Ponytail
A ruleset that makes your coding agent write the least code that works
About Ponytail
Ponytail is a ruleset you install into a coding agent to stop it over-building. Its core is a ladder the agent has to climb before it writes anything: does this need to exist at all, is it already in this codebase, does the standard library do it, does a native platform feature cover it, does an already-installed dependency solve it, can it be one line, and only then, the minimum code that works. The agent stops at the first rung that holds. The example the project leads with is a date picker: the browser already has a native date input, so 404 lines became 23.
It is worth being clear about what this is, because it is not software in the usual sense. There is no runtime and no model. It is a set of rules plus a handful of slash commands, distributed through plugin marketplaces and instruction files, and its entire effect comes from changing what the agent decides to do. That is also its honest limitation: you could write the ladder into your own agent instructions and capture a good part of the value in an afternoon. What the project adds is the commands, the intensity settings, and the fact that someone has already tuned the wording across a dozen different agents. It is MIT licensed, and the safety rules are explicitly excluded from the trimming: validation, error handling, security and accessibility are never the thing that gets simplified away.
On Claude Code it is two lines, add the marketplace and install the plugin. Codex, Copilot CLI, Gemini CLI and Pi each have their own one-line install. For agents with no plugin system, including Cursor, Windsurf, Cline, VS Code, Aider, Kiro, Zed, JetBrains and Sourcegraph Amp, you copy the rule files into wherever that agent reads its instructions from. Once installed you drive it from chat. One command sets the intensity or turns it off entirely, another reads the current diff specifically for over-engineering, another sweeps the whole repository for accumulated bloat, another collects the shortcuts you deferred into a single ledger, and another prints the benchmark scoreboard. Node.js on PATH is required for the lifecycle hooks on Claude Code and Codex.
- •The Ladder - Seven rungs, from does this need to exist to build the minimum, applied before any code gets written
- •Three Intensities - lite names the lazier alternative and leaves the choice to you, full enforces the ladder, ultra ships the one-liner and argues with the requirement in the same breath
- •Diff Review - A command that reads the current diff looking for over-engineering rather than for bugs
- •Repository Audit - A whole-repository sweep for bloat that accumulated before you installed it
- •Debt Ledger - Deferred shortcuts collected into one place instead of being lost in chat history
- •Broad Agent Support - Plugin installs for more than a dozen agents and instruction-file fallbacks for the rest
- •Safety Carve-Out - Validation, error handling, security and accessibility are excluded from what gets trimmed
Anyone whose agent answers a small request by installing a library, adding a configuration layer and writing documentation for it. It fits reviewers and tech leads as much as the person doing the prompting, since running the review command over a diff is a quick way to find the abstraction nobody asked for. It suits established codebases better than greenfield work, because half the ladder is about reusing what is already there. Two cautions. The benchmark numbers on the landing page, 54 percent less code and 22 percent fewer tokens among them, are the author's own measurements: medians across 12 feature tasks on a single FastAPI and React repository using one model, and nobody has replicated them independently. The project itself notes that terse reasoning models may see no cost or latency gain at all. And if you like an agent that scaffolds generously and fills in structure before you have asked for it, this will argue with you all day.
Pricing
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Free and MIT licensed. There is no paid tier and no pricing page. Installs as a plugin on Claude Code, Codex, Copilot CLI, Gemini CLI and Pi, or as rule files for agents without a plugin system.
From the vendor pricing page, 2026-10-08
