Lets say I discovered a consistent setup for a hard and inconsistent trick. ethically speaking, is it fine to keep it a secret until I use it in a run?
should I reveal and explain it immediately? what's the consensus about this? I know speedrunning is a group effort, so is it fair to hold back info for a while?
You can do whatever you want. But generally speaking, speedrun communities (and possibly even speedrunning as a whole) are built on collaboration, not just competition. Whatever information people find regarding a particular speedrun should be shared, and should be public knowledge to the speedrunning community. Keeping strats or skips a secret only hinders the community from collectively improving their times.
So IMO, it's not really fair.
I say speedrunning is a community effort and if new tech is discovered, it should be shared and explained. It boils down to who you are as a person.
Really as long as it doesn't stay private (especially if you make it clear you know something the rest of the community doesn't) for too long no one will really care, it's not like there aren't plenty of people doing offline routing / practice that have tricks / trick ideas that aren't public yet especially for less popular games and categories.
What @TransparantBlue is saying. As long as you're not hoarding the strat for all time to come, saving it for 2 days until you can set a new record, it's fine.
And for the love of batman, don't do this in a competition with money on the line ;)