Highlight Refontification is a tool for that visualizes the font-lock refontification process, written by Anders Lindgren.

This package provides a minor mode that visualizes how font-lock refontifies a buffer. This is useful when developing or debugging font-lock keywords, especially for keywords that span multiple lines.

The background of the buffer is painted in a rainbow of colors, where each band in the rainbow represent a region of the buffer that has been refontified. When the buffer is modified, the rainbow is updated.

Getting the package

The Highlight Refontification package is located on Github.