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?

Answer 1

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)
     (?<number>   -? (?= [1-9]|0(?!d) ) d+ (.d+)? ([eE] [+-]? d+)? )    
     (?<boolean>   true | false | null )
     (?<string>    " ([^"\\]* | \\ ["\\bfnrt/] | \\ u [0-9a-f]{4} )* " )
     (?<array>     [  (?:  (?&json)  (?: , (?&json)  )*  )?  s* ] )
     (?<pair>      s* (?&string) s* : (?&json)  )
     (?<object>    {  (?:  (?&pair)  (?: , (?&pair)  )*  )?  s* } )
     (?<json>   s* (?: (?&number) | (?&boolean) | (?&string) | (?&array) | (?&object) ) s* )
  )
  A (?&json) 
  /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 

]/.test(
         text.replace(/"(\.|[^"\])*"/g, ''))) &&
     eval('(' + text + ')');