How to block Cloudflare Browser Run
Operated by Cloudflare. Renders web pages in headless browsers for Cloudflare customers. Used for browser automation (screenshots, PDF generation, content extraction, etc.) and for AI agents to interact with the web. Used by Cloudflare customers via Workers bindings and REST API. Does not include the /crawl endpoint, which has a separate bot identity (Cloudflare Crawler - Signed Agent).
How it identifies itself
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.107 Safari/537.36 (compatible; +https://developers.cloudflare.com/security-center/)
robots.txt
What the agent asks to be told. It obeys this or it does not — nothing enforces it.
User-agent: cloudflare-browser-rendering Disallow: /
nginx
In the server block, then reload.
# In the server block. 403 rather than 444: a closed connection tells the
# operator nothing, and an agent that gets a status code can log it.
if ($http_user_agent ~* "(cloudflare-browser-rendering|Cloudflare Browser Rendering)") {
return 403;
}
Apache
In .htaccess or the vhost.
BrowserMatchNoCase "cloudflare-browser-rendering" bad_bot
BrowserMatchNoCase "Cloudflare Browser Rendering" bad_bot
<RequireAll>
Require all granted
Require not env bad_bot
</RequireAll>
Cloudflare
Security → WAF → Custom rules.
# Security → WAF → Custom rules, action: Block (http.user_agent contains "cloudflare-browser-rendering") or (http.user_agent contains "Cloudflare Browser Rendering")
WordPress
A child theme's functions.php, or a small plugin.
// functions.php of a child theme, or a small plugin. Runs before WordPress
// builds the page, so a blocked agent costs one PHP process and no queries.
add_action('init', function () {
$agent = $_SERVER['HTTP_USER_AGENT'] ?? '';
foreach (['cloudflare-browser-rendering', 'Cloudflare Browser Rendering'] as $needle) {
if (stripos($agent, $needle) !== false) {
status_header(403);
exit('Blocked: Cloudflare Browser Run');
}
}
});
robots.txt is a request. The rules below it are the wall.
Cloudflare Browser Run publishes a token, so the directive above will work for as long as it keeps honouring it — and nothing except its own good manners makes it. The server rules match on a header the requester sets, which stops the agent that says who it is and not the one that copies somebody else's name. Botscope verifies identity against DNS and published address ranges, records which check decided each request, and shows you the ones that lied.