Internet Explorer has a limit of 4096 rules per CSS file. When this limit is exceeded, the browser silently ignores the excess rules, often leading to unexplained page rendering problems.

CssRuleCount is a command-line .NET tool which uses the System.Windows.Forms.WebBrowser class to parse the specified CSS file and exits with error code 1 if the rule count exceeds the limit. Since the WebBrowser class is backed by Internet Explorer's rendering engine, the rules are counted just as Internet Explorer would count them. No GUI windows are created; CssRuleCount is suitable for integrating into an automated build pipeline.