how to check if a URL is visible from the public Internet

I often test web applications deployed in machines that are local on site (so I access them behind a firewall). Then (after the network people setup some port forwarding scheme) I invite other people to try them out only to be told that they can't seem to be able to see those URLs.

How to test whether a specific URL is visible / reachable from the public Internet?

I am aware of the existence of sites like this but do they test the actual URL (including context, etc. which will involve testing the actual port forwarding) or just accessibility of the node?

Solution 1:

GeoPeeker is a tool for web developers that makes it possible to remotely view a site from different geographic locations. It's great for spotting region-specific content and can be especially helpful when launching a site, as it can be used to ensure that the DNS is propagating properly. GeoPeeker is also pretty handy for troubleshooting CDN and caching issues. The images are rendered using WebKit with a screen width of 1280 pixels.

Solution 2:

Since your Web applications are local they have a local reserved IP addresses (corresponding to their URL) which Reserved Local IP Addresses are, by definition, unreachable outside the local area network...

Ref.: Reserved IP Adresses