Headers

import { Code } from "/components"; import { Render } from "/components";

Custom headers

The default response headers served on static asset responses can be overridden, removed, or added to, by creating a plain text file called _headers without a file extension, in the static asset directory of your project. This file will not itself be served as a static asset, but will instead be parsed by Cloudflare Pages and its rules will be applied to static asset responses.

<Render product="workers" file="headers_redirects_directory-pages" params={{ filename: "_headers" }} />

Headers defined in the _headers file override what Cloudflare ordinarily sends.

:::caution

Custom headers defined in the _headers file are not applied to responses generated by Pages Functions, even if the request URL matches a rule defined in _headers. If you use a server-side rendered (SSR) framework, or Pages Functions (with either a folder of functions/ or an "advanced mode" _worker.js), you will likely need to attach any custom headers you wish to apply directly within that Pages Functions code.

:::

Attach a header

Header rules are defined in multi-line blocks. The first line of a block is the URL or URL pattern where the rule's headers should be applied. On the next line, an indented list of header names and header values must be written:

[url]
  [name]: [value]

Using absolute URLs is supported, though be aware that absolute URLs must begin with https and specifying a port is not supported. _headers rules ignore the incoming request's port and protocol when matching against an incoming request. For example, a rule like https://example.com/path would match against requests to other://example.com:1234/path.

You can define as many [name]: [value] pairs as you require on subsequent lines. For example:

<Code lang="txt" code={# This is a comment\n/secure/page\n\tX-Frame-Options: DENY\n\tX-Content-Type-Options: nosniff\n\tReferrer-Policy: no-referrer\n\n/static/*\n\tAccess-Control-Allow-Origin: *\n\tX-Robots-Tag: nosnippet\n\nhttps://myproject.pages.dev/*\n\tX-Robots-Tag: noindex} />

An incoming request which matches multiple rules' URL patterns will inherit all rules' headers. Using the previous _headers file, the following requests will have the following headers applied:

You may define up to 100 header rules. Each line in the _headers file has a 2,000 character limit. The entire line, including spacing, header name, and value, counts towards this limit.

If a header is applied twice in the _headers file, the values are joined with a comma separator.

Detach a header

You may wish to remove a default header or a header which has been added by a more pervasive rule. This can be done by prepending the header name with an exclamation mark and space (! ).

/*
  Content-Security-Policy: default-src 'self';

/*.jpg
  ! Content-Security-Policy

Match a path

The same URL matching features that _redirects offers is also available to the _headers file. Note, however, that redirects are applied before headers, so when a request matches both a redirect and a header, the redirect takes priority.

Splats

When matching, a splat pattern — signified by an asterisk (*) — will greedily match all characters. You may only include a single splat in the URL.

The matched value can be referenced within the header value as the :splat placeholder.

Placeholders

<Render product="workers" file="headers_redirects_placeholders" params={{ filetype: "header" }} />

/movies/:title
  x-movie-name: You are watching ":title"

Examples

Cross-Origin Resource Sharing (CORS)

To enable other domains to fetch every static asset from your Pages project, the following can be added to the _headers file:

/*
  Access-Control-Allow-Origin: *

This applies the Access-Control-Allow-Origin header to any incoming URL. To be more restrictive, you can define a URL pattern that applies to a {'*.pages.dev'} subdomain, which then only allows access from its staging branch's subdomain:

<Code lang="txt" code={https://:project.pages.dev/*\n\tAccess-Control-Allow-Origin: https://staging.:project.pages.dev/} />

Prevent your workers.dev URLs showing in search results

Google and other search engines often support the X-Robots-Tag header to instruct its crawlers how your website should be indexed.

For example, to prevent your *.pages.dev and *.*.pages.dev URLs from being indexed, add the following to your _headers file:

<Code lang="txt" code={https://:project.pages.dev/*\n\tX-Robots-Tag: noindex\n\nhttps://:version.:project.pages.dev/*\n\tX-Robots-Tag: noindex} />

Configure custom browser cache behavior

If you have a folder of fingerprinted assets (assets which have a hash in their filename), you can configure more aggressive caching behavior in the browser to improve performance for repeat visitors:

/static/*
  Cache-Control: public, max-age=31556952, immutable

Harden security for an application

:::caution

If you are server-side rendering (SSR) or using Pages Functions to generate responses in any other way and wish to attach security headers, the headers should be sent from the Pages Functions' Response instead of using a _headers file. For example, if you have an API endpoint and want to allow cross-origin requests, you should ensure that your Worker code attaches CORS headers to its responses, including to OPTIONS requests.

:::

You can prevent click-jacking by informing browsers not to embed your application inside another (for example, with an <iframe>) with a X-Frame-Options header.

X-Content-Type-Options: nosniff prevents browsers from interpreting a response as any other content-type than what is defined with the Content-Type header.

Referrer-Policy allows you to customize how much information visitors give about where they are coming from when they navigate away from your page.

Browser features can be disabled to varying degrees with the Permissions-Policy header (recently renamed from Feature-Policy).

If you need fine-grained control over your application's content, the Content-Security-Policy header allows you to configure a number of security settings, including similar controls to the X-Frame-Options header.

/app/*
  X-Frame-Options: DENY
  X-Content-Type-Options: nosniff
  Referrer-Policy: no-referrer
  Permissions-Policy: document-domain=()
  Content-Security-Policy: script-src 'self'; frame-ancestors 'none';