Diagnosing Bugs walks an agent through a rigorous discipline for handling hard bugs and performance regressions. It prevents premature guessing by enforcing a structured sequence: building a tight feedback loop, reproducing and minimising the issue, generating ranked hypotheses, instrumenting probes, applying a fix with regression tests, and cleaning up instrumentation. Reach for this skill when the user needs a systematic, multi-phase debugging process for broken, throwing, failing, or slow code.