In the process of porting a unity web-player app to WebGL I'm running into some issues: There are runtime errors and the mangled stacktraces make it very hard to understand what is going on. In the player settings I have enabled Soft Null exceptions and have set Scripting Define Symbols to "DEMANGLE_SUPPORT=1;ASSERTIONS=2". Yet I get warnings like these in my browser: a problem occurred in builtin C++ name demangling; build with -s DEMANGLE_SUPPORT=1 to link in libcxxabi demangling Build with ASSERTIONS=2 for more info. I'm building via BuildPipeline.BuildPlayer with BuildOptions.AllowDebugging | BuildOptions.Development These are the sort of stacktraces I get: http://i.imgur.com/ip2yHAR.png What is the process of enabling demangling and getting proper stacktraces? Is it possible to hook into the webGL build process at a certain stage? It is very hard to construct a minimal failure case if it is hard to figure out where the error lies.