Hi im new on cesium development and i am looking a tool like google earth ruler, my question is: is something like this in cesium or i have to make it ?
This is not something included with Cesium, so you would have to make your own widget. You can use an EllipsoidGeodesic to find the distance along the ellipsoid surface between two points.
You might consider starting with the one in TerriaJS, which is a library that uses Cesium and Leaflet under the hood. The source file that implements distance (and also area) measurement is here:
Live demo here:
(click the icon on the right under the zoom in/out buttons)
More about TerriaJS here:
Thank you! its just i looking for!!!