Is it a bad practice to use a GET parameter (in URL) with no value?

Question

I'm in a little argument with my boss about URLs using GET parameters without value. E.g.

http://www.example.com/?logout

I see this kind of link fairly often on the web, but of course, this doesn't mean it's a good thing. He fears that this is not standard and could lead to unexpected errors, so he'd rather like me to use something like:

http://www.example.com/?logout=yes

In my experience, I've never encountered any problem using empty parameters, and they sometimes make more sense to me (like in this case, where ?logout=no wouldn't make any sense, so the value of "logout" is irrelevant and I would only test for the presence of the parameter server-side, not for its value). (It also looks cleaner.)

However I can't find confirmation that this kind of usage is actually valid and therefore really can't cause any problem ever.

Do you have any link about this?

Answer 1

RFC 2396, "Uniform Resource Identifiers (URI): Generic Syntax", §3.4, "Query Component" is the authoritative source of information on the query string, and states:

The query component is a string of information to be interpreted by the resource.

[...]

Within a query component, the characters ";", "/", "?", ":", "@", "&", "=", "+", ",", and "$" are reserved.

RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1", §3.2.2, "http URL", does not redefine this.

In short, the query string you give ("logout") is perfectly valid.