The showkeys package modifies the \label, \ref, \pageref, \cite and \bibitem commands so that the ‘internal’ key is printed, without affecting the appearance of the rest of the text, so far as is possible (the keys typically appear in the margin).

The package is part of the tools bundle in the LaTeX required distribution.

The author is David Carlisle. The package is Copyright © 1992-1997,2006,2007 David Carlisle.