I catch dungeness and red rock crab (Oregon coast). I googled ‘how to clean a crab’. I’m still not sure whether to boil it alive or clean it first. Are there health risks boiling it whole?
Assuming it’s alive when the crab goes in the pot, there are no meaningful risks to you. The crab is not so fortunate.
I’ve never heard of cleaning a crab before it’s cooked.
Agreed.
Make sure you use a very large pot, one that exceeds the reach of the crab from longest leg to longest leg (don’t ask me how I know this).
Bring water to a rolling boil. Store your live crab on ice to slow it down a bit while you wait for the water to boil. Salt your water to taste like the sea.
Plunge the crab with firm resolve head first into the water. This will kill it in an instant.
Once cooked, simply pull off the carapace shell and clean out the innards.
Eat the rest of the soft bits.
Yum.
The debate isn’t over.
https://www.google.com/amp/s/www.ifish.net/board/showthread.php%3Ft=263390&=1
Maybe not for you. 
Interesting, though.
Do you think cleaning it first changes the taste?
I’d clean a soft-shell before cooking, or have the fishmonger do it.
I can’t answer that question, since I’ve only ever cooked them alive and whole. I’ve never found cleaning them after to taint the meat in any way – and I’m not a fan of the tomalley (either crab or lobster), so I clean them very well.
Once I remove the carapace, I break them in half, pull off the lungs and rinse the inside thoroughly. That’s all there is to it, except for all that shell-cracking.
Like Alpha Twit, I’ve never heard of cleaning them before cooking. But as you know, Dungeness are hard shell crabs, not soft shell.
I clean the (Dungeness) crabs before cooking them. For one thing, there’s no use cooking stuff I’m not going to eat. For another, you can get more crabs in the pot.
How I do it:
[ul][li]Lay the crab on its back;[/li][li]Lay a meat cleaver (or bolo knife, or machete, or whatever) along the crab’s longitudinal axis;[/li][li]Give the blade a sharp whack with a rubber mallet.[/ul][/li]This bisects the crab’s brain and kills it instantly. Once dead:
[ul][li]Grasp the legs and wrench them from the body;[/li][li]‘Flick’ the legs to remove some organs’[/li][li]Remove the gills and any remaining organs;[/li]Boil the crab halves in salted water for 11 minutes.[/ul]
My wife used to be a fishmonger. They never boiled their crabs alive, deeming it more efficient and ethical to kill them by sticking a skewer up their bum before boiling.
Always pick the flesh after cooking though, not before.
I wouldn’t clean a Dungeness before cooking, as I want that good tomalley. Blue crab, on the other hand, benefits mightily by cleaning before cooking, as their innards are reminiscent of, um, diaper contents.