What a content security policy is
A content security policy, often abbreviated CSP, is a security feature that lets a website tell the browser which sources of content are allowed to be loaded and run on its pages. By declaring these rules, a site can restrict where scripts, images, and other content may come from. The browser then enforces the policy, blocking content that does not meet the site's declared rules.
Controlling allowed sources
The core idea of a content security policy is to define a set of trusted sources for different kinds of content. Instead of allowing a page to load anything from anywhere, the site specifies what is permitted. The browser honors these restrictions, so content from sources outside the policy is not loaded or executed. This gives the site control over what runs on its pages.
Mitigating cross-site scripting
One of the main benefits of a content security policy is helping to mitigate cross-site scripting attacks. Since XSS relies on getting malicious scripts to run on a page, a policy that restricts which scripts are allowed can block injected scripts from executing. While not a complete solution on its own, CSP adds a valuable layer of defense against this common class of attack.
How the browser enforces it
A content security policy works because the browser enforces it on the site's behalf. The site communicates its policy, and the browser applies the rules as it loads the page, refusing to load or run anything that violates them. This browser-side enforcement means the protection applies consistently whenever the page is viewed, strengthening the site's defenses against unauthorized content.
A defense-in-depth measure
A content security policy is best understood as part of a layered approach to web security, often called defense in depth. It does not replace careful handling of input and output, but it adds another barrier that can stop certain attacks even if other defenses fail. Combining CSP with other good practices makes a site more resilient against a range of threats.
Why it matters
A content security policy is an important tool in web security. Understanding what it is - a way for a site to tell the browser which content sources are allowed - clarifies how sites reduce the risk of attacks like cross-site scripting. For anyone interested in web security, it is a valuable concept to understand.
Related on Skillo
See also: What is cross-site scripting (XSS)? Explained, What is the same-origin policy? Explained.
Sources
Published date reflects the original event date (2026-05-12). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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