# Extension reference

This guide covers the `gemini extensions` commands and the structure of the
`gemini-extension.json` configuration file.

## Manage extensions

Use the `gemini extensions` command group to manage your extensions from the
terminal.

Note that commands like `gemini extensions install` are not supported within the
CLI's interactive mode. However, you can use the `/extensions list` command to
view installed extensions. All management operations, including updates to slash
commands, take effect only after you restart the CLI session.

### Install an extension

Install an extension by providing its GitHub repository URL or a local file
path.

Gemini CLI creates a copy of the extension during installation. You must run
`gemini extensions update` to pull changes from the source. To install from
GitHub, you must have `git` installed on your machine.

```bash
gemini extensions install <source> [--ref <ref>] [--auto-update] [--pre-release] [--consent] [--skip-settings]
```

- `<source>`: The GitHub URL or local path of the extension.
- `--ref`: The git ref (branch, tag, or commit) to install.
- `--auto-update`: Enable automatic updates for this extension.
- `--pre-release`: Enable installation of pre-release versions.
- `--consent`: Acknowledge security risks and skip the confirmation prompt.
- `--skip-settings`: Skip the configuration on install process.

### Uninstall an extension

To uninstall one or more extensions, use the `uninstall` command:

```bash
gemini extensions uninstall <name...>
```

### Disable an extension

Extensions are enabled globally by default. You can disable an extension
entirely or for a specific workspace.

```bash
gemini extensions disable <name> [--scope <scope>]
```

- `<name>`: The name of the extension to disable.
- `--scope`: The scope to disable the extension in (`user` or `workspace`).

### Enable an extension

Re-enable a disabled extension using the `enable` command:

```bash
gemini extensions enable <name> [--scope <scope>]
```

- `<name>`: The name of the extension to enable.
- `--scope`: The scope to enable the extension in (`user` or `workspace`).

### Update an extension

Update an extension to the version specified in its `gemini-extension.json`
file.

```bash
gemini extensions update <name>
```

To update all installed extensions at once:

```bash
gemini extensions update --all
```

### Create an extension from a template

Create a new extension directory using a built-in template.

```bash
gemini extensions new <path> [template]
```

- `<path>`: The directory to create.
- `[template]`: The template to use (for example, `mcp-server`, `context`,
  `custom-commands`).

### Link a local extension

Create a symbolic link between your development directory and Gemini CLI
extensions directory. This lets you test changes immediately without
reinstalling.

```bash
gemini extensions link <path>
```

## Extension format

Gemini CLI loads extensions from `<home>/.gemini/extensions`. Each extension
must have a `gemini-extension.json` file in its root directory.

### `gemini-extension.json`

The manifest file defines the extension's behavior and configuration.

```json
{
  "name": "my-extension",
  "version": "1.0.0",
  "description": "My awesome extension",
  "mcpServers": {
    "my-server": {
      "command": "node",
      "args": ["${extensionPath}/my-server.js"],
      "cwd": "${extensionPath}"
    }
  },
  "contextFileName": "GEMINI.md",
  "excludeTools": ["run_shell_command"],
  "migratedTo": "https://github.com/new-owner/new-extension-repo",
  "plan": {
    "directory": ".gemini/plans"
  }
}
```

- `name`: The name of the extension. This is used to uniquely identify the
  extension and for conflict resolution when extension commands have the same
  name as user or project commands. The name should be lowercase or numbers and
  use dashes instead of underscores or spaces. This is how users will refer to
  your extension in the CLI. Note that we expect this name to match the
  extension directory name.
- `version`: The version of the extension.
- `description`: A short description of the extension. This will be displayed on
  [geminicli.com/extensions](https://geminicli.com/extensions).
- `migratedTo`: The URL of the new repository source for the extension. If this
  is set, the CLI will automatically check this new source for updates and
  migrate the extension's installation to the new source if an update is found.
- `mcpServers`: A map of MCP servers to settings. The key is the name of the
  server, and the value is the server configuration. These servers will be
  loaded on startup just like MCP servers defined in a
  [`settings.json` file](../reference/configuration.md). If both an extension
  and a `settings.json` file define an MCP server with the same name, the server
  defined in the `settings.json` file takes precedence.
  - Note that all MCP server configuration options are supported except for
    `trust`.
  - For portability, you should use `${extensionPath}` to refer to files within
    your extension directory.
  - Separate your executable and its arguments using `command` and `args`
    instead of putting them both in `command`.
- `contextFileName`: The name of the file that contains the context for the
  extension. This will be used to load the context from the extension directory.
  If this property is not used but a `GEMINI.md` file is present in your
  extension directory, then that file will be loaded.
- `excludeTools`: An array of tool names to exclude from the model. You can also
  specify command-specific restrictions for tools that support it, like the
  `run_shell_command` tool. For example,
  `"excludeTools": ["run_shell_command(rm -rf)"]` will block the `rm -rf`
  command. Note that this differs from the MCP server `excludeTools`
  functionality, which can be listed in the MCP server config.
- `plan`: Planning features configuration.
  - `directory`: The directory where planning artifacts are stored. This serves
    as a fallback if the user hasn't specified a plan directory in their
    settings. If not specified by either the extension or the user, the default
    is `~/.gemini/tmp/<project>/<session-id>/plans/`.

When Gemini CLI starts, it loads all the extensions and merges their
configurations. If there are any conflicts, the workspace configuration takes
precedence.

### Extension settings

Extensions can define settings that users provide during installation, such as
API keys or URLs. These values are stored in a `.env` file within the extension
directory.

To define settings, add a `settings` array to your manifest:

```json
{
  "name": "my-api-extension",
  "version": "1.0.0",
  "settings": [
    {
      "name": "API Key",
      "description": "Your API key for the service.",
      "envVar": "MY_API_KEY",
      "sensitive": true
    }
  ]
}
```

- `name`: The setting's display name.
- `description`: A clear explanation of the setting.
- `envVar`: The environment variable name where the value is stored.
- `sensitive`: If `true`, the value is stored in the system keychain and
  obfuscated in the UI.

To update an extension's settings:

```bash
gemini extensions config <name> [setting] [--scope <scope>]
```

#### Environment variable sanitization

For security reasons, sensitive environment variables are filtered out and not
passed to extensions or MCP servers by default.

Extensions **will not** inherit the user's full shell environment variables.
They will only have access to:

1. Standard safe variables (e.g., `HOME`, `PATH`, `TMPDIR`).
2. Variables explicitly declared and requested in the `gemini-extension.json`
   manifest via the `settings` array (using the `envVar` property).

If your extension requires specific environment variables (like an API key,
custom host, or config path), you **must** declare them in the `settings` array
so the CLI can allowlist them for use within the extension.

### Custom commands

Provide [custom commands](../cli/custom-commands.md) by placing TOML files in a
`commands/` subdirectory. Gemini CLI uses the directory structure to determine
the command name.

For an extension named `gcp`:

- `commands/deploy.toml` becomes `/deploy`
- `commands/gcs/sync.toml` becomes `/gcs:sync` (namespaced with a colon)

### Hooks

Intercept and customize CLI behavior using [hooks](../hooks/index.md). Define
hooks in a `hooks/hooks.json` file within your extension directory. Note that
hooks are not defined in the `gemini-extension.json` manifest.

### Agent skills

Bundle [agent skills](../cli/skills.md) to provide specialized workflows. Place
skill definitions in a `skills/` directory. For example,
`skills/security-audit/SKILL.md` exposes a `security-audit` skill.

### Sub-agents

<!-- prettier-ignore -->
> [!NOTE]
> Sub-agents are a preview feature currently under active development.

Provide [sub-agents](../core/subagents.md) that users can delegate tasks to. Add
agent definition files (`.md`) to an `agents/` directory in your extension root.

### <a id="policy-engine"></a>Policy Engine

Extensions can contribute policy rules and safety checkers to Gemini CLI
[Policy Engine](../reference/policy-engine.md). These rules are defined in
`.toml` files and take effect when the extension is activated.

To add policies, create a `policies/` directory in your extension's root and
place your `.toml` policy files inside it. Gemini CLI automatically loads all
`.toml` files from this directory.

Rules contributed by extensions run in their own tier (tier 2), alongside
workspace-defined policies. This tier has higher priority than the default rules
but lower priority than user or admin policies.

<!-- prettier-ignore -->
> [!WARNING]
> For security, Gemini CLI ignores any `allow` decisions or `yolo`
> mode configurations in extension policies. This ensures that an extension
> cannot automatically approve tool calls or bypass security measures without
> your confirmation.

**Example `policies.toml`**

```toml
[[rule]]
mcpName = "my_server"
toolName = "dangerous_tool"
decision = "ask_user"
priority = 100

[[safety_checker]]
mcpName = "my_server"
toolName = "write_data"
priority = 200
[safety_checker.checker]
type = "in-process"
name = "allowed-path"
required_context = ["environment"]
```

### Themes

Extensions can provide custom themes to personalize the CLI UI. Themes are
defined in the `themes` array in `gemini-extension.json`.

**Example**

```json
{
  "name": "my-green-extension",
  "version": "1.0.0",
  "themes": [
    {
      "name": "shades-of-green",
      "type": "custom",
      "background": {
        "primary": "#1a362a"
      },
      "text": {
        "primary": "#a6e3a1",
        "secondary": "#6e8e7a",
        "link": "#89e689"
      },
      "status": {
        "success": "#76c076",
        "warning": "#d9e689",
        "error": "#b34e4e"
      },
      "border": {
        "default": "#4a6c5a"
      },
      "ui": {
        "comment": "#6e8e7a"
      }
    }
  ]
}
```

Custom themes provided by extensions can be selected using the `/theme` command
or by setting the `ui.theme` property in your `settings.json` file. Note that
when referring to a theme from an extension, the extension name is appended to
the theme name in parentheses, for example,
`shades-of-green (my-green-extension)`.

### Conflict resolution

Extension commands have the lowest precedence. If an extension command name
conflicts with a user or project command, the extension command is prefixed with
the extension name (for example, `/gcp.deploy`) using a dot separator.

## Variables

Gemini CLI supports variable substitution in `gemini-extension.json` and
`hooks/hooks.json`.

| Variable           | Description                                     |
| :----------------- | :---------------------------------------------- |
| `${extensionPath}` | The absolute path to the extension's directory. |
| `${workspacePath}` | The absolute path to the current workspace.     |
| `${/}`             | The platform-specific path separator.           |
