ponytail — Full Setup Guide

From the seb.ai SAVE drop. How to make your AI coding agent stop over-engineering and write way less code.

What it is

ponytail is a plugin/ruleset you bolt onto your AI coding agent. It makes the agent think like the laziest senior dev in the room: before writing code, it checks if the thing even needs to exist, if the standard library or the browser already does it, or if one line will do. The result is less bloat. Their benchmarks (median of 10 runs across Haiku, Sonnet, and Opus) show 80–94% less code, 3–6x faster, and 47–77% cheaper than a no-skill agent.

  • Repo: https://github.com/DietrichGebert/ponytail
  • Built by: Dietrich Gebert
  • License: MIT (free for commercial use)
  • Stars: ~13.6k (check the live page, it moves)
  • Works with 13 agents: Claude Code, Codex, GitHub Copilot, Cursor, Gemini/Antigravity, OpenCode, Pi, Windsurf, Cline, Kiro, Aider, and more.

One thing to check first

The Claude Code and Codex plugins run two tiny Node.js hooks, so make sure node is on your PATH. If it isn't, the skills still work, the always-on activation just stays quiet instead of erroring.

Install — pick your agent

Claude Code (recommended)

/plugin marketplace add DietrichGebert/ponytail
/plugin install ponytail@ponytail

Codex

codex plugin marketplace add DietrichGebert/ponytail
codex

Then open /plugins, select the Ponytail marketplace, install Ponytail. Open /hooks, review and trust its two lifecycle hooks, and start a new thread. Restarting the Codex desktop app picks it up too.

GitHub Copilot CLI

copilot plugin marketplace add DietrichGebert/ponytail
copilot plugin install ponytail@ponytail

Gemini CLI / Antigravity CLI

gemini extensions install https://github.com/DietrichGebert/ponytail
# or, on Antigravity:
agy plugin install https://github.com/DietrichGebert/ponytail

Pi agent harness

pi install git:github.com/DietrichGebert/ponytail

Cursor, Windsurf, Cline, Kiro, Copilot (editor), Aider

These don't take plugins, so you just copy the matching rules file from the repo into your project: .cursor/rules/, .windsurf/rules/, .clinerules/, .github/copilot-instructions.md, AGENTS.md, or .kiro/steering/. This gives you the always-on rules (no slash commands).

How to use it

Once installed it's active every session. You don't have to do anything, but you can control the intensity and run reviews with these commands:

  • /ponytail [lite | full | ultra | off] — set how aggressive it is, or turn it off. No argument shows the current level. Default is full.
  • /ponytail-review — reviews your current diff for over-engineering and hands back a delete-list.
  • /ponytail-audit — audits the whole repo, not just the diff.
  • /ponytail-debt — collects the shortcuts you deferred (marked with ponytail: comments) into a ledger so "later" doesn't become "never".
  • /ponytail-help — quick reference.

Set a default level for every new session with the PONYTAIL_DEFAULT_MODE env var (lite/full/ultra/off), or a defaultMode field in ~/.config/ponytail/config.json.

What it actually does (the before/after)

Ask for a date picker. A normal agent installs a library, writes a wrapper component, adds a stylesheet, and starts a debate about timezones. With ponytail you get:

<!-- ponytail: browser has one -->
<input type="date">

Every shortcut it takes is marked with a ponytail: comment naming the upgrade path, so nothing is hidden.

Tips

  • Start on full (the default). Bump to ultra when a codebase has personally wronged you. Use lite if it's trimming too hard.
  • Run /ponytail-review before you commit. It's the fastest way to see the bloat you'd have shipped.
  • It's "lazy, not negligent" by design: security, input validation, data-loss handling, and accessibility are never cut.
  • Want to verify the numbers yourself? Reproduce the benchmark: npx promptfoo eval -c benchmarks/promptfooconfig.yaml

That's it. Go let your agent ship less.

— Seb / @seb.ai