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
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) \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, ''))) &&
eval('(' + text + ')');