Ponytail

Ponytail is a ruleset for AI coding agents that pushes them to write the least code that works. Now in version 5, it installs into an agent in two lines and changes how the agent approaches a task: it reads the existing code and traces the real flow first, then climbs a ladder of questions. Does this need to exist, is it already in the codebase, does the standard library or the platform provide it, does an installed dependency solve it, can it be one line. Only then does it write the minimum that works. It is aimed at developers who use coding agents and want smaller, easier to review changes. The vendor reports results from a benchmark of 39 tasks with five runs each on Opus 5.5, claiming 53 percent fewer lines of code, 45 percent fewer output tokens, 26 percent lower cost and 41 percent less time, with hidden correctness checks passing at comparable rates. It states that validation, error handling, security and accessibility are never simplified away, and that risky logic such as branches, loops, parsers, money and security code ships with one small test. A review command reads the code a change touches rather than only the diff and reports bugs, security issues, load problems, missing tests and code to cut, and an audit command does the same across a whole repository. The site does not publish pricing or licensing terms. The vendor is also collecting customer stories for publication.