Since Chrome 72, requests to localhost (127.0.0.1) or link-local IP do not go through a proxy by default.

Implicit bypass rules:

Requests to certain hosts will not be sent through a proxy, and will instead be sent directly.

We call these the implicit bypass rules. The implicit bypass rules match URLs whose host portion is either a localhost name or a link-local IP literal. Essentially it matches:

  localhost
  *.localhost
  [::1]
  127.0.0.1/8
  169.254/16
  [FE80::]/10

The complete rules are slightly more complicated. For instance on Windows we will also recognize loopback, and there is special casing of localhost6 and localhost6.localdomain6 in Chrome's localhost matching.

Workaround

The easiest workaround is to simply access your remote localhost via a globally resolvable hostname, e.g.

local.test.cab
*.local.test.cab

But if your remote localhost is configured to allow connections from hostname localhost only, then you need to configure chrome to ignore the implicit bypass rule.

Override Chrome Implicit Bypass Rule via cmd/shell

To override the implicit bypass rule, you can run chrome with the following command line flag on Windows:

"%LocalAppData%\Google\Chrome SxS\Application\chrome.exe" --proxy-bypass-list="<-loopback>"

or on Linux:

google-chrome --proxy-bypass-list="<-loopback>"
chromium --proxy-bypass-list="<-loopback>"

Override Chrome Implicit Bypass Rule via SwitchyOmega

If using SwitchyOmega Chrome extension, proxy of Chrome is controlled by it, so we need to add <-loopback> into Bypass List of the profile configured in the extension.

SwithyOmega

Fix ERR_CONNECTION_REFUSED

This site can’t be reached. localhost refused to connect. ERR_CONNECTION_REFUSED

When you see this error, it may be caused by your request not going to the proxy server. Please recheck you've configured chrome to override implicit bypass rules correctly.

Fix ERR_EMPTY_RESPONSE

If you've configured chrome to ignore the implicit bypass rules, but still can't get access to the website hosted on your proxy server via localhost:

This page isn't working. localhost didn't send any data. ERR_EMPTY_RESPONSE

You need to check whether you've input the correct port number.

And to check whether there is an entry for localhost in /etc/hosts file on the proxy server:

127.0.0.1   localhost

If not, add the above line to the file, and try reloading the page.

Alternatively, simply access it via IP address 127.0.0.1

Fix ERR_SSL_PROTOCOL_ERROR

This site can’t provide a secure connection. localhost sent an invalid response. ERR_SSL_PROTOCOL_ERROR

If you see the SSL error, you're accessing an HTTP site via HTTPS.

This may be caused by either incorrectly entering https:// instead of http://, or HSTS policy set to the localhost domain.

You can query and clear the HSTS status in chrome via <chrome://net-internals/#hsts> Query Expect-CT domain and Delete domain security policies.

Chrome net-internals HSTS

If things are still not working…

Check the log of your proxy server. Please note that some proxy servers are configured to disallow connections to localhost, so you may have to configure the proxy sever itself.

References