Agent skill · writing content · dietrichgebert
ponytail-review
Review a diff for over-engineering. Finds what to delete: reinvented stdlib, needless deps, speculative abstractions. One line per finding.
Why this skill is useful
Adds a structured approach to identifying and documenting over-engineering in code diffs, which the AI wouldn't reliably generate on its own.
What it needs
About 1k tokens when loaded. Last updated 2026-07-15. 97,533 stars on the source repository.
What this skill does
Review diffs for unnecessary complexity. One line per finding: location, what to cut, what replaces it. The diff's best outcome is getting shorter. Format L<line>: <tag> <what>. <replacement>., or <file>:L<line>: ... for multi-file diffs. Tags: delete: dead code, unused flexibility, speculative feature. Replacement: nothing. stdlib: hand-rolled thing the standard library ships. Name the function. native: dependency or code doing what the platform already does. Name the feature. yagni: abstraction with one implementation, config nobody sets, layer with one caller. shrink: same logic, fewer lines. Show the shorter form. Examples ❌ "This EmailValidator class might be more complex than necessary, have you considered whether all these validation rules are needed at this stage?" ✅ L12-38: stdlib: 27-line validator class. "@" in email, 1 line, real validation is the confirmation mail. ✅ L4: native: moment.js imported for one format call. Intl.DateTimeFormat, 0 deps. ✅ repo.py:L88: yagni: AbstractRepository with one implementation. Inline it until a second one exists. ✅ L52-71: delete: retry wrapper around an idempotent local call. Nothing replaces it. ✅ L30-44: shrink: manual loop builds dict. dict(zip(keys, values)), 1 line. Scoring End with the only metric that matters: net: -<N> lines possible. If there is nothing to cut, say Lean already. Ship. and stop. Boundaries Scope: over-engineering and complexity only. Correctness bugs, security holes, and performance are explicitly out of scope. Route them to a normal review pass, not this one. A single smoke test or assert-based self-check is the ponytail minimum, not bloat, never flag it for deletion. Does not apply the fixes, only lists them. "stop ponytail-review" or "normal mode": revert to verbose review style.
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills dietrichgebert/ponytail-review