What is Content Security Policy and how does it work?
Learn what CSP is, how it prevents XSS attacks, common directives, and best practices for implementing Content Security Policy.
Content Security Policy (CSP) is a security standard that helps prevent XSS attacks by controlling which resources (scripts, styles, images) can be loaded and executed on a web page.
What is Content Security Policy?
A CSP generator creates Content Security Policy headers that specify which sources are allowed to load resources like scripts, styles, images, fonts, and connections. CSP works by whitelisting trusted sources and blocking unauthorized resources. For example, 'script-src 'self'' allows scripts only from the same origin, preventing malicious inline scripts or scripts from untrusted domains. CSP can be delivered via HTTP headers (recommended) or meta tags, and supports report-only mode for testing before enforcement.
In practice, Content Security Policy depends on consistent formatting, predictable URLs, and accurate values so search engines and browsers interpret your intent correctly.
Why Content Security Policy matters for SEO
Content Security Policy matters because it reduces ambiguity about how your pages should be discovered, rendered, or shared. Clear signals help search engines crawl efficiently, improve consistency across URLs, and reduce mistakes that can hurt visibility.
Even for non-SEO tools, the output affects user experience, performance, or accessibility. Those signals influence rankings through engagement and crawlability over time.
How Content Security Policy works
Content Security Policy works by following a small set of rules that browsers and search engines expect. When those rules are consistent, you get predictable behavior across pages and platforms.
- Enable the directives you want to configure
- Add allowed sources for each directive (e.g., 'self', domains, data:)
- Configure report-only mode and report URI if needed
- Generate CSP header in your preferred format
- Add to your server configuration or HTML meta tag
- Test in report-only mode, then enforce
You should use Content Security Policy when
- You want to prevent XSS attacks
- You need to control resource loading
- You're implementing security best practices
- You're required to have CSP for compliance
Examples and use cases
Common scenarios for Content Security Policy include the following. These examples help you decide when to apply it and what to check during implementation.
- Preventing XSS attacks by blocking unauthorized scripts
- Controlling which domains can load resources
- Preventing data exfiltration via connect-src
- Blocking inline scripts/styles (use nonces/hashes instead)
- Complying with security standards and audits
Common mistakes
Most issues come from inconsistent configuration or skipping validation. Avoid the mistakes below to keep results predictable across pages.
- Using 'unsafe-inline' and 'unsafe-eval' unnecessarily
- Not testing in report-only mode first
- Setting overly restrictive policies that break functionality
- Forgetting to include CDN domains in script-src or style-src
- Not using nonces or hashes for inline scripts/styles
FAQs
What's the difference between CSP header and meta tag?
HTTP headers are recommended because they apply to all responses and can't be bypassed. Meta tags are a fallback when you can't set HTTP headers, but they're less secure and only apply to the HTML document. In most cases, the safest approach is to validate your Content Security Policy setup and check results before shipping.
Should I use report-only mode?
Yes, always test in report-only mode first. It reports violations without blocking, helping you identify what needs to be allowed before enforcing the policy. In most cases, the safest approach is to validate your Content Security Policy setup and check results before shipping.
How do I allow inline scripts with CSP?
Avoid 'unsafe-inline' if possible. Instead, use nonces (random tokens) or hashes. Generate a nonce per request, add it to script tags, and include it in your CSP: 'script-src 'nonce-{value}''. In most cases, the safest approach is to validate your Content Security Policy setup and check results before shipping.
What does 'self' mean in CSP?
'self' means the same origin (same protocol, domain, and port). It's a common value that allows resources from your own domain. In most cases, the safest approach is to validate your Content Security Policy setup and check results before shipping.
Do I need Content Security Policy?
You need Content Security Policy when it impacts how your site is crawled, rendered, or shared. If Content Security Policy affects discovery, performance, or compliance, setting it correctly reduces future fixes and makes auditing easier. In most cases, the safest approach is to validate your Content Security Policy setup and check results before shipping.
Does Content Security Policy affect SEO?
Content Security Policy can influence SEO indirectly by improving clarity, crawlability, and user experience. Clear signals help search engines interpret your pages correctly and reduce ambiguity that can lead to weaker rankings. In most cases, the safest approach is to validate your Content Security Policy setup and check results before shipping.
Related resources
These links help you connect related SEO setup tasks and keep your implementation consistent.