A webpage is not always broken because of a large mistake. Small details can produce exactly this problem: debugging: csp blocks an inline script. This guide shows you what to look for, a concrete fix, and how to check that it worked.
The Idea in Plain English
An inline script is rejected when the active CSP does not permit it. Prefer a trusted external script or a correctly generated nonce.
HTML supplies the structure; JavaScript supplies the behavior described here. If you remove the script, check what remains usable for visitors.
A Working Example
The first part shows a problem. The second part shows a safer or more accurate version. Compare them before reading the explanation.
<!-- Problem -->
<meta http-equiv="Content-Security-Policy" content="script-src 'self'">
<script>alert("Hello")</script>
<!-- Corrected example -->
<meta http-equiv="Content-Security-Policy" content="script-src 'self'">
<script src="/js/app.js" defer></script>What Each Part Does
- The script element can load code or hold data; the type attribute tells the browser how to treat its contents.
- The meta element supplies machine-readable settings; its name or charset decides which setting.
- content supplies the value of a meta declaration.
- src points to the asset the browser should load.
Before the fix, the browser can behave incorrectly or report a warning. After the change, test the exact failure rather than assuming the page is fixed.
Try It Yourself
Check the CSP violation in Console and verify that the external script is same-origin.
Common Beginner Mistakes
- Check the underlying cause before changing unrelated tags.
- Copying the code without checking whether its linked files or endpoints exist; sample addresses and file paths need real resources.
- Choosing a tag only because its default appearance looks right, without checking whether it describes the content correctly.
Key Takeaways
- An inline script is rejected when the active CSP does not permit it. Prefer a trusted external script or a correctly generated nonce.
- Before the fix, the browser can behave incorrectly or report a warning. After the change, test the exact failure rather than assuming the page is fixed.
- Test the markup in a browser, and check accessibility and real-world behavior where relevant.