I noticed that the documentation for LinkSnooper says that it is "obsolete". I don't have any experience with this tool, but I thought it looked interesting after seeing results it was able to provide in some of the answers here on Mathematica SE.

Are there better facilities for this kind of analysis present in Mathematica or available as add-ons or external software?

The online documentation may indicate that the online documentation is obsolete; the LinkSnooper itself is still alive and kicking! Just go to the Documentation Center and look at the guide page of JLink:

JLink/guide/CallingTheWolframLanguageFromJava


scroll down to "LinkSnooper" and there you have it.

I use LinkSnooper quite often, because it is one of the rare tools that helps you investigating in

• how dynamic stuff is working
• how the internal debugger works
• how autocompletion of your functions is achieved

In fact, I use it so regularly, that I even started to write a better version of it that supports basic highlighting and better copy&paste support of the packets, because I find myself often enough in the situation where I want to test expressions in a notebook. I gave it the name Pink Roselon which is an anagram of LinkSnooper:

I haven't worked on it for some time since it seems incredibly hard creating a list-view of highlighted text that works super-smoothly even for a large amount of data.

Another way of inspecting front-end to kernel communication is to write your own traffic logger directly inside Mathematica. If you want to know how this can be done, I strongly recommend reading the article MathLink Mode by David Wagner and the reference therein.

FileNames["LinkSnooper.java", {\$InstallationDirectory}, Infinity]