Content Security Policy (CSP) Guide: Prevent XSS Without Breaking UX

A Content Security Policy (CSP) is an HTTP header that allows site operators to restrict the resources (such as JavaScript, CSS, Images) that a browser is allowed to load for a given page.

Why CSP saves lives (and code)

Cross-Site Scripting (XSS) is one of the most prevalent vulnerabilities. If a hacker injects a malicious <script> tag into your forum, the browser normally executes it. But with a strict CSP, the browser will refuse to run any script that isn't explicitly whitelisted!

A Strong Baseline CSP

Content-Security-Policy: default-src 'self'; script-src 'self' https://analytics.google.com; style-src 'self' 'unsafe-inline';

This rule says: Load everything from my own domain only. Allow scripts from Google Analytics, and allow inline styles. Everything else? Block it.

The Deployment Trick

Do not enforce CSP blindly. Use the Content-Security-Policy-Report-Only header first. It won't block anything, but it will send reports of what would have been blocked to a logging server.

Building the syntax manually is tedious. Use our client-side CSP Generator to visually assemble your policy, then test your live site with the Security Headers Check to confirm the implementation.

Rollout strategy that avoids breakage

Inventory all script and style sources first, then deploy report-only mode for at least one release cycle. Promote to enforcement only after violations are understood and legitimate dependencies are whitelisted.

Practical KPI targets

Track blocked script attempts, XSS incident trends, and policy drift between environments. Security headers work best when measured like product features.