking for object array first

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We need to check if passed string is not numeric because in this case json decode raises no error   function isJson  str         result   false      if   preg match     d      trim  str              json decode  str            result    json last error      JSON ERROR NONE              return  result

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Should be something like this    function isJson  string            1  Speed up the checking  amp  prevent exception throw when non string is passed     if  is numeric  string              is string  string               string            return false              cleaned str   trim  string       if    cleaned str     in array  cleaned str 0                          return false                2  Actual checking      str   json decode  string       return  json last error      JSON ERROR NONE   amp  amp   str  amp  amp   str     string      UnitTest  public function testIsJson          non json values              12           0          1          12          -1                      null          0 1                                     true          false                                                                                      json values                              foo    bar                                                                foreach   non json values as  non json value             is json   isJson  non json value            this- gt assertFalse  is json              foreach   json values as  json value             is json   isJson  json value            this- gt assertTrue  is json

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This is what I recommend if   in array substr  string  0  1                   in array substr  string  -1                    return false    else     json decode  string     return  json last error       JSON ERROR NONE

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function is json  str        return json decode  str     null      http   tr php net manual en function json-decode php return value is null when invalid encoding detected

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Answer to the Question   The function json last error returns the last error occurred during the JSON encoding and decoding  So the fastest way to check the valid JSON is     decode the JSON data    set second parameter boolean TRUE for associative array output   result   json decode  json    if  json last error       JSON ERROR NONE           JSON is valid       OR this is equivalent  if  json last error       0           JSON is valid     Note that json last error is supported in PHP    5 3 0 only      Full program to check the exact ERROR   It is always good to know the exact error during the development time  Here is full program to check the exact error based on PHP docs   function json validate  string           decode the JSON data      result   json decode  string           switch and check possible JSON errors     switch  json last error              case JSON ERROR NONE               error          JSON is valid    No error has occurred             break          case JSON ERROR DEPTH               error    The maximum stack depth has been exceeded                break          case JSON ERROR STATE MISMATCH               error    Invalid or malformed JSON                break          case JSON ERROR CTRL CHAR               error    Control character error  possibly incorrectly encoded                break          case JSON ERROR SYNTAX               error    Syntax error  malformed JSON                break             PHP  gt   5 3 3         case JSON ERROR UTF8               error    Malformed UTF-8 characters  possibly incorrectly encoded                break             PHP  gt   5 5 0         case JSON ERROR RECURSION               error    One or more recursive references in the value to be encoded                break             PHP  gt   5 5 0         case JSON ERROR INF OR NAN               error    One or more NAN or INF values in the value to be encoded                break          case JSON ERROR UNSUPPORTED TYPE               error    A value of a type that cannot be encoded was given                break          default               error    Unknown JSON error occured                break             if   error                      throw the Exception or exit    or whatever            exit  error                 everything is OK     return  result         Testing with Valid JSON INPUT    json       user id  13  username   stack     user id  14  username   over       output   json validate  json   print r  output        Valid OUTPUT   Array        0    gt  stdClass Object                        user id    gt  13              username    gt  stack                 1    gt  stdClass Object                        user id    gt  14              username    gt  over                  Testing with invalid JSON    json     background-color yellow color  000 padding 10px width 650px      output   json validate  json   print r  output        Invalid OUTPUT   Syntax error  malformed JSON       Extra note for  PHP    5 2  amp  amp  PHP  lt  5 3 0    Since json last error is not supported in PHP 5 2  you can check if the encoding or decoding returns boolean FALSE  Here is an example     decode the JSON data  result   json decode  json   if   result     FALSE           JSON is invalid     Hope this is helpful  Happy Coding

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Hi here s a little snippet from my library  in this first condition I m just checking if the data is json then return it if correctly decoded  please note the substr usage for performance   I haven t seen yet any json file not begining neither by   or     input trim  input   if   substr  input  0  1          amp  amp  substr  input  -1          or  substr  input  0  1          amp  amp  substr  input  -1                  output   json decode  input  1       if  in array gettype  output    object   array                then it s definitely JSON

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Using PHPBench with the following class  the below results were achieved   lt  php  declare strict types 1            Revs 1000      Iterations 100      class BenchmarkJson       public function benchCatchValid    bool                validJson      quot validJson quot  true            try               json decode  validJson  true  512  JSON THROW ON ERROR               return true            catch  JsonException  exception             return false             public function benchCatchInvalid    bool                invalidJson      quot invalidJson quot            try               json decode  invalidJson  true  512  JSON THROW ON ERROR               return true            catch  JsonException  exception             return false             public function benchLastErrorValid    bool                validJson      quot validJson quot  true            json decode  validJson  true           return  json last error       JSON ERROR NONE              public function benchLastErrorInvalid    bool                invalidJson      quot invalidJson quot            json decode  invalidJson  true           return  json last error       JSON ERROR NONE              public function benchNullValid    bool                validJson      quot validJson quot  true            return  json decode  validJson  true      null              public function benchNullInvalid    bool                invalidJson      quot invalidJson quot            return  json decode  invalidJson  true      null             6 subjects  600 iterations  6 000 revs  0 rejects  0 failures  0 warnings  best  mean mode  worst    0 714  1 203 1 175  1 073    s   T  721 504  s   SD r 0 089  s   RSD r  7 270  suite  1343ab9a3590de6065bc0bc6eeb344c9f6eba642  date  2020-01-21  stime  12 50 14  --------------- ----------------------- ----- ------ ----- ------------ --------- --------- --------- --------- --------- -------- -------    benchmark       subject                 set   revs   its   mem peak     best      mean      mode      worst     stdev     rstdev   diff     --------------- ----------------------- ----- ------ ----- ------------ --------- --------- --------- --------- --------- -------- -------    BenchmarkJson   benchCatchValid         0     1000   100   2 980 168b   0 954  s   1 032  s   1 016  s   1 428  s   0 062  s   6 04     1 33x     BenchmarkJson   benchCatchInvalid       0     1000   100   2 980 184b   2 033  s   2 228  s   2 166  s   3 001  s   0 168  s   7 55     2 88x     BenchmarkJson   benchLastErrorValid     0     1000   100   2 980 184b   1 076  s   1 195  s   1 169  s   1 616  s   0 083  s   6 97     1 54x     BenchmarkJson   benchLastErrorInvalid   0     1000   100   2 980 184b   0 785  s   0 861  s   0 863  s   1 132  s   0 056  s   6 54     1 11x     BenchmarkJson   benchNullValid          0     1000   100   2 980 168b   0 985  s   1 124  s   1 077  s   1 731  s   0 114  s   10 15    1 45x     BenchmarkJson   benchNullInvalid        0     1000   100   2 980 184b   0 714  s   0 775  s   0 759  s   1 073  s   0 049  s   6 36     1 00x    --------------- ----------------------- ----- ------ ----- ------------ --------- --------- --------- --------- --------- -------- -------    Conclusion  The fastest way to check if json is valid is to return json decode  json  true      null

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r    array json decode  arr   if  is array  r     count  r   lt  1  return false

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Tested thoroughly  Should do the job  public static function is json string  json  bool       json decode  json       if  json last error       JSON ERROR NONE            return true            return false

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Another simple way  function is json  str        return is array json decode  str true

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function is json  input          input   trim  input        if  substr  input 0 1       OR substr  input -1 1                return false       return is array  json decode  input  true

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Another suggestion from me     function isJson string  string      return   result   json decode  string  true      result    string

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I ve tried some of those solution but nothing was working for me  I try this simple thing     isJson   json decode  myJSON    if   isJson instanceof  stdClass    is array  isJson        echo  it s JSON confirmed      else      echo  nope        I think it s a fine solutiuon since JSON decode without the second parameter give an object   EDIT   If you know what will be the input  you can adapt this code to your needs  In my case I know I have a Json wich begin by      so i don t need to check if it s an array

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function isJson  string     json decode  string    return  json last error      JSON ERROR NONE

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Expanding on this answer How about the following    lt  php       json       user id  13  username   stack     user id  14  username   over             json    12        function isJson  string            json decode  string           if json last error      JSON ERROR NONE                if substr  string 0 1          amp  amp  substr  string -1            return TRUE                else if substr  string 0 1          amp  amp  substr  string -1            return TRUE                else   return FALSE                         echo isJson  json     gt

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The simplest and fastest way that I use is following   json array   json decode   raw json   true     if   json array    NULL       check if it was invalid json string     die   Invalid        Invalid JSON error      you can execute some else condition over here in case of valid JSON  It is because  json decode   returns NULL if the entered string is not json or invalid json   Simple function to validate JSON If you have to validate your JSON in multiple places  you can always use the following function  function is valid json   raw json        return   json decode   raw json   true      NULL     false   true      Yes  thats it     In the above function  you will get true in return if it is a valid JSON

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All you really need to do is this     if  is object json decode  MyJSONArray                do something         This request does not require a separate function even  Just wrap is object around json decode and move on  Seems this solution has people putting way too much thought into it

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This will return true if your string represents a json array or object   function isJson  str         json   json decode  str       return  json  amp  amp   str     json      It rejects json strings that only contains a number  string or boolean  although those strings are technically valid json   var dump isJson    a  5         bool true  var dump isJson   1 2 3         bool true  var dump isJson  1        bool false  var dump isJson  1 5        bool false  var dump isJson  true        bool false  var dump isJson  false        bool false  var dump isJson  null        bool false  var dump isJson  hello        bool false  var dump isJson          bool false    It is the shortest way I can come up with

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Freshly-made function for PHP 5 2 compatibility  if you need the decoded data on success   function try json decode   json   amp   success   null         non-strings may cause warnings   if   is string   json          success   false      return  json          data   json decode   json          output arg    success           non-null data  success       data      null             null data from  null  json  success       json      null             null data from    null    json padded with whitespaces  success      preg match     s null s       json          return decoded or original data   return  success    data    json      Usage    json or not          data   try json decode   json or not   success     if   success        process data   data    else what the hell is it   data      Some tests   var dump  try json decode  array     success     success       ret   array 0      success    bool false   var dump  try json decode  123   success     success       ret   int 123    success    bool false   var dump  try json decode            success     success       ret   string 6             success    bool false   var dump  try json decode  null   success     success       ret   NULL   success    bool false   var dump  try json decode  null    success     success       ret   NULL   success    bool true   var dump  try json decode    null      success     success       ret   NULL   success    bool true   var dump  try json decode    true      success     success       ret   bool true    success    bool true   var dump  try json decode     hello       success     success       ret   string 5   hello    success    bool true   var dump  try json decode      a  123       success     success       ret   object stdClass  2  1      a    gt  int 123      success    bool true

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Using json decode to  probe  it might not actually be the fastest way  If it s a deeply nested structure  then instantiating a lot of objects of arrays to just throw them away is a waste of memory and time    So it might be faster to use preg match and the RFC4627 regex to also ensure validity        in JS    var my JSON object                0-9  - Eaeflnr-u  n r t   test           text replace                  g           The same in PHP     return  preg match               0-9   - Eaeflnr-u   n  r  t            preg replace                             json string      Not enough of a performance enthusiast to bother with benchmarks here however

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You must validate your input to make sure the string you pass is not empty and is  in fact  a string  An empty string is not valid JSON   function is json  string      return  empty  string   amp  amp  is string  string   amp  amp  is array json decode  string  true    amp  amp  json last error      0      I think in PHP it s more important to determine if the JSON object even has data  because to use the data you will need to call json encode   or json decode    I suggest denying empty JSON objects so you aren t unnecessarily running encodes and decodes on empty data   function has json data  string       array   json decode  string  true     return  empty  string   amp  amp  is string  string   amp  amp  is array  array   amp  amp   empty  array   amp  amp  json last error      0

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A simple modification to henrik s answer to touch most required possibilities      including      and         function isValidJson  string        json decode  string       if json last error      JSON ERROR NONE             if   string 0             string 0                           first    string  0                if  substr  string  -1            substr  string  -1                              last   substr  string  -1                    if  first         amp  amp   last                              return true                                     if  first         amp  amp   last                              return true                                     return false                             return false                     return false             return false

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I don t know about performance or elegance of my solution  but it s what I m using   if  preg match                 string          aJson   json decode  string  true       if   is null  aJson                do stuff here               Since all my JSON encoded strings start with    it suffices to test for this with a RegEx  I m not at all fluent with RegEx  so there might be a better way to do this  Also  strpos   might be quicker   Just trying to give in my tuppence worth   P S  Just updated the RegEx string to             to also find JSON array strings  So it now looks for either    or    at the beginning of the string

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The custom function  function custom json decode  amp  contents NULL   normalize contents true   force array true          ---------------decode contents---------------------       decoded contents NULL       if is string  contents              decoded contents json decode  contents  force array                 ---------------normalize contents---------------------      if  normalize contents   true            if is string  decoded contents                 if  decoded contents    NULL    decoded contents    null                      contents NULL                            elseif  decoded contents    FALSE    decoded contents    false                      contents false                                  elseif  is null  decoded contents                  contents  decoded contents                      else             ---------------validation contents---------------------           contents  decoded contents             return  contents      Cases   none json str  hello      ------------decoding a none json str---------------   contents custom json decode  none json str      returns  hello     ------------checking a none json str---------------  custom json decode  none json str false     valid json false   if  is null  none json str          valid json true       Resources  https   gist github com rafasashi 93d06bae83cc1a1f440b

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The fastest way is to  quot maybe decode quot  the possible JSON string Is this really the fastest method  If you want to decode complex objects or larger arrays  this is the fastest way  by far  If your json string contains short values  like scalars or objects with only 1-2 attributes  then all solutions in this SO questions come to a similar performance  Here is a performance comparison that I ve done with some dummy and real-live JSON values  PHP version  7 4 12 1   Duration  1 5828 sec   60 000 calls   json last error      JSON ERROR NONE 2   Duration  1 5202 sec   60 000 calls   is object  json decode     3   Duration  1 5400 sec   60 000 calls   json decode    amp  amp   res     string 4   Duration  1 3536 sec   60 000 calls   preg match   5   Duration  0 2261 sec   60 000 calls    quot maybe decode quot  approach  The last line is the code from this answer  which is the  quot maybe decode quot  approach  Here is the performance comparison script  there you can see the test-data I used for the comparison  https   gist github com stracker-phil 6a80e6faedea8dab090b4bf6668ee461  The  quot maybe decode quot  logic code We first perform some type checks and string comparisons before attempting to decode the JSON string  This gives us the best performance because json decode   can be slow         Returns true  when the given parameter is a valid JSON string      function is json   value            A non-string value can never be a JSON string      if     is string   value       return false            Numeric strings are always valid JSON      if   is numeric   value       return true            Any non-numeric JSON string must be longer than 2 characters      if   strlen   value    lt  2     return false             quot null quot  is valid JSON string      if    null       value     return true             quot true quot  and  quot false quot  are valid JSON strings      if    true       value     return true        if    false       value     return false            Any other JSON string has to be wrapped in        or  quot  quot       if           value 0   amp  amp          value 0   amp  amp    quot       value 0      return false            Note the last param  1   this limits the depth to the first level       json data   json decode   value  null  1            When json decode fails  it returns NULL      if   is null   json data       return false        return true      Extra  Use this logic to safely double-decode JSON This function uses the same logic but either returns the decoded JSON object or the original value  I use this function in a parser that recursively decodes a complex object  Some attributes might be decoded already by an earlier iteration  That function recognizes this and does not attempt to double decode the value again         Tests  if the given  value parameter is a JSON string     When it is a valid JSON value  the decoded value is returned     When the value is no JSON value  i e  it was decoded already   then     the original value is returned      function get data   value   as object   false         if     is string   value       return  value        if   is numeric   value       return 0    value        if   strlen   value    lt  2     return  value        if    null       value     return null        if    true       value     return true        if    false       value     return false        if           value 0   amp  amp          value 0   amp  amp    quot       value 0      return  value          json data   json decode   value   as object        if   is null   json data       return  value        return  json data     Note  When passing a non-string to any other solution in this SO question  you will get dramatically degraded performance   wrong return values  or even fatal errors   This code is bulletproof and highly performant

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in GuzzleHttp          Wrapper for json decode that throws when an error occurs         param string  json    JSON data to parse     param bool  assoc     When true  returned objects will be converted                           into associative arrays      param int     depth   User specified recursion depth      param int     options Bitmask of JSON decode options         return mixed     throws  InvalidArgumentException if the JSON cannot be decoded      link http   www php net manual en function json-decode php     function json decode  json   assoc   false   depth   512   options   0         data    json decode  json   assoc   depth   options       if  JSON ERROR NONE     json last error              throw new  InvalidArgumentException               json decode error      json last error msg                return  data            Wrapper for JSON encoding that throws when an error occurs         param mixed  value   The value being encoded     param int     options JSON encode option bitmask     param int     depth   Set the maximum depth  Must be greater than zero         return string     throws  InvalidArgumentException if the JSON cannot be encoded      link http   www php net manual en function json-encode php     function json encode  value   options   0   depth   512         json    json encode  value   options   depth       if  JSON ERROR NONE     json last error              throw new  InvalidArgumentException               json encode error      json last error msg                return  json

[php] Fastest way to check if a string is JSON in PHP?

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