🪴 Brain

Ponytail

3 min read

🚀 Ponytail — makes your AI agent think like the laziest senior dev in the room. The best code is the code you never wrote.

📒 The Principle

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

  1. Does this need to exist? → no: skip it (YAGNI)
  2. Already in this codebase? → reuse it, don’t rewrite
  3. Stdlib does it? → use it
  4. Native platform feature? → use it
  5. Installed dependency? → use it
  6. One line? → one line
  7. Only then: the minimum that works

Lazy about the solution, never about reading.

📊 Measured Impact (on real Claude Code sessions, n=12 on FastAPI + React)

  • −54% LOC (mean; up to −94% where overbuild trap exists like date picker)
  • −22% tokens
  • −20% cost
  • −27% wall-clock time
  • 100% safety — validation, error-handling, security, accessibility never cut

Compare: caveman (terse prose) does −20% LOC but +7% tokens. YAGNI-alone prompt does −33% LOC but drops to 95% safety.

🔗 Installation

Cross-harness support:

HostCommand
Claude Code/plugin marketplace add DietrichGebert/ponytail
/plugin install ponytail@ponytail
Codexcodex plugin marketplace add DietrichGebert/ponytail
Then /plugins → install Ponytail + trust hooks
Copilot CLIcopilot plugin marketplace add DietrichGebert/ponytail
copilot plugin install ponytail@ponytail
Gemini CLIgemini extensions install https://github.com/DietrichGebert/ponytail
Cursor / Windsurf / ClineCopy .cursor/rules/ponytail.md to your project’s .cursor/rules/
VS Code (Codex)~/.codex/AGENTS.md (loaded auto)
GitHub Copilot (fallback)Copy rules to ~/.copilot/copilot-instructions.md

🎚️ Modes (per-session, via /ponytail [lite|full|ultra|off])

Default: full. Set globally via PONYTAIL_DEFAULT_MODE env var or ~/.config/ponytail/config.json.

✍️ Commands

CommandPurpose
/ponytail [lite|full|ultra|off]Set intensity or toggle. No arg = report current.
/ponytail-reviewReview the diff for over-engineering; hands back a delete-list.
/ponytail-auditAudit the whole repo for over-engineering, not just diff.
/ponytail-debtHarvest deferred ponytail: shortcuts into a ledger (‘later’ → ‘never’).
/ponytail-gainShow the measured impact scoreboard (less code, less cost, more speed).
/ponytail-helpQuick reference.

🧩 Features

  • Structured output — reasoning before suggestion, chain-of-thought validation
  • Syntax coverage — 9 loop transformations (Fusion, Interchange, Parallelization, Tiling, Unrolling, Skewing, Reversal), source-level & IR-level
  • Safety-first — trust boundary validation, data-loss handling, security, accessibility stay
  • Zero config — optional ~/.config/ponytail/config.json for defaults

🔍 When It Shines

  • Date pickers: 404 LOC → 23 LOC (uses native <input type="date"> instead of npm bloat)
  • Color pickers: 287 LOC → 23 LOC
  • Reuse patterns: agent re-reads code, avoids 3x rewrites
  • Code-completion bloat: stops the “just add another utility” impulse

🔗 Links

Further Reading

Graph View

Backlinks