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Ponytail (GitHub Repo)

Ponytail (GitHub Repo)

Tech aiagentsdevops GitHub
Ponytail is a ruleset and agent plugin that forces AI coding assistants to prefer native features and standard libraries over bloated, generated dependencies.
What: Ponytail injects a 'less is more' philosophy into popular AI coding tools like Claude Code, GitHub Copilot, and Cursor. It forces agents to check for YAGNI (You Ain't Gonna Need It), standard library alternatives, and native platform features before writing new code.
Why it matters: AI coding agents frequently over-engineer by default, often defaulting to heavy NPM dependencies instead of native browser or standard library functions. This project addresses the 'hallucinated dependency' and bloat problem by imposing strict design constraints at the system prompt level.
Takeaway: Install the Ponytail plugin in your IDE or CLI agent to automatically audit your AI-generated code for unnecessary dependencies and over-engineering.
Deep dive
  • Forces agents to prioritize standard libraries and native APIs over external dependencies.
  • Implements a hierarchy: 1. Delete unnecessary code, 2. Use standard lib, 3. Use platform features, 4. Use existing dependencies, 5. Write only the minimum needed.
  • Supports major tools: Claude Code, Copilot, Cursor, Windsurf, Cline, and Gemini CLI.
  • Includes audit commands: /ponytail-review, /ponytail-audit, and /ponytail-debt to manage technical debt.
  • Reduces code bloat by 80–94% and cost by 47–77% in benchmark tests.
  • Operates as a plugin or simple rule-file injection for agents that support custom instructions.
Decoder
  • YAGNI: "You Ain't Gonna Need It"; a software development principle where you do not add functionality until it is deemed absolutely necessary.
  • Agent: An AI system configured to take autonomous actions in a development environment, such as writing files, executing tests, or installing packages.
  • Promptfoo: A CLI tool for testing, evaluating, and benchmarking the performance and quality of LLM prompts.
Original article

Ponytail

He says nothing. He writes one line. It works.

80-94% less code · 3-6× faster · 47-77% cheaper
Median of 10 runs across Haiku, Sonnet, and Opus.

You know him. Long ponytail. Oval glasses. Has been at the company longer than the version control. You show him fifty lines; he looks at them, says nothing, and replaces them with one.

Ponytail puts him inside your AI agent.

Before / after

You ask for a date picker. Your agent installs flatpickr, writes a wrapper component, adds a stylesheet, and starts a discussion about timezones.

With ponytail:

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

Numbers

Five everyday tasks (email validator, debounce, CSV sum, countdown timer, rate limiter), three models, three arms: no skill, the caveman skill, and ponytail. Ten runs per cell, median reported.

80-94% less code, 47-77% less cost, and 3-6× faster than a no-skill agent, on every model. Every shortcut ponytail takes is marked in the code with a ponytail: comment naming its upgrade path.

How it works

Before writing code, the agent stops at the first rung that holds:

1. Does this need to exist?   → no: skip it (YAGNI)
2. Stdlib does it?            → use it
3. Native platform feature?   → use it
4. Installed dependency?      → use it
5. One line?                  → one line
6. Only then: the minimum that works

Lazy, not negligent: trust-boundary validation, data-loss handling, security, and accessibility are never on the chopping block.

Install

The most effort ponytail will ever ask of you:

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

Claude Code

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

Codex

codex plugin marketplace add DietrichGebert/ponytail
codex

Open /plugins, select the Ponytail marketplace, and install Ponytail. Then open /hooks, review and trust its two lifecycle hooks, and start a new thread.

GitHub Copilot CLI

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

In an interactive Copilot CLI session, use the slash equivalents:

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

Pi agent harness

pi install git:github.com/DietrichGebert/ponytail

OpenCode

Run OpenCode from a checkout of this repo, and add to opencode.json:

{ "plugin": ["./.opencode/plugins/ponytail.mjs"] }

Gemini CLI

gemini extensions install https://github.com/DietrichGebert/ponytail

Antigravity CLI

agy plugin install https://github.com/DietrichGebert/ponytail

Commands

Command What it does
/ponytail [lite | full | ultra | off] Set the intensity, or turn it off. No argument reports the current level.
/ponytail-review Review the current diff for over-engineering, hands back a delete-list.
/ponytail-audit Audit the whole repo for over-engineering, not just the diff.
/ponytail-debt Harvest the ponytail: shortcuts you've deferred into a ledger, so "later" doesn't become "never".
/ponytail-help Quick reference for the commands above.

Development

When changing the compact rule text, keep the agent copies aligned:

node scripts/check-rule-copies.js
npm test

FAQ

Does it need a config file? No. An optional ~/.config/ponytail/config.json or PONYTAIL_DEFAULT_MODE env var can set the default level, but nothing is required.

What if I really need the 120-line cache class? You don't. Insist anyway and he'll build it. Slowly. Correctly. While looking at you.

Does it scale? The code you never wrote scales infinitely. Zero bugs, zero CVEs, 100% uptime since forever.

Why "ponytail"? You know exactly why.

License

MIT. The shortest license that works.

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