JSON - JSON encoder/decoder


JSON - JSON (JavaScript Object Notation) encoder/decoder


 use JSON; # imports encode_json, decode_json, to_json and from_json.
 $json_text   = to_json($perl_scalar);
 $perl_scalar = from_json($json_text);
 # option-acceptable
 $json_text   = to_json($perl_scalar, {ascii => 1});
 $perl_scalar = from_json($json_text, {utf8 => 1});
 # OOP
 $json = new JSON;
 $json_text   = $json->encode($perl_scalar);
 $perl_scalar = $json->decode($json_text);
 # pretty-printing
 $json_text = $json->pretty->encode($perl_scalar);
 # simple interface
 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
 $perl_hash_or_arrayref  = decode_json $utf8_encoded_json_text;
 # If you want to use PP only support features, call with '-support_by_pp'
 # When XS unsupported feature is enable, using PP de/encode.
 use JSON -support_by_pp;



This version is compatible with JSON::XS 2.2.


 ************************** CAUTION ********************************
 * This is 'JSON module version 2' and there are many differences  *
 * to version 1.xx                                                 *
 * Please check your applications useing old version.              *
 *   See to 'INCOMPATIBLE CHANGES TO OLD VERSION'                  *

JSON (JavaScript Object Notation) is a simple data format. See to http://www.json.org/ and RFC4627(http://www.ietf.org/rfc/rfc4627.txt).

This module converts Perl data structures to JSON and vice versa using either the JSON::XS manpage or the JSON::PP manpage.

JSON::XS is the fastest and most proper JSON module on CPAN which must be compiled and installed in your environment. JSON::PP is a pure-Perl module which is bundled in this distribution and has a strong compatibility to JSON::XS.

This module try to use JSON::XS by default and fail to it, use JSON::PP instead. So its features completely depend on JSON::XS or JSON::PP.


To distinguish the module name 'JSON' and the format type JSON, the former is quoted by C<> (its results vary with your using media), and the latter is left just as it is.

Module name : JSON

Format type : JSON



Some documents are copied and modified from FUNCTIONAL INTERFACE in the JSON::XS manpage. to_json and from_json are additional functions.


   $json_text = to_json($perl_scalar)

Converts the given Perl data structure to a json string.

This function call is functionally identical to:

   $json_text = JSON->new->encode($perl_scalar)

Takes a hash reference as the second.

   $json_text = to_json($perl_scalar, $flag_hashref)


   $json_text = encode_json($perl_scalar, {utf8 => 1, pretty => 1})

equivalent to:

   $json_text = JSON->new->utf8(1)->pretty(1)->encode($perl_scalar)


   $perl_scalar = from_json($json_text)

The opposite of to_json: expects a json string and tries to parse it, returning the resulting reference.

This function call is functionally identical to:

    $perl_scalar = JSON->decode($json_text)

Takes a hash reference as the second.

    $perl_scalar = from_json($json_text, $flag_hashref)


    $perl_scalar = from_json($json_text, {utf8 => 1})

equivalent to:

    $perl_scalar = JSON->new->utf8(1)->decode($json_text)


    $json_text = encode_json $perl_scalar

Converts the given Perl data structure to a UTF-8 encoded, binary string.

This function call is functionally identical to:

    $json_text = JSON->new->utf8->encode($perl_scalar)


    $perl_scalar = decode_json $json_text

The opposite of encode_json: expects an UTF-8 (binary) string and tries to parse that as an UTF-8 encoded JSON text, returning the resulting reference.

This function call is functionally identical to:

    $perl_scalar = JSON->new->utf8->decode($json_text)


    $is_boolean = JSON::is_bool($scalar)

Returns true if the passed scalar represents either JSON::true or JSON::false, two constants that act like 1 and 0 respectively and are also used to represent JSON true and false in Perl strings.


Returns JSON true value which is blessed object. It isa JSON::Boolean object.


Returns JSON false value which is blessed object. It isa JSON::Boolean object.


Returns undef.

See MAPPING, below, for more information on how JSON values are mapped to Perl.



    $json = new JSON

Returns a new JSON object inherited from either JSON::XS or JSON::PP that can be used to de/encode JSON strings.

All boolean flags described below are by default disabled.

The mutators for flags all return the JSON object again and thus calls can be chained:

   my $json = JSON->new->utf8->space_after->encode({a => [1,2]})
   => {"a": [1, 2]}


    $json = $json->ascii([$enable])
    $enabled = $json->get_ascii

If $enable is true (or missing), then the encode method will not generate characters outside the code range 0..127. Any Unicode characters outside that range will be escaped using either a single \uXXXX or a double \uHHHH\uLLLLL escape sequence, as per RFC4627.

If $enable is false, then the encode method will not escape Unicode characters unless required by the JSON syntax or other flags. This results in a faster and more compact format.

This feature depends on the used Perl version and environment.

See to UNICODE HANDLING ON PERLS in the JSON::PP manpage if the backend is PP.

  JSON->new->ascii(1)->encode([chr 0x10401])
  => ["\ud801\udc01"]


    $json = $json->latin1([$enable])
    $enabled = $json->get_latin1

If $enable is true (or missing), then the encode method will encode the resulting JSON text as latin1 (or iso-8859-1), escaping any characters outside the code range 0..255.

If $enable is false, then the encode method will not escape Unicode characters unless required by the JSON syntax or other flags.

  JSON->new->latin1->encode (["\x{89}\x{abc}"]
  => ["\x{89}\\u0abc"]    # (perl syntax, U+abc escaped, U+89 not)


    $json = $json->utf8([$enable])
    $enabled = $json->get_utf8

If $enable is true (or missing), then the encode method will encode the JSON result into UTF-8, as required by many protocols, while the decode method expects to be handled an UTF-8-encoded string. Please note that UTF-8-encoded strings do not contain any characters outside the range 0..255, they are thus useful for bytewise/binary I/O.

In future versions, enabling this option might enable autodetection of the UTF-16 and UTF-32 encoding families, as described in RFC4627.

If $enable is false, then the encode method will return the JSON string as a (non-encoded) Unicode string, while decode expects thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs to be done yourself, e.g. using the Encode module.

Example, output UTF-16BE-encoded JSON:

  use Encode;
  $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);

Example, decode UTF-32LE-encoded JSON:

  use Encode;
  $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);

See to UNICODE HANDLING ON PERLS in the JSON::PP manpage if the backend is PP.


    $json = $json->pretty([$enable])

This enables (or disables) all of the indent, space_before and space_after (and in the future possibly more) flags in one call to generate the most readable (or most compact) form possible.

Equivalent to:


The indent space length is three and JSON::XS cannot change the indent space length.


    $json = $json->indent([$enable])
    $enabled = $json->get_indent

If $enable is true (or missing), then the encode method will use a multiline format as output, putting every array member or object/hash key-value pair into its own line, identing them properly.

If $enable is false, no newlines or indenting will be produced, and the resulting JSON text is guarenteed not to contain any newlines.

This setting has no effect when decoding JSON texts.

The indent space length is three. With JSON::PP, you can also access indent_length to change indent space length.


    $json = $json->space_before([$enable])
    $enabled = $json->get_space_before

If $enable is true (or missing), then the encode method will add an extra optional space before the : separating keys from values in JSON objects.

If $enable is false, then the encode method will not add any extra space at those places.

This setting has no effect when decoding JSON texts.

Example, space_before enabled, space_after and indent disabled:

   {"key" :"value"}


    $json = $json->space_after([$enable])
    $enabled = $json->get_space_after

If $enable is true (or missing), then the encode method will add an extra optional space after the : separating keys from values in JSON objects and extra whitespace after the , separating key-value pairs and array members.

If $enable is false, then the encode method will not add any extra space at those places.

This setting has no effect when decoding JSON texts.

Example, space_before and indent disabled, space_after enabled:

   {"key": "value"}


    $json = $json->relaxed([$enable])
    $enabled = $json->get_relaxed

If $enable is true (or missing), then decode will accept some extensions to normal JSON syntax (see below). encode will not be affected in anyway. Be aware that this option makes you accept invalid JSON texts as if they were valid!. I suggest only to use this option to parse application-specific files written by humans (configuration files, resource files etc.)

If $enable is false (the default), then decode will only accept valid JSON texts.

Currently accepted extensions are:


    $json = $json->canonical([$enable])
    $enabled = $json->get_canonical

If $enable is true (or missing), then the encode method will output JSON objects by sorting their keys. This is adding a comparatively high overhead.

If $enable is false, then the encode method will output key-value pairs in the order Perl stores them (which will likely change between runs of the same script).

This option is useful if you want the same data structure to be encoded as the same JSON text (given the same overall settings). If it is disabled, the same hash might be encoded differently even if contains the same data, as key-value pairs have no inherent ordering in Perl.

This setting has no effect when decoding JSON texts.


    $json = $json->allow_nonref([$enable])
    $enabled = $json->get_allow_nonref

If $enable is true (or missing), then the encode method can convert a non-reference into its corresponding string, number or null JSON value, which is an extension to RFC4627. Likewise, decode will accept those JSON values instead of croaking.

If $enable is false, then the encode method will croak if it isn't passed an arrayref or hashref, as JSON texts must either be an object or array. Likewise, decode will croak if given something that is not a JSON object or array.

   JSON->new->allow_nonref->encode ("Hello, World!")
   => "Hello, World!"


    $json = $json->allow_unknown ([$enable])
    $enabled = $json->get_allow_unknown

If $enable is true (or missing), then ``encode'' will *not* throw an exception when it encounters values it cannot represent in JSON (for example, filehandles) but instead will encode a JSON ``null'' value. Note that blessed objects are not included here and are handled separately by c<allow_nonref>.

If $enable is false (the default), then ``encode'' will throw an exception when it encounters anything it cannot encode as JSON.

This option does not affect ``decode'' in any way, and it is recommended to leave it off unless you know your communications partner.


    $json = $json->allow_blessed([$enable])
    $enabled = $json->get_allow_blessed

If $enable is true (or missing), then the encode method will not barf when it encounters a blessed reference. Instead, the value of the convert_blessed option will decide whether null (convert_blessed disabled or no TO_JSON method found) or a representation of the object (convert_blessed enabled and TO_JSON method found) is being encoded. Has no effect on decode.

If $enable is false (the default), then encode will throw an exception when it encounters a blessed object.


    $json = $json->convert_blessed([$enable])
    $enabled = $json->get_convert_blessed

If $enable is true (or missing), then encode, upon encountering a blessed object, will check for the availability of the TO_JSON method on the object's class. If found, it will be called in scalar context and the resulting scalar will be encoded instead of the object. If no TO_JSON method is found, the value of allow_blessed will decide what to do.

The TO_JSON method may safely call die if it wants. If TO_JSON returns other blessed objects, those will be handled in the same way. TO_JSON must take care of not causing an endless recursion cycle (== crash) in this case. The name of TO_JSON was chosen because other methods called by the Perl core (== not by the user of the object) are usually in upper case letters and to avoid collisions with the to_json function or method.

This setting does not yet influence decode in any way.

If $enable is false, then the allow_blessed setting will decide what to do when a blessed object is found.

convert_blessed_universally mode
If use JSON with -convert_blessed_universally, the UNIVERSAL::TO_JSON subroutine is defined as the below code:
   *UNIVERSAL::TO_JSON = sub {
       my $b_obj = B::svref_2object( $_[0] );
       return    $b_obj->isa('B::HV') ? { %{ $_[0] } }
               : $b_obj->isa('B::AV') ? [ @{ $_[0] } ]
               : undef

This will cause that encode method converts simple blessed objects into JSON objects as non-blessed object.

   JSON -convert_blessed_universally;
   $json->allow_blessed->convert_blessed->encode( $blessed_object )

This feature is experimental and may be removed in the future.


    $json = $json->filter_json_object([$coderef])

When $coderef is specified, it will be called from decode each time it decodes a JSON object. The only argument passed to the coderef is a reference to the newly-created hash. If the code references returns a single scalar (which need not be a reference), this value (i.e. a copy of that scalar to avoid aliasing) is inserted into the deserialised data structure. If it returns an empty list (NOTE: not undef, which is a valid scalar), the original deserialised hash will be inserted. This setting can slow down decoding considerably.

When $coderef is omitted or undefined, any existing callback will be removed and decode will not change the deserialised hash in any way.

Example, convert all JSON objects into the integer 5:

   my $js = JSON->new->filter_json_object (sub { 5 });
   # returns [5]
   $js->decode ('[{}]'); # the given subroutine takes a hash reference.
   # throw an exception because allow_nonref is not enabled
   # so a lone 5 is not allowed.
   $js->decode ('{"a":1, "b":2}');


    $json = $json->filter_json_single_key_object($key [=> $coderef])

Works remotely similar to filter_json_object, but is only called for JSON objects having a single key named $key.

This $coderef is called before the one specified via filter_json_object, if any. It gets passed the single value in the JSON object. If it returns a single value, it will be inserted into the data structure. If it returns nothing (not even undef but the empty list), the callback from filter_json_object will be called next, as if no single-key callback were specified.

If $coderef is omitted or undefined, the corresponding callback will be disabled. There can only ever be one callback for a given key.

As this callback gets called less often then the filter_json_object one, decoding speed will not usually suffer as much. Therefore, single-key objects make excellent targets to serialise Perl objects into, especially as single-key JSON objects are as close to the type-tagged value concept as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not support this in any way, so you need to make sure your data never looks like a serialised Perl hash.

Typical names for the single object key are __class_whatever__, or $__dollars_are_rarely_used__$ or }ugly_brace_placement, or even things like __class_md5sum(classname)__, to reduce the risk of clashing with real hashes.

Example, decode JSON objects of the form { "__widget__" => <id> } into the corresponding $WIDGET{<id>} object:

   # return whatever is in $WIDGET{5}:
      ->filter_json_single_key_object (__widget__ => sub {
            $WIDGET{ $_[0] }
      ->decode ('{"__widget__": 5')
   # this can be used with a TO_JSON method in some "widget" class
   # for serialisation to json:
   sub WidgetBase::TO_JSON {
      my ($self) = @_;
      unless ($self->{id}) {
         $self->{id} = ..get..some..id..;
         $WIDGET{$self->{id}} = $self;
      { __widget__ => $self->{id} }


    $json = $json->shrink([$enable])
    $enabled = $json->get_shrink

With JSON::XS, this flag resizes strings generated by either encode or decode to their minimum size possible. This can save memory when your JSON texts are either very very long or you have many short strings. It will also try to downgrade any strings to octet-form if possible: perl stores strings internally either in an encoding called UTF-X or in octet-form. The latter cannot store everything but uses less space in general (and some buggy Perl or C code might even rely on that internal representation being used).

With JSON::PP, it is noop about resizing strings but tries utf8::downgrade to the returned string by encode. See to the utf8 manpage.

See to OBJECT-ORIENTED INTERFACE in the JSON::XS manpage and METHODS in the JSON::PP manpage.


    $json = $json->max_depth([$maximum_nesting_depth])
    $max_depth = $json->get_max_depth

Sets the maximum nesting level (default 512) accepted while encoding or decoding. If a higher nesting level is detected in JSON text or a Perl data structure, then the encoder and decoder will stop and croak at that point.

Nesting level is defined by number of hash- or arrayrefs that the encoder needs to traverse to reach a given point or the number of { or [ characters without their matching closing parenthesis crossed to reach a given character in a string.

If no argument is given, the highest possible setting will be used, which is rarely useful.

Note that nesting is implemented by recursion in C. The default value has been chosen to be as large as typical operating systems allow without crashing. (JSON::XS)

With JSON::PP as the backend, when a large value (100 or more) was set and it de/encodes a deep nested object/text, it may raise a warning 'Deep recursion on subroutin' at the perl runtime phase.

See SECURITY CONSIDERATIONS in the JSON::XS manpage for more info on why this is useful.


    $json = $json->max_size([$maximum_string_size])
    $max_size = $json->get_max_size

Set the maximum length a JSON text may have (in bytes) where decoding is being attempted. The default is 0, meaning no limit. When decode is called on a string that is longer then this many bytes, it will not attempt to decode the string but throw an exception. This setting has no effect on encode (yet).

If no argument is given, the limit check will be deactivated (same as when 0 is specified).

See SECURITY CONSIDERATIONS in the JSON::XS manpage, below, for more info on why this is useful.


    $json_text = $json->encode($perl_scalar)

Converts the given Perl data structure (a simple scalar or a reference to a hash or array) to its JSON representation. Simple scalars will be converted into JSON string or number sequences, while references to arrays become JSON arrays and references to hashes become JSON objects. Undefined Perl values (e.g. undef) become JSON null values. Neither true nor false values will be generated.


    $perl_scalar = $json->decode($json_text)

The opposite of encode: expects a JSON text and tries to parse it, returning the resulting simple scalar or reference. Croaks on error.

JSON numbers and strings become simple Perl scalars. JSON arrays become Perl arrayrefs and JSON objects become Perl hashrefs. true becomes 1, false becomes 0 and null becomes undef.


    ($perl_scalar, $characters) = $json->decode_prefix($json_text)

This works like the decode method, but instead of raising an exception when there is trailing garbage after the first JSON object, it will silently stop parsing there and return the number of characters consumed so far.

   JSON->new->decode_prefix ("[1] the tail")
   => ([], 3)



    $boolean = $json->property($property_name)

Returns a boolean value about above some properties.

The available properties are ascii, latin1, utf8, indent,space_before, space_after, relaxed, canonical, allow_nonref, allow_unknown, allow_blessed, convert_blessed, shrink, max_depth and max_size.

   $boolean = $json->property('utf8');
    => 0
   $boolean = $json->property('utf8');
    => 1

Sets the propery with a given boolean value.

    $json = $json->property($property_name => $boolean);

With no argumnt, it returns all the above properties as a hash reference.

    $flag_hashref = $json->property();


In JSON::XS 2.2, incremental parsing feature of JSON texts was experimentally implemented. Please check to INCREMENTAL PARSING in the JSON::XS manpage.

[void, scalar or list context] = $json->incr_parse ([$string])
This is the central parsing function. It can both append new text and extract objects from the stream accumulated so far (both of these functions are optional).

If $string is given, then this string is appended to the already existing JSON fragment stored in the $json object.

After that, if the function is called in void context, it will simply return without doing anything further. This can be used to add more text in as many chunks as you want.

If the method is called in scalar context, then it will try to extract exactly one JSON object. If that is successful, it will return this object, otherwise it will return undef. If there is a parse error, this method will croak just as decode would do (one can then use incr_skip to skip the errornous part). This is the most common way of using the method.

And finally, in list context, it will try to extract as many objects from the stream as it can find and return them, or the empty list otherwise. For this to work, there must be no separators between the JSON objects or arrays, instead they must be concatenated back-to-back. If an error occurs, an exception will be raised as in the scalar context case. Note that in this case, any previously-parsed JSON texts will be lost.

$lvalue_string = $json->incr_text
This method returns the currently stored JSON fragment as an lvalue, that is, you can manipulate it. This only works when a preceding call to incr_parse in scalar context successfully returned an object. Under all other circumstances you must not call this function (I mean it. although in simple tests it might actually work, it will fail under real world conditions). As a special exception, you can also call this method before having parsed anything.

This function is useful in two cases: a) finding the trailing text after a JSON object or b) parsing multiple JSON objects separated by non-JSON text (such as commas).

In Perl 5.005, lvalue attribute is not available. You must write codes like the below:

    $string = $json->incr_text;
    $string =~ s/\s*,\s*//;
    $json->incr_text( $string );

This will reset the state of the incremental parser and will remove the parsed text from the input buffer. This is useful after incr_parse died, in which case the input buffer and incremental parser state is left unchanged, to skip the text parsed so far and to reset the parse state.


The below methods are JSON::PP own methods, so when JSON works with JSON::PP (i.e. the created object is a JSON::PP object), available. See to JSON::PP OWN METHODS in the JSON::PP manpage in detail.

If you use JSON with additonal -support_by_pp, some methods are available even with JSON::XS. See to USE PP FEATURES EVEN THOUGH XS BACKEND.

   use JSON -support_by_pp;
   my $json = new JSON;
   # functional interfaces too.
   print to_json(["/"], {escape_slash => 1});
   print from_json('["foo"]', {utf8 => 1});

If you do not want to all functions but -support_by_pp, use -no_export.

   use JSON -support_by_pp, -no_export;
   # functional interfaces are not exported.


    $json = $json->allow_singlequote([$enable])

If $enable is true (or missing), then decode will accept any JSON strings quoted by single quotations that are invalid JSON format.


As same as the relaxed option, this option may be used to parse application-specific files written by humans.


    $json = $json->allow_barekey([$enable])

If $enable is true (or missing), then decode will accept bare keys of JSON object that are invalid JSON format.

As same as the relaxed option, this option may be used to parse application-specific files written by humans.



    $json = $json->allow_bignum([$enable])

If $enable is true (or missing), then decode will convert the big integer Perl cannot handle as integer into a the Math::BigInt manpage object and convert a floating number (any) into a the Math::BigFloat manpage.

On the contary, encode converts Math::BigInt objects and Math::BigFloat objects into JSON numbers with allow_blessed enable.

   $bigfloat = $json->decode('2.000000000000000000000000001');
   print $json->encode($bigfloat);
   # => 2.000000000000000000000000001

See to MAPPING aboout the conversion of JSON number.


    $json = $json->loose([$enable])

The unescaped [\x00-\x1f\x22\x2f\x5c] strings are invalid in JSON strings and the module doesn't allow to decode to these (except for \x2f). If $enable is true (or missing), then decode will accept these unescaped strings.


See to JSON::PP OWN METHODS in the JSON::PP manpage.


    $json = $json->escape_slash([$enable])

According to JSON Grammar, slash (U+002F) is escaped. But by default JSON backend modules encode strings without escaping slash.

If $enable is true (or missing), then encode will escape slashes.


    $json = $json->indent_length($length)

With JSON::XS, The indent space length is 3 and cannot be changed. With JSON::PP, it sets the indent space length with the given $length. The default is 3. The acceptable range is 0 to 15.


    $json = $json->sort_by($function_name)
    $json = $json->sort_by($subroutine_ref)

If $function_name or $subroutine_ref are set, its sort routine are used.

   $js = $pc->sort_by(sub { $JSON::PP::a cmp $JSON::PP::b })->encode($obj);
   # is($js, q|{"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9}|);
   $js = $pc->sort_by('own_sort')->encode($obj);
   # is($js, q|{"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9}|);
   sub JSON::PP::own_sort { $JSON::PP::a cmp $JSON::PP::b }

As the sorting routine runs in the JSON::PP scope, the given subroutine name and the special variables $a, $b will begin with 'JSON::PP::'.

If $integer is set, then the effect is same as canonical on.

See to JSON::PP OWN METHODS in the JSON::PP manpage.


This section is copied from JSON::XS and modified to JSON. JSON::XS and JSON::PP mapping mechanisms are almost equivalent.

See to MAPPING in the JSON::XS manpage.


A JSON object becomes a reference to a hash in Perl. No ordering of object keys is preserved (JSON does not preserver object key ordering itself).

A JSON array becomes a reference to an array in Perl.

A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON are represented by the same codepoints in the Perl string, so no manual decoding is necessary.

A JSON number becomes either an integer, numeric (floating point) or string scalar in perl, depending on its range and any fractional parts. On the Perl level, there is no difference between those as Perl handles all the conversion details, but an integer may take slightly less memory and might represent more values exactly than floating point numbers.

If the number consists of digits only, JSON will try to represent it as an integer value. If that fails, it will try to represent it as a numeric (floating point) value if that is possible without loss of precision. Otherwise it will preserve the number as a string value (in which case you lose roundtripping ability, as the JSON number will be re-encoded toa JSON string).

Numbers containing a fractional or exponential part will always be represented as numeric (floating point) values, possibly at a loss of precision (in which case you might lose perfect roundtripping ability, but the JSON number will still be re-encoded as a JSON number).

If the backend is JSON::PP and allow_bignum is enable, the big integers and the numeric can be optionally converted into the Math::BigInt manpage and the Math::BigFloat manpage objects.

true, false
These JSON atoms become JSON::true and JSON::false, respectively. They are overloaded to act almost exactly like the numbers 1 and 0. You can check wether a scalar is a JSON boolean by using the JSON::is_bool function.

If JSON::true and JSON::false are used as strings or compared as strings, they represent as true and false respectively.

   print JSON::true . "\n";
    => true
   print JSON::true + 1;
    => 1
   ok(JSON::true eq 'true');
   ok(JSON::true eq  '1');
   ok(JSON::true == 1);

JSON will install these missing overloading features to the backend modules.

A JSON null atom becomes undef in Perl.

JSON::null returns unddef.


The mapping from Perl to JSON is slightly more difficult, as Perl is a truly typeless language, so we can only guess which JSON type is meant by a Perl value.

hash references
Perl hash references become JSON objects. As there is no inherent ordering in hash keys (or JSON objects), they will usually be encoded in a pseudo-random order that can change between runs of the same program but stays generally the same within a single run of a program. JSON optionally sort the hash keys (determined by the canonical flag), so the same datastructure will serialise to the same JSON text (given same settings and version of JSON::XS), but this incurs a runtime overhead and is only rarely useful, e.g. when you want to compare some JSON text against another for equality.

In future, the ordered object feature will be added to JSON::PP using tie mechanism.

array references
Perl array references become JSON arrays.

other references
Other unblessed references are generally not allowed and will cause an exception to be thrown, except for references to the integers 0 and 1, which get turned into false and true atoms in JSON. You can also use JSON::false and JSON::true to improve readability.
   to_json [\0,JSON::true]      # yields [false,true]

JSON::true, JSON::false, JSON::null
These special values become JSON true and JSON false values, respectively. You can also use \1 and \0 directly if you want.

JSON::null returns undef.

blessed objects
Blessed objects are not directly representable in JSON. See the allow_blessed and convert_blessed methods on various options on how to deal with this: basically, you can choose between throwing an exception, encoding the reference as if it weren't blessed, or provide your own serialiser method.

With convert_blessed_universally mode, encode converts blessed hash references or blessed array references (contains other blessed references) into JSON members and arrays.

   use JSON -convert_blessed_universally;
   JSON->new->allow_blessed->convert_blessed->encode( $blessed_object );

See to the convert_blessed manpage.

simple scalars
Simple Perl scalars (any scalar that is not a reference) are the most difficult objects to encode: JSON::XS and JSON::PP will encode undefined scalars as JSON null values, scalars that have last been used in a string context before encoding as JSON strings, and anything else as number value:
   # dump as number
   encode_json [2]                      # yields [2]
   encode_json [-3.0e17]                # yields [-3e+17]
   my $value = 5; encode_json [$value]  # yields [5]
   # used as string, so dump as string
   print $value;
   encode_json [$value]                 # yields ["5"]
   # undef becomes null
   encode_json [undef]                  # yields [null]

You can force the type to be a string by stringifying it:

   my $x = 3.1; # some variable containing a number
   "$x";        # stringified
   $x .= "";    # another, more awkward way to stringify
   print $x;    # perl does it for you, too, quite often

You can force the type to be a number by numifying it:

   my $x = "3"; # some variable containing a string
   $x += 0;     # numify it, ensuring it will be dumped as a number
   $x *= 1;     # same thing, the choise is yours.

You can not currently force the type in other, less obscure, ways.

Big Number
If the backend is JSON::PP and allow_bignum is enable, encode converts Math::BigInt objects and Math::BigFloat objects into JSON numbers.


JSON is not a subset of YAML. See to JSON and YAML in the JSON::XS manpage.


When you use JSON, JSON tries to use JSON::XS. If this call failed, it will uses JSON::PP. The required JSON::XS version is 2.2 or later.

The JSON constructor method returns an object inherited from the backend module, and JSON::XS object is a blessed scaler reference while JSON::PP is a blessed hash reference.

So, your program should not depend on the backend module, especially returned objects should not be modified.

 my $json = JSON->new; # XS or PP?
 $json->{stash} = 'this is xs object'; # this code may raise an error!

To check the backend module, there are some methods - backend, is_pp and is_xs.

  JSON->backend; # 'JSON::XS' or 'JSON::PP'
  JSON->backend->is_pp: # 0 or 1
  JSON->backend->is_xs: # 1 or 0
  $json->is_xs; # 1 or 0
  $json->is_pp; # 0 or 1

If you set an enviornment variable PERL_JSON_BACKEND, The calling action will be changed.

Always use JSON::PP

(The default) Use compiled JSON::XS if it is properly compiled & installed, otherwise use JSON::PP.

Always use compiled JSON::XS, die if it isn't properly compiled & installed.

These ideas come from the DBI::PurePerl manpage mechanism.


 use JSON; # always uses JSON::PP

In future, it may be able to specify another module.


Many methods are available with either JSON::XS or JSON::PP and when the backend module is JSON::XS, if any JSON::PP specific (i.e. JSON::XS unspported) method is called, it will warn and be noop.

But If you use JSON passing the optional string -support_by_pp, it makes a part of those unupported methods available. This feature is achieved by using JSON::PP in de/encode.

   use JSON -support_by_pp;
   my $json = new JSON;

At this time, the returned object is a JSON::Backend::XS::Supportable object (re-blessed XS object), and by checking JSON::XS unsupported flags in de/encoding, can support some unsupported methods - loose, allow_bignum, allow_barekey, allow_singlequote, escape_slash, as_nonblessed and indent_length.

When any unsupported methods are not enable, XS de/encode will be used as is. The switch is achieved by changing the symbolic tables.

-support_by_pp is effective only when the backend module is JSON::XS and it makes the de/encoding speed down a bit.



There are big incompatibility between new version (2.00) and old (1.xx). If you use old JSON 1.xx in your code, please check it.

See to Transition ways from 1.xx to 2.xx.

jsonToObj and objToJson are obsoleted.
Non Perl-style name jsonToObj and objToJson are obsoleted (but not yet deleted from the source). If you use these functions in your code, please replace them with from_json and to_json.

Global variables are no longer available.
JSON class variables - $JSON::AUTOCONVERT, $JSON::BareKey, etc... - are not avaliable any longer. Instead, various features can be used through object methods.

Package JSON::Converter and JSON::Parser are deleted.
Now JSON bundles with JSON::PP which can handle JSON more properly than them.

Package JSON::NotString is deleted.
There was JSON::NotString class which represents JSON value true, false, null and numbers. It was deleted and replaced by JSON::Boolean.

JSON::Boolean represents true and false.

JSON::Boolean does not represent null.

JSON::null returns undef.

JSON makes the JSON::XS::Boolean manpage and the JSON::PP::Boolean manpage is-a relation to the JSON::Boolean manpage.

function JSON::Number is obsoleted.
JSON::Number is now needless because JSON::XS and JSON::PP have round-trip integrity.

JSONRPC modules are deleted.
Perl implementation of JSON-RPC protocol - JSONRPC , JSONRPC::Transport::HTTP and Apache::JSONRPC are deleted in this distribution. Instead of them, there is the JSON::RPC manpage which supports JSON-RPC protocol version 1.1.

Transition ways from 1.xx to 2.xx.

You should set suport_by_pp mode firstly, because it is always successful for the below codes even with JSON::XS.

    use JSON -support_by_pp;
Exported jsonToObj (simple)
Exported objToJson (simple)
Exported jsonToObj (advanced)
  $flags = {allow_barekey => 1, allow_singlequote => 1};
  from_json($json_text, $flags);

equivalent to:

  $JSON::BareKey = 1;
  $JSON::QuotApos = 1;
Exported objToJson (advanced)
  $flags = {allow_blessed => 1, allow_barekey => 1};
  to_json($perl_scalar, $flags);

equivalent to:

  $JSON::BareKey = 1;
jsonToObj as object method
objToJson as object method
$JSON::Pretty, $JSON::Indent, $JSON::Delimiter
If indent is enable, that menas $JSON::Pretty flag set. And $JSON::Delimiter was substituted by space_before and space_after. In conclusion:

Equivalent to:


To change indent length, use indent_length.

(Only with JSON::PP, if -support_by_pp is not used.)


(Only with JSON::PP, if -support_by_pp is not used.)

use -convert_blessed_universally. See to the convert_blessed manpage.

(Only with JSON::PP, if -support_by_pp is not used.)

Disable. JSON does not make such a invalid JSON string any longer.


This is the ascii sort.

If you want to use with your own sort routine, check the sort_by method.

(Only with JSON::PP, even if -support_by_pp is used currently.)

  $json->sort_by(sub { $JSON::PP::a <=> $JSON::PP::b })->encode($perl_scalar)

Can't access $a and $b but $JSON::PP::a and $JSON::PP::b.

Needless. JSON backend modules have the round-trip integrity.

Needless because JSON (JSON::XS/JSON::PP) sets the UTF8 flag on properly.
    # With UTF8-flagged strings
    $str = chr(1000); # UTF8-flagged
    $json_text  = $json->utf8(0)->encode($str);
    # true
    $json_text  = $json->utf8(1)->encode($str);
    # false
    $str = '"' . chr(1000) . '"'; # UTF8-flagged
    $perl_scalar  = $json->utf8(0)->decode($str);
    # true
    $perl_scalar  = $json->utf8(1)->decode($str);
    # died because of 'Wide character in subroutine'


Disable. See to MAPPING.

This option was deleted. Instead of it, if a givien blessed object has the TO_JSON method, TO_JSON will be executed with convert_blessed.
  # if need, call allow_blessed

Note that it was toJson in old version, but now not toJson but TO_JSON.


example programs


No test with JSON::PP. If with JSON::XS, See to THREADS in the JSON::XS manpage.


Please report bugs relevant to JSON to <makamaka[at]cpan.org>.


Most of the document is copied and modified from JSON::XS doc.

the JSON::XS manpage, the JSON::PP manpage



Makamaka Hannyaharamitu, <makamaka[at]cpan.org>

JSON::XS was written by Marc Lehmann <schmorp[at]schmorp.de>

The relese of this new version owes to the courtesy of Marc Lehmann.


Copyright 2005-2008 by Makamaka Hannyaharamitu

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

 JSON - JSON encoder/decoder