What are the valid URLs that can be used in a query variable?

Question

What are the valid characters that can be used in a URL request variable?

I ask because I would like to create a GUID of the smallest string length using the largest character set if they can be passed as a URL query variable (www.StackOverflow.com?query=guiddaf09834fasnv)

Edit

If you want to encode the UUID / GUID or any other information presented in an array of bytes into a string convenient for the URL, you can use this method in the Apache Commons Code Library :

Base64.encodeBase64URLSafeString(byte[])

Answer 1

, RFC.

. , URL-.

"2.2. URL-"

... alphanumerics, "$ -_. +! * '()," , , URL-.