name: measure-before-optimizing description: Verify a bottleneck exists before touching performance. Use before any caching, memoization, query rewrite, algorithm swap, or "this seems slow" change; when a spec sets a performance target or Core Web Vitals threshold; when a user reports slowness; or when a PR bundles a performance claim with no before/after number. Skip for a fix where the bottleneck is already obvious from the code itself (e.g. an accidental O(n²) on a hot path). metadata: version: "1.0.0"

Measure First

The discipline is the same everywhere — measure, pinpoint, fix, re-measure, and skip optimizing what the data says doesn't matter — but how it's applied is calibrated per model. Pick the file for the model actually running:

Read the file matching the model actually running before applying this skill.

Running a model not listed above (an older generation, a different model family entirely)? sonnet-5.md carries the fullest general-purpose version of the underlying procedure — read that one rather than skipping this skill.