Pdfgrid is a Python command-line tool and module for adding a regular grid on top of all pages of an existing PDF document. It will mostly be used for measuring individual parts of PDF pages like graphics or paragraph widths. For the time being, only a rectangular grid with major and minor lines is supported, and their colour and line widths can be set individually.
Note: This is an initial release. The API is likely to change and for the time being the grid size is limited to A4, but this will change in future releases.