Purpose
Ask an AI assistant to make a small change and it may add new settings, one-use helpers, or a dependency. Ponytail is a set of working rules for coding assistants. Before editing, it asks them to identify the affected code, callers, and tests, then find a simple way to complete the task.
It favors existing project code, platform features, and installed dependencies. When new code is needed, the aim is to write enough clear code to finish the job. Its focus is the smallest complete change, including every affected part, rather than the fewest lines. The official core Skill describes these trade-offs and the safeguards that must remain.
When to use it
If a project already has a reliable component or utility but an assistant keeps creating a second version, Ponytail can prompt it to check what exists first. Small fixes, new fields, and dependency choices make this especially easy to see. The project also provides commands to review a change or audit a whole codebase for needless complexity.
We think it suits developers who can judge delivery quality and are willing to review changes. Where a project has explicit architectural or compliance needs, state the necessary design first; “write less” must not decide the scope of the requirement. That is our editorial judgment, not a result from testing Ponytail on this site.
Example
Suppose an existing list API needs a filter for active items only. You could ask the assistant:
Inspect this API’s query parameters, existing filters, and relevant tests. Then add the active-status filter using the current data flow. Check how invalid parameters are handled, and report what changed and what remains unverified.
In this hypothetical case, reusing existing parameter parsing and filter functions would usually fit the task better than building a general search framework. The new branch still needs an appropriate test, and shorter code is no reason to ignore bad input. This example illustrates a decision process; it does not claim Ponytail produced this result on a site API.
Limitations
Ponytail affects how an assistant chooses an approach. It cannot guarantee that the assistant understands the request, writes correct code, or finds every risk. Its rules explicitly keep necessary input validation, error handling that prevents data loss, security, and accessibility. People still need to review the result and run suitable tests.
The project’s performance numbers come from specific models and tasks. An independent JetBrains test of an earlier version reported different results from the project’s tests and did not prove equal quality across all tasks. We therefore do not treat any savings percentage or safety result as a promise for your project.
Installation
The following Codex and Claude Code steps come from the official installation guide. These are commands to read and run yourself; this page does not install anything.
In a terminal, run the Codex commands in order:
codex plugin marketplace add DietrichGebert/ponytail
codex plugin add ponytail@ponytailThen open /hooks in Codex, review and trust the two lifecycle hooks, and start a new conversation. For Codex desktop, the official instructions also say to restart the app after installation. The hooks use Node.js, so node must be on the executable path.
In Claude Code, send these as two separate prompts:
/plugin marketplace add DietrichGebert/ponytail
/plugin install ponytail@ponytailSee the official guide for other platforms. A rules file, an individual Skill, and the full plugin may be enabled differently in each tool.