Sorting in a GET request param doesn't alter the server's state. It only changes the data representation, not the underlying resources.
This fits "safe" method def (RFC 9110) https://www.rfc-editor.org/rfc/rfc9110.html#safe.methods
But I agree sorting feels like it’s doing “something”… which is where I got stuck thinking about this.
But are you saying that the client view state (example of the sorted data) should not be handled by the server via GET?
If that’s what your are thinking, I’d like to learn more on this rule.
But changing the "default" sort order of a resource (either by physically shuffling the rows on disk or by setting some server-side global variable) would not.
I think it's the difference between making a sorted copy of a list (while leaving the original list untouched) and inline-sorting the list.
Same applies to filtering.
Even storing the processed results in a cache does not validate idempotency, because from a client's POV, the behavior of the next request would be the same, whether the server calculates the result fresh or pulls it from the cache.
(Edit: Realized, I mixed up "idempotent" and "safe" methods there. I was talking about "safe" methods - but those are what applies to GET requests and what can be represented by a hyperlink)
(Nothing stops you in practice from ignoring that requirement, but it can lead to ugly surprises, such as a crawler triggering a mass deletion because it crawled the /delete links)
Not if you want to be pedantic. At least, if you want to follow the rules, GET requests should never change visible state on the server.
So the interactivity would be limited to searching/filtering existing content, but you wouldn't be able to add new content.
For that, you'd need POST requests, i.e. buttons.