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. Reproduce it yourself.}

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">

More survivors in examples/.

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. Reproduce it yourself: npx promptfoo eval -c benchmarks/promptfooconfig.yaml. Method and raw numbers: benchmarks/. Production-grade tasks, where an unconstrained agent bloats far more, are written up in benchmarks/results/.

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:

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.

Pi agent harness

pi install git:github.com/DietrichGebert/ponytail

OpenCode

Run OpenCode from a checkout of this repo (the plugin reuses its hooks/ and skills/), and add to opencode.json:

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

Injects the ruleset every turn at the active level; adds /ponytail and /ponytail-review. OpenCode also auto-loads this repo's AGENTS.md, so the rules hold even without the plugin. The plugin adds the lite/full/ultra/off levels.

That was it. He'd be proud. He won't say it.

Active every session. /ponytail-review finds what to delete in your diff. /ponytail ultra exists for when the codebase has wronged you personally. /ponytail-help explains the rest.

In Codex, invoke the skills as @ponytail, @ponytail-review, and @ponytail-help. Startup and mode-change text shows the current mode.

Cursor, Windsurf, Cline, Copilot, Aider, Kiro: copy the matching rules file from this repo (.cursor/rules/, .windsurf/rules/, .clinerules/, .github/copilot-instructions.md, AGENTS.md, .kiro/steering/).

Kiro: copy .kiro/steering/ponytail.md to ~/.kiro/steering/ (global) or .kiro/steering/ in your project.

Which files map to which agent: Agent portability.

Development

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

node scripts/check-rule-copies.js

FAQ

Does it need a config file? No.

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.