Explain This Diff

The reviewer doesn't know what you know. A diff without narrative forces them to reconstruct intent from code, which is slow and error-prone. This skill produces the narrative.

When to use

• Opening a non-trivial PR — generates the description.
• Handing a stale PR to a fresh reviewer mid-week.
• Annotating a long-running feature branch for someone joining the project.
• Code archaeology — explaining a historical commit to current you.

When NOT to use

• Trivial diffs (typo, lint fix) — title is enough.
• Generated code changes (lockfile, generated proto) — note them and skip the body.

The narrative shape

For any diff, produce: