PHP Manual


(PHP 4, PHP 5)

uniqid — Generate a unique ID


string uniqid ([ string $prefix [, bool $more_entropy ]] )

Gets a prefixed unique identifier based on the current time in microseconds.



Can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond.

With an empty prefix , the returned string will be 13 characters long. If more_entropy is TRUE, it will be 23 characters.


If set to TRUE, uniqid() will add additional entropy (using the combined linear congruential generator) at the end of the return value, which should make the results more unique.

Return Values

Returns the unique identifier, as a string.


If you need a unique identifier or token and you intend to give out that token to the user via the network (i.e. session cookies), it is recommended that you use something along these lines:

This will create a 32 character identifier (a 128 bit hex number) that is extremely difficult to predict.

Example#1 uniqid() Example

// no prefix
// works only in PHP 5 and later versions
$token md5(uniqid());

// better, difficult to guess
$better_token md5(uniqid(rand(), true));


Version Description
5.0.0 The prefix parameter was made optional.
4.3.1 The limit of 114 characters long for prefix was raised.

PHP Manual