Hero opens from CO, Villain defends from BB.
Flop KT3r
Villain donks 50% pot

I ran into those spots quite often in 2€ MTT lately.

I guess it's almost never bluffs.
Could be strong hands.
Could be fragile hands (middle pair, low PPs) testing the waters.

So far I just give up with most of my range here, and only continue with Top Pair +.
But I'm not very happy with it...

Thoughts on how to read those villains ?

That depends alot on the villain and could be anything from 2p to top-/midpairs to pure air. It's rarely that strong, but many villains tend to be sticky once they donk.

I'd definitely continue w most of my decent SD-value on the Flop, i.e. I wouldn't fold Tx or AQ.

I find that small donkbets are typically draws but this sizing is often a weak TP or middle pair just hoping to take it down right there. Even the most fishy of fish have the instinct to check to the raiser when they flop a monster.

If we're talking recs donk betting flop I'd say what Panny1 said; it depends entirely on the villain. You'll see plenty of random donk bets on broadway boards with offsuit ax hands, others will never donk, etc. I would look up the villain and see how often they are punting off stacks/busting early/etc to help range them.

Vs a 50% bet we need to continue with 67% of our range to not be bluffed relentlessly, and rest assured people are "bluffing" at times when they donk bet. I like your idea of continuing tighter overall, but I would not get in the habit of folding good hands to a single 50% bet otf (depending on position/people in pot, spr, reads, etc.)

Ex. kt3 rainbow villian donks 50% do not fold tx, straight draws, etc.

Yeah, I prob tend to overfold I guess here, I'll adjust.
Thanks guys