Mago author here.

The online playground is running a very old version (~0.20.0 from months ago, which did not even have a static analyzer) and gives a poor impression of the current tool. That's on me to fix or take down.

The issue you saw with built-in classes like `RuntimeException` was absolutely a bug in those early alpha versions, but it has been fixed for a long time now. The analyzer has matured a lot since then.

The current beta is stable enough to be the sole static analysis tool for a couple of extremely well-typed projects:

- https://github.com/azjezz/psl/ - https://github.com/carthage-software/cel-php

I'd definitely encourage trying the latest release locally to get a real feel for it. Thanks again for the write-up!