Getting "net::ERR_BLOCKED_BY_CLIENT" error on some AJAX calls

Question 1

AdBlockers usually have some rules, i.e. they match the URIs against some type of expression (sometimes they also match the DOM against expressions, not that this matters in this case).

Having rules and expressions that just operate on a tiny bit of text (the URI) is prone to create some false-positives...

Besides instructing your users to disable their extensions (at least on your site) you can also get the extension and test which of the rules/expressions blocked your stuff, provided the extension provides enough details about that. Once you identified the culprit, you can either try to avoid triggering the rule by using different URIs, report the rule as incorrect or overly-broad to the team that created it, or both. Check the docs for a particular add-on on how to do that.

For example, AdBlock Plus has a Blockable items view that shows all blocked items on a page and the rules that triggered the block. And those items also including XHR requests.

Blockable items

Question 2

If your URL contains words such as "advert", "ad", "doubleclick", "click", or something similar…

For example:

GET googleads.g.doubleclick.net/pagead/id
static.doubleclick.net/instream/ad_status.js

…Then ad-blocker will block it.

Question 3

I've discovered that if the filename has 300 in it, AdBlock blocks the page and throws a ERR_BLOCKED_BY_CLIENT error.

Question 4

I was facing same issue, I was using Brave Browser, disabling protection against site on which I was facing issue worked

Question 5

Add PrivacyBadger to the list of potential causes

Question 6

I find a case is if your url contains the key word banner, it will blocked too.

Question 7

I had sentry calls failing with this and disabling brave ads shield on Brave browser did solve the issue for me.

Question 8

As it has been explained here, beside of multiple extensions that perform ad or script blocking you may aware that this may happen by file names as below:

Particularly in the AdBlock Plus the character string "-300x600" is causing the Failed to Load Resource ERR_BLOCKED_BY_CLIENT problem.

As shown in the picture, some of the images were blocked because of the '-300x600' pattern in their name, that particular text pattern matches an expression list pattern in the AdBlock Plus.

Question 9

If there are any ad blockers (Brave browser use default blocker), turn it off. This worked for me

Question 10

In my case, it is not the adblocker but Bitdefender anti tracker. Disable it then you all fine.

Question 11

Just switching the order of some URL query params fixed the issue for me (so apparently the uBlock Origin adblocking rules are not very robust).

Question 12

In my case it was a Chrome extension and Firefox add-on by Avira called "Avira Browser Safety". I had problems with version 1.7.4. In my specific case I wanted to login to a website called gliffy.com for making diagrams, but after logging in I got an blank page. If you use F12 (console) in Chrome you can see all these ERR_BLOCKED_BY_CLIENT (and other) errors.

Question 13

This error can also happen if you run chrome in headless mode (for example with Puppeteer or Ferrum) with a white list of URLs and the request doesn't match the list.

Question 14

Opera Blocker and others check all files/urls in Network. Then compares to the list. It is EasyPrivacy and EasyList. If your file/url in this, your will be ban. Good luck.

So... I find FilterLists for all addBlockers!

Question 15

Thanks for the answers! They led me to a solution:

I cheated this by using a third party server that wrapped my request.
Check it out:
https://codetabs.com/cors-proxy/cors-proxy.html

GET "https://api.codetabs.com/v1/proxy?quest=your_blocked_url"

Of course, it is better to wrap it with your own server.