URL-parameters input seems inconsistent

Question

I have review multiple instructions on URL-parameters which all suggest 2 approaches:

Parameters can follow / forward slashes or be specified by parameter name and then by parameter value. so either:

1)  http://numbersapi.com/42

or

2)  http://numbersapi.com/random?min=10&max=20

For the second one, I provide parameter name and then parameter value by using the?. I also provide multiple parameters using ampersand.

Now I have see the request below which works fine but does not fit into the rules above:

 http://numbersapi.com/42?json

I understand that the requests sets 42 as a parameter but why is the ? not followed by the parameter name and just by the value. Also the ? seems to be used as an ampersand?

Answer 1

From Wikipedia:

Every HTTP URL conforms to the syntax of a generic URI. The URI generic syntax consists of a hierarchical sequence of five components:

URI = scheme:[//authority]path[?query][#fragment]

where the authority component divides into three subcomponents:

authority = [userinfo@]host[:port]

This is represented in a syntax diagram as:

As you can see, the ? ends the path part of the URL and starts the query part.

The query part is usually a &-separated string of name=value pairs, but it doesn't have to be, so json is a valid value for the query part.

Or, as the Wikipedia articles says it:

• An optional query component preceded by a question mark (?), containing a query string of non-hierarchical data. Its syntax is not well defined, but by convention is most often a sequence of attribute–value pairs separated by a delimiter.

It is also fairly common for request processors to treat a name=value pair that is missing the = sign, as if the it was name=.

E.g. if you're writing Servlet code and call servletRequest.getParameter("json"), it would return an empty string ("") for that last URL in the question.