XSS game : Warning: You are entering the XSS game area.
XSS Filter Evasion Cheat Sheet - OWASP : This article is focused on providing application security testing professionals with a guide to assist in Cross Site Scripting testing.
HTML Purifier : HTML Purifier is a standards-compliant HTML filter library written in PHP. HTML Purifier will not only remove all malicious code (better known as XSS)...
mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
Grype : A vulnerability scanner for container images and filesystems.
The following rules are intended to prevent all XSS in your application. While these rules do not allow absolute freedom in putting untrusted data into an HTML document, they should cover the vast majority of common use cases.