TCP port testing links for convenience

The http://portquiz.net/ site provides a valuable service for free: the server listens an almost all TCP ports and replies with a simple HTML if the request was successful. You can use this to test whether something between a client and this server filters access to certain ports.

If you're testing from a browser, keep in mind that they block access to certain ports as well.
Chromium's list: https://chromium.googlesource.com/chromium/src.git/+/refs/heads/master/net/base/port_util.cc
Firefox's list: https://hg.mozilla.org/mozilla-central/file/tip/netwerk/base/nsIOService.cpp

The latter is an extension of the Chromium list by adding the 4160 and 6679 ports.

If you want to do some testing from a browser, here's a list of links that you just have to click.

Note that portquiz.net applies rate limiting on the source IP addresses so clicking through all of these in a single session won't work.

This is a list of some well-known ports (from https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers) that are not on the browser restricted list.