I enabled tracing and it created a file trace.231189926.xt.
Which tools can open it without crashing on big files?
I used xdebug.trace_format=2 to make it save it as HTML, but my browser crashes if I try to load the file into it, since it is > 4 GB in size.
Is there a specialised tool for .xt files?
As far as I know, there is no tool to read the .xt files mode 0 (human readable) or mode 2 (HTML).
For mode 1 (computer readable), there is a script that runs some rudimentary analysis on the trace files in Xdebug's contrib/ directory. It is called tracefile analyser.
With the latest Xdebug, 3.3, there are two new modes (3 and 4), which generate flame graphs. These can be read by many tools. And you can read up on that in this blog post.