Ruby core API that lets code subscribe to runtime events (method calls, returns, line execution, raises, etc.). Used by RBS to implement its runtime type checking. An audience member at wroclove.rb 2024 asked whether Sorbet's runtime checks are implemented on top of TracePoint and whether Sorbet's performance overhead stems from TracePoint's slowness; Erwin Kroon did not know the answer and deferred to John Hawthorne.