Rinse the crabs under cold water
Fill a large pot with 1 to 2 inches of water
Add salt to the water if desired
Place a steaming rack or basket in the pot
Bring the water to a boil
Put the crabs on the rack or basket
Cover the pot tightly
Steam until the crabs turn bright red and are heated through
Cook small crabs for about 10 to 15 minutes
Cook large crabs for about 15 to 20 minutes
Remove the crabs with tongs
Serve immediately