ponytail

Apply a YAGNI decision ladder that checks whether code needs to exist, whether it already exists in the codebase, and whether the stdlib covers it before writing anything new. This Skill enforces that ladder on every coding response by default.

Grep every caller of the function you plan to edit before making changes, then place one guard in the shared function all callers route through. Patching only the reported path leaves sibling callers broken.

Yes, three intensity levels are available: lite suggests lazier alternatives while building what was asked, full enforces the ladder as the default, and ultra prioritizes deletion and challenges requirements. Switch with /ponytail lite, full, or ultra.

Never simplify away input validation at trust boundaries, error handling that prevents data loss, security measures, accessibility basics, or anything explicitly requested. Hardware-related code also needs calibration knobs that a minimal model cannot anticipate.

Non-trivial logic such as branches, loops, parsers, or money and security paths requires one runnable check, like an assert-based self-check or a single small test file. Trivial one-liners need no test since YAGNI applies to tests too.