I'm not sure why an external tool won't be helpful.

In QGIS, for example, it is pretty straightforward to calculate the feature envelopes. There is also a coordinate panel at the bottom of the window that shows the map coordinates as you move the mouse. This can be used to check the coordinates of features you are interested in without having to calculate their specific geometries.

If you are comfortable using R then the sf library has tools to access features (geometries), and the st_bbox function will give you the feature envelope.