# Remote Subagents (experimental)

Gemini CLI supports connecting to remote subagents using the Agent-to-Agent
(A2A) protocol. This allows Gemini CLI to interact with other agents, expanding
its capabilities by delegating tasks to remote services.

Gemini CLI can connect to any compliant A2A agent. You can find samples of A2A
agents in the following repositories:

- [ADK Samples (Python)](https://github.com/google/adk-samples/tree/main/python)
- [ADK Python Contributing Samples](https://github.com/google/adk-python/tree/main/contributing/samples)

> **Note: Remote subagents are currently an experimental feature.**

## Configuration

To use remote subagents, you must explicitly enable them in your
`settings.json`:

```json
{
  "experimental": {
    "enableAgents": true
  }
}
```

## Proxy support

Gemini CLI routes traffic to remote agents through an HTTP/HTTPS proxy if one is
configured. It uses the `general.proxy` setting in your `settings.json` file or
standard environment variables (`HTTP_PROXY`, `HTTPS_PROXY`).

```json
{
  "general": {
    "proxy": "http://my-proxy:8080"
  }
}
```

## Defining remote subagents

Remote subagents are defined as Markdown files (`.md`) with YAML frontmatter.
You can place them in:

1.  **Project-level:** `.gemini/agents/*.md` (Shared with your team)
2.  **User-level:** `~/.gemini/agents/*.md` (Personal agents)

### Configuration schema

| Field            | Type   | Required | Description                                                                                                    |
| :--------------- | :----- | :------- | :------------------------------------------------------------------------------------------------------------- |
| `kind`           | string | Yes      | Must be `remote`.                                                                                              |
| `name`           | string | Yes      | A unique name for the agent. Must be a valid slug (lowercase letters, numbers, hyphens, and underscores only). |
| `agent_card_url` | string | Yes      | The URL to the agent's A2A card endpoint.                                                                      |
| `auth`           | object | No       | Authentication configuration. See [Authentication](#authentication).                                           |

### Single-subagent example

```markdown
---
kind: remote
name: my-remote-agent
agent_card_url: https://example.com/agent-card
---
```

### Multi-subagent example

The loader explicitly supports multiple remote subagents defined in a single
Markdown file.

```markdown
---
- kind: remote
  name: remote-1
  agent_card_url: https://example.com/1
- kind: remote
  name: remote-2
  agent_card_url: https://example.com/2
---
```

> **Note:** Mixed local and remote agents, or multiple local agents, are not
> supported in a single file; the list format is currently remote-only.

## Authentication

Many remote agents require authentication. Gemini CLI supports several
authentication methods aligned with the
[A2A security specification](https://a2a-protocol.org/latest/specification/#451-securityscheme).
Add an `auth` block to your agent's frontmatter to configure credentials.

### Supported auth types

Gemini CLI supports the following authentication types:

| Type                 | Description                                                                                    |
| :------------------- | :--------------------------------------------------------------------------------------------- |
| `apiKey`             | Send a static API key as an HTTP header.                                                       |
| `http`               | HTTP authentication (Bearer token, Basic credentials, or any IANA-registered scheme).          |
| `google-credentials` | Google Application Default Credentials (ADC). Automatically selects access or identity tokens. |
| `oauth2`             | OAuth 2.0 Authorization Code flow with PKCE. Opens a browser for interactive sign-in.          |

### Dynamic values

For `apiKey` and `http` auth types, secret values (`key`, `token`, `username`,
`password`, `value`) support dynamic resolution:

| Format      | Description                                         | Example                    |
| :---------- | :-------------------------------------------------- | :------------------------- |
| `$ENV_VAR`  | Read from an environment variable.                  | `$MY_API_KEY`              |
| `!command`  | Execute a shell command and use the trimmed output. | `!gcloud auth print-token` |
| literal     | Use the string as-is.                               | `sk-abc123`                |
| `$$` / `!!` | Escape prefix. `$$FOO` becomes the literal `$FOO`.  | `$$NOT_AN_ENV_VAR`         |

> **Security tip:** Prefer `$ENV_VAR` or `!command` over embedding secrets
> directly in agent files, especially for project-level agents checked into
> version control.

### API key (`apiKey`)

Sends an API key as an HTTP header on every request.

| Field  | Type   | Required | Description                                           |
| :----- | :----- | :------- | :---------------------------------------------------- |
| `type` | string | Yes      | Must be `apiKey`.                                     |
| `key`  | string | Yes      | The API key value. Supports dynamic values.           |
| `name` | string | No       | Header name to send the key in. Default: `X-API-Key`. |

```yaml
---
kind: remote
name: my-agent
agent_card_url: https://example.com/agent-card
auth:
  type: apiKey
  key: $MY_API_KEY
---
```

### HTTP authentication (`http`)

Supports Bearer tokens, Basic auth, and arbitrary IANA-registered HTTP
authentication schemes.

#### Bearer token

Use the following fields to configure a Bearer token:

| Field    | Type   | Required | Description                                |
| :------- | :----- | :------- | :----------------------------------------- |
| `type`   | string | Yes      | Must be `http`.                            |
| `scheme` | string | Yes      | Must be `Bearer`.                          |
| `token`  | string | Yes      | The bearer token. Supports dynamic values. |

```yaml
auth:
  type: http
  scheme: Bearer
  token: $MY_BEARER_TOKEN
```

#### Basic authentication

Use the following fields to configure Basic authentication:

| Field      | Type   | Required | Description                            |
| :--------- | :----- | :------- | :------------------------------------- |
| `type`     | string | Yes      | Must be `http`.                        |
| `scheme`   | string | Yes      | Must be `Basic`.                       |
| `username` | string | Yes      | The username. Supports dynamic values. |
| `password` | string | Yes      | The password. Supports dynamic values. |

```yaml
auth:
  type: http
  scheme: Basic
  username: $MY_USERNAME
  password: $MY_PASSWORD
```

#### Raw scheme

For any other IANA-registered scheme (for example, Digest, HOBA), provide the
raw authorization value.

| Field    | Type   | Required | Description                                                                   |
| :------- | :----- | :------- | :---------------------------------------------------------------------------- |
| `type`   | string | Yes      | Must be `http`.                                                               |
| `scheme` | string | Yes      | The scheme name (for example, `Digest`).                                      |
| `value`  | string | Yes      | Raw value sent as `Authorization: <scheme> <value>`. Supports dynamic values. |

```yaml
auth:
  type: http
  scheme: Digest
  value: $MY_DIGEST_VALUE
```

### Google Application Default Credentials (`google-credentials`)

Uses
[Google Application Default Credentials (ADC)](https://cloud.google.com/docs/authentication/application-default-credentials)
to authenticate with Google Cloud services and Cloud Run endpoints. This is the
recommended auth method for agents hosted on Google Cloud infrastructure.

| Field    | Type     | Required | Description                                                                 |
| :------- | :------- | :------- | :-------------------------------------------------------------------------- |
| `type`   | string   | Yes      | Must be `google-credentials`.                                               |
| `scopes` | string[] | No       | OAuth scopes. Defaults to `https://www.googleapis.com/auth/cloud-platform`. |

```yaml
---
kind: remote
name: my-gcp-agent
agent_card_url: https://my-agent-xyz.run.app/.well-known/agent.json
auth:
  type: google-credentials
---
```

#### How token selection works

The provider automatically selects the correct token type based on the agent's
host:

| Host pattern       | Token type         | Use case                                    |
| :----------------- | :----------------- | :------------------------------------------ |
| `*.googleapis.com` | **Access token**   | Google APIs (Agent Engine, Vertex AI, etc.) |
| `*.run.app`        | **Identity token** | Cloud Run services                          |

- **Access tokens** authorize API calls to Google services. They are scoped
  (default: `cloud-platform`) and fetched via `GoogleAuth.getClient()`.
- **Identity tokens** prove the caller's identity to a service that validates
  the token's audience. The audience is set to the target host. These are
  fetched via `GoogleAuth.getIdTokenClient()`.

Both token types are cached and automatically refreshed before expiry.

#### Setup

`google-credentials` relies on ADC, which means your environment must have
credentials configured. Common setups:

- **Local development:** Run `gcloud auth application-default login` to
  authenticate with your Google account.
- **CI / Cloud environments:** Use a service account. Set the
  `GOOGLE_APPLICATION_CREDENTIALS` environment variable to the path of your
  service account key file, or use workload identity on GKE / Cloud Run.

#### Allowed hosts

For security, `google-credentials` only sends tokens to known Google-owned
hosts:

- `*.googleapis.com`
- `*.run.app`

Requests to any other host will be rejected with an error. If your agent is
hosted on a different domain, use one of the other auth types (`apiKey`, `http`,
or `oauth2`).

#### Examples

The following examples demonstrate how to configure Google Application Default
Credentials.

**Cloud Run agent:**

```yaml
---
kind: remote
name: cloud-run-agent
agent_card_url: https://my-agent-xyz.run.app/.well-known/agent.json
auth:
  type: google-credentials
---
```

**Google API with custom scopes:**

```yaml
---
kind: remote
name: vertex-agent
agent_card_url: https://us-central1-aiplatform.googleapis.com/.well-known/agent.json
auth:
  type: google-credentials
  scopes:
    - https://www.googleapis.com/auth/cloud-platform
    - https://www.googleapis.com/auth/compute
---
```

### OAuth 2.0 (`oauth2`)

Performs an interactive OAuth 2.0 Authorization Code flow with PKCE. On first
use, Gemini CLI opens your browser for sign-in and persists the resulting tokens
for subsequent requests.

| Field               | Type     | Required | Description                                                                                                                                        |
| :------------------ | :------- | :------- | :------------------------------------------------------------------------------------------------------------------------------------------------- |
| `type`              | string   | Yes      | Must be `oauth2`.                                                                                                                                  |
| `client_id`         | string   | Yes\*    | OAuth client ID. Required for interactive auth.                                                                                                    |
| `client_secret`     | string   | No\*     | OAuth client secret. Required by most authorization servers (confidential clients). Can be omitted for public clients that don't require a secret. |
| `scopes`            | string[] | No       | Requested scopes. Can also be discovered from the agent card.                                                                                      |
| `authorization_url` | string   | No       | Authorization endpoint. Discovered from the agent card if omitted.                                                                                 |
| `token_url`         | string   | No       | Token endpoint. Discovered from the agent card if omitted.                                                                                         |

```yaml
---
kind: remote
name: oauth-agent
agent_card_url: https://example.com/.well-known/agent.json
auth:
  type: oauth2
  client_id: my-client-id.apps.example.com
---
```

If the agent card advertises an `oauth2` security scheme with
`authorizationCode` flow, the `authorization_url`, `token_url`, and `scopes` are
automatically discovered. You only need to provide `client_id` (and
`client_secret` if required).

Tokens are persisted to disk and refreshed automatically when they expire.

### Auth validation

When Gemini CLI loads a remote agent, it validates your auth configuration
against the agent card's declared `securitySchemes`. If the agent requires
authentication that you haven't configured, you'll see an error describing
what's needed.

`google-credentials` is treated as compatible with `http` Bearer security
schemes, since it produces Bearer tokens.

### Auth retry behavior

All auth providers automatically retry on `401` and `403` responses by
re-fetching credentials (up to 2 retries). This handles cases like expired
tokens or rotated credentials. For `apiKey` with `!command` values, the command
is re-executed on retry to fetch a fresh key.

### Agent card fetching and auth

When connecting to a remote agent, Gemini CLI first fetches the agent card
**without** authentication. If the card endpoint returns a `401` or `403`, it
retries the fetch **with** the configured auth headers. This lets agents have
publicly accessible cards while protecting their task endpoints, or to protect
both behind auth.

## Managing Subagents

Users can manage subagents using the following commands within the Gemini CLI:

- `/agents list`: Displays all available local and remote subagents.
- `/agents reload`: Reloads the agent registry. Use this after adding or
  modifying agent definition files.
- `/agents enable <agent_name>`: Enables a specific subagent.
- `/agents disable <agent_name>`: Disables a specific subagent.

> **Tip:** You can use the `@cli_help` agent within Gemini CLI for assistance
> with configuring subagents.
