Why is the comma URL encoded?

Question

When debugging in ASP.NET MVC, I don't see a difference between:

http://mysite.com?q=hi,bye 

and

http://mysite.com?q=hi%2Cbye 

The querystring param "q" always has a value of "hi,bye".

So why is the comma encoded?

I want to do something like this https://stackoverflow.com/a/752109/173957.

I have this form:

<form method="GET" action="/Search">      <input type="hidden" name="q" value="hi,bye"/>      <input type="submit" value="ok"/> </form> 

How can I prevent this value from being encoded?

Answer 1

The URI spec, RFC 3986, specifies that URI path components not contain unencoded reserved characters and comma is one of the reserved characters. For sub-delims such as the comma, leaving it unencoded risks the character being treated as separator syntax in the URI scheme. Percent-encoding it guarantees the character will be passed through as data.

Answer 2

I found this list of characters that do not require URL encoding: http://web.archive.org/web/20131212154213/http://urldecoderonline.com/url-allowed-characters.htm

Update
Since the original link broke, I used archive.org to get the following text from the page from on December 2013

List of allowed URL characters

Unreserved - May be encoded but it is not necessary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 - _ . ~ 

Reserved - Have to be encoded sometimes

! * ' ( ) ; : @ & = + $ , / ? % # [ ]