Basehold.it is an external stylesheet which creates a baseline grid overlay to help you adjust vertical rhythm.

All you need is just to insert this code into head section of your HTML file:

<link rel="stylesheet" href="http://basehold.it/24">

You can change the baseline height to any value by adjusting the number at the end of url. Plus you can change color to anything you want by adding Hex values, RGB values, or RGBA after the height in the url.

Image of text with vertical rhythm grid under it

Demo
More info — basehold.it