Regex to validate JSON

Question

I am looking for a Regex that allows me to validate json    I am very new to Regex s and i know enough that parsing with Regex is bad but can it be used to validate

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I tried  mario s answer  but it didn t work for me  because I ve downloaded test suite from JSON org  archive  and there were 4 failed tests  fail1 json  fail18 json  fail25 json  fail27 json    I ve investigated the errors and found out  that fail1 json is actually correct  according to manual s note and RFC-7159 valid string is also a valid JSON   File fail18 json was not the case either  cause it contains actually correct deeply-nested JSON                        Too deep                        So two files left  fail25 json and fail27 json       tab character   in  string       and    line break     Both contains invalid characters  So I ve updated the pattern like this  string subpattern updated     pcreRegex                   DEFINE                  lt number gt    -       1-9  0    d     d      d      eE    -    d                      lt boolean gt    true   false   null                   lt string gt            n r t                    bfnrt           u  0-9a-f  4                         lt array gt                  amp json            amp json            s                       lt pair gt        s     amp string   s       amp json                     lt object gt                 amp pair            amp pair            s                       lt json gt     s         amp number       amp boolean       amp string       amp array       amp object     s                           A    amp json   Z            six     So now all legal tests from json org can be passed

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For  strings and numbers   I think that the partial regular expression for numbers   -    0  1-9  d        d      eE   -  d      should be instead   -    0  1-9  d        d       eE    -   d      since the decimal part of the number is optional  and also it is probably safer to escape the - symbol in   -  since it has a special meaning between brackets

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I created a Ruby implementation of Mario s solution  which does work     encoding  utf-8  module Constants   JSON VALIDATOR RE                 define subtypes and build up the json syntax  BNF-grammar-style            The  0  is a hack to simply define them as named groups here but not match on them yet            I added some atomic grouping to prevent catastrophic backtracking on invalid inputs             lt number gt   -     1-9  0    d   d     d     eE   -   d     0              lt boolean gt  true   false   null   0              lt string gt        gt                        bfnrt           u  0-9a-f  4         0              lt array gt          gt   g lt json gt         g lt json gt         s       0              lt pair gt      s   g lt string gt   s     g lt json gt    0              lt object gt         gt   g lt pair gt         g lt pair gt         s       0              lt json gt      s     gt   g lt number gt     g lt boolean gt     g lt string gt     g lt array gt     g lt object gt     s    0                A  g lt json gt   Z      uix end             inline test running if   FILE     PROGRAM NAME      support   class String     def unindent       gsub     scan       n  s    min by  l l length   u          end   end    require  test unit  unless defined  Test  Unit   class JsonValidationTest  lt  Test  Unit  TestCase     include Constants      def setup      end      def test json validator simple string       assert not nil  s    somedata   5    match JSON VALIDATOR RE      end      def test json validator deep string       long json    lt  lt -JSON unindent                    glossary                    title    example glossary              GlossDiv                        id   1918723                     boolean   true                     title    S                GlossList                            GlossEntry                                ID    SGML                    SortAs    SGML                    GlossTerm    Standard Generalized Markup Language                    Acronym    SGML                    Abbrev    ISO 8879 1986                    GlossDef                                    para    A meta-markup language  used to create markup languages such as DocBook                       GlossSeeAlso     GML    XML                                                 GlossSee    markup                                                                                        JSON        assert not nil long json match JSON VALIDATOR RE      end    end end

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Here my regexp for validate string                         bfnrt  1  u a-f0-9  4          Was written usign original syntax diagramm

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As was written above  if the language you use has a JSON-library coming with it  use it to try decoding the string and catch the exception error if it fails  If the language does not  just had such a case with FreeMarker  the following regex could at least provide some very basic validation  it s written for PHP PCRE to be testable usable for more users   It s not as foolproof as the accepted solution  but also not that scary           s             n    s        n     s   short explanation      we have two possibilities in case the string is JSON    1  the string passed is  just  a JSON object  e g    item        anotheritem    content      this can be matched by the following regex which makes sure there is at least a    at the    beginning of the string and a   at the end of the string  whatever is inbetween is not checked       s             OR  character     in the regex pattern     2  the string passed is a JSON array  e g     item    value      item    value       which would be matched by the second part of the pattern above      n    s        n         the s modifier is used to make     also match newline characters  can happen in prettyfied JSON    if I missed something that would break this unintentionally  I m grateful for comments

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Yes  a complete regex validation is possible   Most modern regex implementations allow for recursive regexpressions  which can verify a complete JSON serialized structure  The json org specification makes it quite straightforward    pcre regex              DEFINE          lt number gt    -       1-9  0    d     d      d      eE    -    d                  lt boolean gt    true   false   null           lt string gt                               bfnrt           u  0-9a-f  4                 lt array gt                  amp json            amp json            s               lt pair gt        s     amp string   s       amp json             lt object gt                 amp pair            amp pair            s               lt json gt     s         amp number       amp boolean       amp string       amp array       amp object     s           A    amp json   Z    six         It works quite well in PHP with the PCRE functions   Should work unmodified in Perl  and can certainly be adapted for other languages  Also it succeeds with the JSON test cases   Simpler RFC4627 verification  A simpler approach is the minimal consistency check as specified in RFC4627  section 6  It s however just intended as security test and basic non-validity precaution     var my JSON object                0-9  - Eaeflnr-u  n r t   test           text replace                  g         amp  amp       eval       text

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I realize that this is from over 6 years ago  However  I think there is a solution that nobody here has mentioned that is way easier than regexing   function isAJSON string        try           JSON parse string          catch e            if e instanceof SyntaxError  return false               return true

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A trailing comma in a JSON array caused my Perl 5 16 to hang  possibly because it kept backtracking   I had to add a backtrack-terminating directive      lt json gt     s         amp number       amp boolean       amp string       amp array       amp object     PRUNE   s                                                                                                  This way  once it identifies a construct that is not  optional     or     it shouldn t try backtracking over it to try to identify it as something else

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Because of the recursive nature of JSON  nested      -s   regex is not suited to validate it   Sure  some regex flavours can recursively match patterns   and can therefor match JSON   but the resulting patterns are horrible to look at  and should never ever be used in production code IMO     Beware though  many regex implementations do not support recursive patterns  Of the popular programming languages  these support recursive patterns  Perl   NET  PHP and Ruby 1 9 2

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Regex that validate simple JSON not JSONArray  it validate key string  value string integer   key value   key value    key value         s  n s      w      s     w    d       s  n s      w      s     w    w      d 1       s  n s       s  n s      w      s      w    d 1         s  n s    w      s     w    d 1       s  n       1   s  n s      s  n s      s  n s      w      s      w    d 1         s  n s    w      s     w    d 1       s  n          s  n s           s  n s    w      s     w    w      d 1       s  n s       s  n s      w      s      w    d 1         s  n s    w      s     w    d 1       s  n       1   s  n s      s  n s      s  n s      w      s      w    d 1         s  n s    w       w    d 1       s  n          s  n s         s  n s      1        s  n s    w      s     w    d       s  n s      w      s     w    w      d 1       s  n s       s  n s      w      s      w    d 1         s  n s    w      s     w    d 1       s  n       1   s  n s      s  n s      s  n s      w      s      w    d 1         s  n s    w      s     w    d 1       s  n          s  n s           s  n s    w      s     w    w      d 1       s  n s       s  n s      w      s      w    d 1         s  n s    w      s     w    d 1       s  n       1   s  n s      s  n s      s  n s      w      s      w    d 1         s  n s    w       w    d 1       s  n          s  n s         s  n s      1      s  n        sample data that validate by this JSON     key   string    key   56   key             attr   integer            attr   12             key             key                                   attr   4                   attr    string

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Looking at the documentation for JSON  it seems that the regex can simply be three parts if the goal is just to check for fitness    The string starts and ends with either    or            1          1   and   The character is an allowed JSON control character  just one                0-9  - Eaeflnr-u  n r t      or The set of characters contained in a                      All together        1           0-9  - Eaeflnr-u  n r t               1   If the JSON string contains newline characters  then you should use the singleline switch on your regex flavor so that   matches newline  Please note that this will not fail on all bad JSON  but it will fail if the basic JSON structure is invalid  which is a straight-forward way to do a basic sanity validation before passing it to a parser

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Yes  it s a common misconception that Regular Expressions can match only regular languages  In fact  the PCRE functions can match much more than regular languages  they can match even some non-context-free languages  Wikipedia s article on RegExps has a special section about it   JSON can be recognized using PCRE in several ways   mario showed one great solution using named subpatterns and back-references  Then he noted that there should be a solution using recursive patterns   R   Here is an example of such regexp written in PHP    regexString                          bfnrt        u 0-9a-f  4        regexNumber    -     1-9  0    d   d     d     eE   -   d       regexBoolean   true false null      these are actually copied from Mario s answer  regex      A    regexString      regexNumber      regexBoolean           string  number  boolean  regex           1       1      s         arrays  regex          s    regexString   s    1      s    regexString   s    1      s           objects  regex      Z is     I m using   1  instead of   R  because the latter references the entire pattern  but we have  A and  Z sequences that should not be used inside subpatterns    1  references to the regexp marked by the outermost parentheses  this is why the outermost     does not start with      So  the RegExp becomes 268 characters long       A                 bfnrt      u 0-9a-f  4     -     1-9  0    d   d     d     eE   -   d    true false null        1       1      s          s                 bfnrt      u 0-9a-f  4     s    1      s                 bfnrt      u 0-9a-f  4     s    1      s     Z is   Anyway  this should be treated as a  technology demonstration   not as a practical solution  In PHP I ll validate the JSON string with calling the json decode   function  just like  Epcylon noted   If I m going to use that JSON  if it s validated   then this is the best method

[regex] Regex to validate JSON

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