It could be a black racer if it appears to have blueish scales it is skinny. A black pine snake if it has some brown or white splotches. It can be a eastern indigo snake but is a large snake and has a brown or reddish color underneath head. You probably saw a Black Racer, but all are nonpoisonous.
What kind of snake has a yellow underneath is black with yellow dots?
Black snake in louisiana
I saw a black snake with yellow underneath and yellow spots nearer to tail.about 24 to 30 inches long, very slender. What kind of snake is this? It was spotted in wooded area around a lake.