Whether you're a seasoned designer or an absolute beginner, you sometimes will want to see if there are problems in your model, or if there are quirks in the gcode from the slicer. Here are some useful online tools that can help:
Will It 3D Print? Catch likely problems in your design: http://willit3dprint.com
STL manifold errors? Fix your STL files online: http://cloud.netfabb.com/
Review the Gcode to see what will get printed: http://gcode.ws
