How to Install Ponytail for Gemini CLI or Antigravity CLI

Install Ponytail as a Gemini CLI extension using gemini extensions install https://github.com/DietrichGebert/ponytail, or use agy plugin install https://github.com/DietrichGebert/ponytail for Antigravity CLI; the gemini-extension.json manifest automatically registers six slash commands and injects the AGENTS.md ruleset into every LLM context window.

Ponytail is an always-on coding assistant distributed as a native extension for Google's Gemini CLI and its successor, Antigravity CLI. According to the DietrichGebert/ponytail repository source code, the extension leverages a declarative manifest system to inject behavioral rules and register slash commands without requiring manual file copying or hook configuration.

How the Ponytail Extension Works

The installation process relies on gemini-extension.json, the manifest file located in the repository root that tells the CLI how to load Ponytail. When you install the extension, the CLI performs three actions automatically:

• Ruleset injection – The guidance defined in AGENTS.md is injected as context for every LLM turn, making Ponytail’s coding standards always active.
• Skill registration – The TypeScript files under the skills/ directory are discovered and compiled into the six /ponytail* commands.
• Zero-hook loading – Gemini auto-loads the extension’s manifest directly; Ponytail does not ship a root hooks/hooks.json because the CLI already knows where to look based on the manifest declaration.

Installing Ponytail in Gemini CLI

To install Ponytail for Gemini CLI, run the following command in your terminal:

gemini extensions install https://github.com/DietrichGebert/ponytail

This command downloads the repository, parses gemini-extension.json, and registers the extension. Once complete, the skills/ directory is mounted and the commands become available immediately in new Gemini sessions.

Installing Ponytail in Antigravity CLI

For Antigravity CLI (the successor to Gemini CLI), use the agy command with the plugin subcommand:

agy plugin install https://github.com/DietrichGebert/ponytail

Antigravity reads the same gemini-extension.json manifest structure, ensuring compatibility across both CLI versions without modification to the extension source code.

Available Ponytail Commands

After installation, the following slash commands are registered from the skills/ directory:

• /ponytail – Toggles the assistant mode or displays current configuration status.
• /ponytail-review – Runs the review skill on the current git diff.
• /ponytail-audit – Performs a comprehensive codebase audit against Ponytail's ruleset.
• /ponytail-debt – Identifies and categorizes technical debt in the current project.
• /ponytail-gain – Suggests performance or architectural improvements.
• /ponytail-help – Displays help documentation for Ponytail commands.

Manual Ruleset Installation (Optional)

If you prefer not to install the full extension but want the always-on behavior, you can manually copy the ruleset to your agents configuration directory:

cp AGENTS.md ~/.agents/rules/ponytail.md

This method injects the AGENTS.md content into every LLM turn without registering the /ponytail* commands, useful for lightweight setups where you only need the behavioral guardrails.

Summary

• Ponytail installs as a native extension via gemini extensions install or agy plugin install.
• The gemini-extension.json manifest drives automatic loading of rules from AGENTS.md and commands from the skills/ directory.
• Six slash commands (/ponytail, /ponytail-review, /ponytail-audit, /ponytail-debt, /ponytail-gain, /ponytail-help) become available immediately after installation.
• No manual hook configuration is required; Gemini and Antigravity parse the manifest automatically.
• Alternatively, copy AGENTS.md to ~/.agents/rules/ponytail.md for rules-only operation without command registration.

Frequently Asked Questions

Do I need to manually copy files to install Ponytail for Gemini CLI?

No manual file copying is necessary. The gemini extensions install command handles the entire installation by reading the gemini-extension.json manifest, which specifies the location of the AGENTS.md ruleset and the skills/ directory.

What is the difference between installing Ponytail in Gemini CLI versus Antigravity CLI?

There is no functional difference in the extension behavior. Both CLIs consume the same gemini-extension.json manifest and load identical rulesets and commands. The only variation is the installation command: gemini extensions install versus agy plugin install.

Where does Ponytail store its always-on ruleset?

The canonical ruleset lives in the repository's AGENTS.md file. When you install the extension, the CLI reads this file and injects its contents into the system prompt for every LLM interaction. You can also manually place this file in ~/.agents/rules/ponytail.md to achieve similar behavior without the full extension.

Can I use Ponytail commands without installing the full extension?

No. The six /ponytail* commands are implemented as skills within the skills/ directory and require the extension installation to register with the CLI's command parser. However, you can use the AGENTS.md ruleset independently by copying it to your agents rules directory, though this only provides the behavioral guidance, not the interactive commands.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}