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A Content-Security-Policy (CSP) header does not blank a Next.js page by itself. It makes the browser refuse specific resources that the policy does not allow. If one of those refused resources is a script the page needs to run, the HTML may render but never become interactive, and on some pages the visible result looks like an empty screen. The fix starts with the browser’s own violation messages, not with loosening the policy.
This guide shows how to confirm that CSP is the cause, identify the exact blocked resource and directive, correct the policy without weakening it blindly, and rule out hydration errors and edge or CDN changes that can produce the same symptom.
Why a CSP header can stop a Next.js page from working
CSP is enforced by the browser. Each directive lists the sources the browser may load a resource from or run code from. When a page requests something outside those sources, the browser blocks it and logs a violation. For a Next.js page, the blocked item is often a script that the framework needs during hydration, the step where React attaches event handlers to server-rendered HTML. Without that script, the markup can be present while buttons, navigation, and data loading do nothing.
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Confirm CSP is the cause
Work through these steps in order. Each one either proves the cause or rules it out.
- Reproduce with developer tools open. Open the affected URL in a fresh tab with DevTools open (F12 or Ctrl+Shift+I on Windows and Linux, Cmd+Option+I on macOS). Go to the Console tab and reload. Look for messages that begin with a CSP violation, and record the blocked URL or inline script, the directive named in the message, and the page URL.
- Inspect the document response headers. Go to the Network tab, select the HTML document request (the first entry for the page URL), and open the Headers section. Record every
Content-Security-Policyand everyContent-Security-Policy-Report-Onlyheader. Check the HTML<head>for a<meta http-equiv="Content-Security-Policy">element as well. - Identify all layers that add a policy. A CDN, reverse proxy, load balancer, or hosting platform can add its own header alongside the one in your Next.js configuration. Multiple policies all apply, and each one can only further restrict what the page may do. A script is allowed only if every applicable policy permits it.
- Match the violation to code the page needs. A violation is not automatically the reason for the blank screen. Check whether the blocked resource is one of your application scripts, a framework script, a stylesheet, or an analytics or third-party request that the page can survive without.
- Check for a hydration error. If the violations are unrelated to the page’s critical scripts, or there are none, go to the hydration section below before editing any policy.
Read the violation and map it to a directive
The directive named in the console message tells you which part of the policy to change. The most common ones in this situation are listed below.
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| Directive named in the violation | What it controls | What to check first |
|---|---|---|
script-src |
Sources for JavaScript, including inline scripts and eval-style execution, when no more specific directive applies |
Whether the blocked script is external or inline, and whether it has a permitted nonce or hash |
script-src-elem |
Sources for <script> elements specifically |
The origin of the external script file, or whether an inline script element lacks a valid nonce |
style-src |
Sources for stylesheets and inline styles | Whether a CSS-in-JS library or inline style injection is being blocked |
connect-src |
Sources for network requests made from script, such as fetch, XHR, and WebSocket connections |
Whether a data API, auth endpoint, or analytics endpoint is blocked |
The MDN script-src reference describes how JavaScript sources are restricted and how inline script is treated. Use it to confirm why a given inline script is blocked before you decide how to authorize it.
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There are two implementation choices for a Next.js app, and they differ in how the policy is delivered and what must stay in sync.
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| Approach | How it is delivered | Best fit | Main cost |
|---|---|---|---|
| Static policy | A fixed Content-Security-Policy value set through the headers() option in next.config.js for matching paths |
Applications that do not need per-response nonces and whose script sources are known in advance | Any inline script must be authorized another way, and the rule set must be kept narrow by hand |
| Nonce-based policy | A fresh nonce generated per request, placed in the response policy and on each rendered script element | Applications that need inline scripts from the framework or application while still avoiding 'unsafe-inline' |
Requires dynamic rendering for the affected pages and a per-response match between header and markup |
Static policy for pages without nonces
Next.js documents setting response headers through next.config.js for paths you specify. Keep the match deliberate. A document-level CSP belongs on HTML documents, and the Next.js Pages Router CSP guide recommends excluding static assets and prefetch requests that do not need the policy. Applying one broad rule to every request can add headers to files where they serve no purpose and make failures harder to read.
Nonce-based policy
The Next.js 14 Pages Router CSP guide shows the pattern. A nonce is generated in Middleware for each request, the CSP is set on the request that is passed to the framework and on the response, and the nonce is exposed to a Server Component or to next/script. The guide states the rule plainly: “Every time a page is viewed, a fresh nonce should be generated.” That requirement also means the pages involved must be dynamically rendered, because a statically generated page cannot receive a new nonce for each view.
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When you use this approach, check these points:
- The nonce in the
Content-Security-Policyresponse header matches thenonceattribute on the rendered script elements for the same response. - The nonce is generated per request, not once at build time or per deployment.
- The value is a random, unpredictable string. Next.js reports an error for nonces containing
<,>, or&, and recommends a randomly generated UUID. Do not build nonces from user input or other untrusted data. - Any CDN or page cache is not serving an HTML response whose nonce no longer matches the header sent with it. A nonce is only useful for the single response it was generated for, so cached markup with an old nonce will be blocked.
The next/script component forwards additional DOM attributes such as nonce. Its loading strategies (beforeInteractive, afterInteractive, and lazyOnload) change when a script runs, not whether CSP allows it. The worker strategy is experimental and is not supported with the App Router. Changing a strategy will not fix a script that the policy blocks.
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Why a broad allowlist is the wrong first move
Adding 'unsafe-inline', 'unsafe-eval', https:, or a wildcard source can make the blank page go away, but it reduces the protection the header was added to provide. Use these only after you have identified the blocked resource and confirmed that a narrower change cannot work. The correct change is usually one of the following: add the specific origin of a required external script, add a correctly applied nonce or hash for a specific inline script, or remove a conflicting policy from one of the layers.
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Roll out the policy safely with report-only mode
Use Content-Security-Policy-Report-Only while you evaluate a policy. The browser reports violations without blocking the code, so you can see every resource the policy would stop before users see a blank page. The MDN CSP header reference documents this mode.
- Send the candidate policy as
Content-Security-Policy-Report-Onlyand leave any enforced header out of the test. - Load the main routes, then exercise the interactions that depend on JavaScript: navigation between pages, forms, client-side data loading, and any login or checkout flow.
- Review the console for violations on each route and note any blocked script that the page needs.
- Correct the policy for each legitimate blocked resource, using the narrowest source or a correctly matched nonce.
- Repeat until a full pass produces no violations for required resources, then switch the header name from
Content-Security-Policy-Report-OnlytoContent-Security-Policy. - After enforcement, load the same routes once more and check that the page becomes interactive.
Report-only results show what was blocked during your test session. They do not prove that every route and state will work under enforcement, so keep the test list broad.
When CSP is not the cause
If the console shows no violation for a required resource, or the page still fails after the policy is corrected, check the rendering path. The Next.js hydration error guide lists several causes of hydration errors, and each can produce a page that looks blank or stops responding:
- Server and client render different output, for example because a value differs between the two environments.
- Browser-only APIs such as
windoworlocalStorageare read during rendering. - Time-dependent values, such as the current time or random numbers, change between the server render and the client render.
- Browser extensions modify the DOM before React hydrates it.
- The CSS-in-JS setup does not produce the same styles on the server and client.
- An edge or CDN layer modifies the HTML before it reaches the browser.
The edge or CDN case deserves a direct check. Compare the HTML your origin server returns with the HTML the browser receives. If a proxy inserts, removes, or rewrites script tags, or injects its own policy, the markup and the header can stop matching even when your application code is correct.
Version and documentation notes
The Pages Router CSP guide linked above is a versioned page. Its path includes /docs/14/, and it was last updated September 1, 2023. Its version history recommends Next.js 13.4.20 or later for proper nonce handling. Check the current documentation for the Next.js version your application actually installs before copying any example, because routing and middleware APIs have changed across releases. The current Next.js Scripts guide was updated February 27, 2026, and is the reference for next/script behavior in newer versions.
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