Sometimes we ask others to do something for us, and they do not reject our request, but do not promise to do it either; they give us a maybe-answer such as "I don't promise, but will try to do my best" or "If I got some spare time". Is there any word/phrase for such kind of answer to requests?
a noncommittal response or answer TFD
Refusing commitment to a particular opinion or course of action; not revealing what one feels or thinks:
tentative response ?
- Not fully worked out, concluded, or agreed on; provisional.
American Heritage Dictionary
"I don't promise, but will try to do my best"
"If I got some spare time"
Both of these sound subject to change so I'd say tentative or provisional.