Ponytail is a plugin for terminal-based AI coding agents (Claude Code, Codex, Copilot CLI, Gemini CLI, and others) that enforces a seven-step decision ladder—YAGNI, reuse, stdlib, native features, installed dependencies, one-liner, minimum code—before any code is written.

Agentic benchmarks on a real FastAPI repo show 54% fewer lines of code, 20% lower token cost, and 100% safety compared to an unsimplified baseline. The ruleset never cuts validation, error handling, security, or accessibility; reduced output size results from writing only what the task requires.