Development & infrastructureDietrich GebertOpen source
Ponytail
Decision matrix
Ponytail app decision matrix
Overview
Ponytail is a free, MIT-licensed skill/ruleset that pushes AI coding agents toward the smallest solution that works: question whether code is needed at all, check for an existing library or platform feature before writing new code, and default to fewer lines. Pick it when your agent tends to over-build. It installs into 14+ agents including Claude Code, Copilot, Gemini, Cursor and Windsurf, with adjustable intensity from "lite" to "ultra".
Other good fits
A quick audit pass (/ponytail-review) to find and flag unnecessary complexity in existing code.
+ Pros
Read pros
Ponytail is a ruleset for AI coding agents built around one idea: "the best code is the code never written." Before writing new code, it pushes the agent through a decision hierarchy: does this need code at all, does an existing standard library or platform feature already handle it, does an already-installed dependency cover it, and only then write something new, and write the smallest version that works. It supports 14+ agents including Claude Code, GitHub Copilot, Gemini, Cursor and Windsurf, and offers intensity levels: "lite" suggests alternatives, "full" enforces the decision hierarchy, and "ultra" pushes for extreme minimalism.
Pick it when…
Your coding agent tends to produce more code, more abstraction, or more dependencies than the task actually needs.
You want a quick, repeatable way to audit existing code for unnecessary complexity.
You're working in one of the 14+ agents it supports and want this as a default behaviour, not a one-off prompt.
− Cons
Read cons
A default toward minimalism isn't universally correct: some problems genuinely need the abstraction, dependency, or flexibility that a "smallest possible solution" approach would resist adding. Use judgment about which projects benefit from the push toward less code and which need room to grow; a library meant to be extended by others is a different case than a one-off script. It only works within its 14+ supported agents, so confirm compatibility with your specific tool before relying on it. The project's own agentic benchmark (12 feature tasks on a FastAPI/React repo, mean across runs) reports roughly 46% less code, 22% fewer tokens, 20% lower cost and 27% faster completion versus no skill at all, with full safety compliance; that's the project's own reported measurement, not an independent test, so treat it as a promising signal rather than a guarantee for your specific codebase.
Pick something else when…
You're not using a supported agent. Check its current list of 14+ supported agents before assuming compatibility.
Your project actively needs more structure and abstraction, not less. A framework or library meant for extension by others may need patterns that look like "unnecessary" complexity to a minimalism-first rule.
You want a broader code-quality review, not specifically an over-engineering check. A general code-review tool covers correctness and security too, which Ponytail's review specifically doesn't focus on.
Avoid if
You're not using one of its 14+ supported agents; check compatibility first.
Workflow
Install Ponytail into your agent (a plugin command for Claude Code, similar routes for other supported agents) → pick an intensity level matching how aggressively you want it enforced → give the agent a normal coding task → compare the result against what the agent would have produced unprompted → run /ponytail-review on existing code to flag complexity worth removing.
Cost
Ponytail itself is free and MIT-licensed. It's a skill/ruleset layered onto an agent you're already paying for (through that agent's own subscription or API costs), so there's no separate fee. Running effort is minimal: install once, pick an intensity level, and occasionally run its review commands (like /ponytail-review) to audit existing code.
Restrictions
It only works within its 14+ supported agents and needs that underlying agent's own subscription or API access; Ponytail adds no model access of its own. Its published benchmark reflects one specific repo (FastAPI + React) and model (Haiku 4.5), not a universal guarantee.
First project
Documentation-based suggestion — not run here.
Read first project
Compare a task with and without Ponytail active.
Pick a small, real coding task you'd normally hand to your agent (add a feature, fix a bug).
Run it once without Ponytail installed, and note the approach (new dependencies added, lines of code, new abstractions).
Install Ponytail at "full" intensity and run the same task again in a fresh session.
Compare the two results: did Ponytail's version use an existing library instead of new code, or produce a shorter, simpler diff?
Done when you've compared both versions concretely (dependencies added, lines changed) and can describe specifically what Ponytail changed about the agent's approach, not just a vague impression.
Links & evidence
Documentation-based · not hands-on · Sep 23, 2026
Rests on Ponytail's homepage and GitHub repository, checked 23 September 2026. No agent session was run with or without Ponytail for this review.
An MIT-licensed ruleset for making coding agents write the least code that works.
Dietrich Gebert · free · desktop
coding-agent-ruleset
project-simplification
coding
code-maintenance
View sourced imagePonytail 4.9.0 configured in a fresh OpenCode 1.18.25 host, with its command menu available and full mode set in the isolated profile. This is configuration/activation evidence only: no command was submitted and no model was run.
Isolated local OpenCode host with the existing Ponytail plugin
