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Content Security Policy Generator: Build a Safer CSP

Developer Guides By admin 2 min read Updated Oct 21, 2026
Website security and domain configuration guide illustration

Content Security Policy (CSP) is a browser security control delivered through an HTTP response header. It tells the browser which sources are allowed to provide scripts, styles, images and other resources for a page.

Use the CSP Header Builder to assemble a policy and review the directives before deployment.

Why CSP matters

A well-designed policy can reduce the impact of certain injection attacks by preventing the browser from loading or executing resources from unexpected locations. CSP is not a replacement for secure coding, input validation or software updates.

Start with an inventory

Before writing a strict policy, list the external services your site actually uses: analytics, fonts, CDNs, payment scripts, embeds, APIs and media hosts. A policy that ignores required sources can break the site.

How to build a policy

  1. Open the CSP Header Builder.
  2. Define a sensible default-src baseline.
  3. Add specific directives for scripts, styles, images, fonts and connections as needed.
  4. Avoid broad wildcards unless they are truly necessary.
  5. Test the policy before enforcing it site-wide.

Use report-only mode when appropriate

For an existing production site, a report-only deployment can help reveal which resources would be blocked without immediately breaking them. Review violations and tighten the policy iteratively.

If your deployment also minifies HTML containing inline scripts or styles, check the output with the HTML Minifier before applying your policy. Minification can change the exact content used for CSP script or style hashes, so recalculate affected hashes and test the final rendered page.

Common mistakes

  • Allowing every source with broad wildcards.
  • Using unsafe inline script allowances without understanding the risk.
  • Forgetting third-party API or font connections.
  • Deploying a strict policy without testing important forms and checkout flows.

Check related headers

CSP works alongside other response headers. Review the site with the Security Headers Checker and inspect permissions with the Permissions Policy Generator.

Build a draft policy with the UptimeFixer CSP Header Builder, then test it carefully before enforcing it.