Desktop browsers let you inspect network traffic via a developer console. For mobile devices you can install software like Charles proxy onto your local computer and proxy HTTP and HTTPS traffic from your phone through that computer and inspect there.
Is there a web app that does what Charles proxy does? If not, why? Would a web proxy that allows developers to see network requests sent by their phones or any other device that doesn't have a developer console be useful?
Would people pay for this?
http://people.apache.org/~pmuellr/weinre-docs/latest/Home.ht...
http://jsconsole.com/remote-debugging.html
The examples might show debugging on a local network, but it is certainly possible (and fairly easy) to do it across the internet.
I would advise against running it on a site with even a moderate amount of traffic.
This might also have some features that you are looking for: http://newrelic.com/real-user-monitoring They're not free though.
The steps to use these tools are generally: insert a single javascript file (with a unique identifier) into the pages you want to debug, the view their custom console for errors. It's very simple and very useful.