So, your snake laid eggs. How to make sure they are viable ? The only method for this is candling. It is a routine check performed for chicken eggs on farms. It is a simple and non-intrusive procedure.
 

 
  What do you need for candling ? There are commercial candlers sold on the market, but it can be also easily done using a simple MagLite flashlite.
 

 
Make sure that the room where you do your candling is dark. Place the light against an egg - a viable (live, fertile) egg will show red veins inside. A dead egg will not show them.

What precoutions are there to take ? First, the light shouldn't be held agains the eggs for too long. A couple seconds is enough for the examination. Lightbulbs get hot and this heat could damage the embryo. Having a piece of cardboard wrapped around the flashlight will keep the source away from the egg. Still, you shouldn't expose the eggs to such bright light for too long - this too can affect the embryo and kill it. Some species are very sensitive to this, for example the chandro family. The last thing would be to always make sure that the eggs will stay in the same position at all times. They should never be flipped over. The eggs position is easy to maintain when they are all stuck together in a mass. When having them seperate, it is always a good practice to mark the top of the eggs with a pencil.
 

 
Another shot at candling - the blood vessels are clearly visible. This egg is fertile and if incubated under the right conditions the snake should hatch after about 60 days.