Visit in winter Nov to February.
If you just like to enjoy beauty of Kerala monsoon June July is also good, but you cannot involve in any outdoor activities
There is no right time, whenever you visit there,make it your best time and there are various things to do in Kerala
backwaters, boat rides, coffee farms, hill stations, richest temple in the world,sunset and sunrise points, delicious foods
Kerala is one of the best place to visit. Between March and October is the best time to visit Kerala. The climate would be cool and pleasant where can enjoy the sightseeing It is the place which offers mind-blowing backwaters, beaches , nature spots and many more.
https://www.indianeagle.com/traveldiary/beaches-in-kerala/
September to march is the best time to visit Kerala to enjoy the charming beauty in a pleasant weather. If you are travelling to kerala,you shouldn;t miss these things in kerala.
Cruise the backwaters
Visit a tea plantation
Go hiking in Munnar
Beaches on the Arabian Sea
Periyar Jungle
Fort Kochi
June to August's rainy season. move Jan winter perfect time are these two. I prefer winter, rains can be harsh sometimes. It's been for the last three years. there is a lot to explain. Kerala can't be described in this box. I am from Kerala. And have travelled every part of the states.