ERR_BLOCKED_BY_CLIENT: An extension blocked the request

The browser itself refused to send the request because an extension — usually an ad or tracker blocker — matched it against a block list. The server was never contacted.

Short answer

The browser itself refused to send the request because an extension — usually an ad or tracker blocker — matched it against a block list. The server was never contacted.

What ERR_BLOCKED_BY_CLIENT means

This is entirely client-side. The request never left the browser. It commonly hits analytics, ad and tracking endpoints, and occasionally first-party paths whose names resemble them.

Causes and fixes, most likely first

1. An ad blocker or privacy extension matched the URL. Test in a private window with extensions disabled to confirm, then allowlist the domain if the request is legitimate.
2. A first-party path contains a word matched by a filter list (ads, analytics, track). Rename the path or serve the script from a first-party route that does not match common filter patterns.

How to stop it happening again

• Avoid filter-bait words in first-party asset paths.
• Never make critical functionality depend on a request that filter lists commonly block.

Check your own domain

An external probe fetches the URL with no extensions in the way, proving the resource is served correctly and the block is local.

Frequently asked questions

Does ERR_BLOCKED_BY_CLIENT affect SEO?

No. Crawlers do not run ad blockers. It affects real users with extensions, and only for the specific blocked requests.