Nope, it's not. But it does require a bit of investment. There's several methods you can use. My brackish crab tank currently is in a 14 gal, which is the same footprint as a 10 gal but taller. I have it filled up about 10 gals full. The crabs share the tank with bumblebee gobies. There is a floating island with sturdy plants creating a ladder. There is a mongrove root style peice of decor that sticks out of the water. They actually also use the intank filter as a third space for them to air out, and enjoy a meal off the filter pad
Another style set up you can do is a simple sand slope. For your crabs I'm going to recommend atleast a 10 gal tank, so you have enough space to provide both adequate water and land areas. You could do a slope of sand,or sand mixed with gravel, up one side of the tank and partially fill the other half of the tank.
For filtration, because this will be a partially filled tank, you will need an in-tank filter. This can be a power filter or a sponge filter. If you already have an air pump, a sponge filter would be a great affordable solution for this tank. You'll also need a heater. And a tight fitting lid. You want no holes in the lid large enough for a crab to escape through. They are great escape artists.
This will need to be a brackish water tank. You will need marine salt, make sure it's not aquarium salt. Also a hydrometer to measure the salinity level. You don't use much marine salt to create brackish water, so that investment will last you quite a while.