# Claude Code

## Quick start

examples/claude/server.ts:

```ts
import { agentOS, setup } from "@rivet-dev/agentos";
import claude from "@agentos-software/claude-code";

const vm = agentOS({ software: [claude] });

export const registry = setup({ use: { vm } });
registry.start();
```

client.ts:

```ts
await agent.sessions.open({
	agent: "claude",
	env: { ANTHROPIC_API_KEY: process.env.ANTHROPIC_API_KEY! },
});

const result = await agent.sessions.prompt({
	content: [
		{ type: "text", text: "What files are in the current directory?" },
	],
});
console.log(result.message?.content ?? []);
```

Read [Sessions](/agentos/docs/sessions) first for session options, streaming events, prompts, and lifecycle management.

## Model & credentials

Set the relevant variable(s) on the session's `env`, sourced from your server's environment:

- `ANTHROPIC_API_KEY` — Anthropic API key (direct API).
- `ANTHROPIC_AUTH_TOKEN` — bearer token for proxy / OAuth auth.
- `ANTHROPIC_BASE_URL` — route through a gateway or proxy endpoint.
- `ANTHROPIC_MODEL` — override the default model.
- `CLAUDE_CODE_USE_BEDROCK=1` — use Amazon Bedrock (auth via the AWS credential chain: `AWS_REGION`, `AWS_PROFILE`, …).
- `CLAUDE_CODE_USE_VERTEX=1` — use Google Vertex AI (auth via Google Cloud credentials).

See [Models & Credentials](/agentos/docs/models-and-credentials), and Claude Code's [environment variables](https://code.claude.com/docs/en/env-vars) for the full list.

## Skills

Claude Code discovers [agent skills](https://docs.claude.com/en/docs/claude-code/skills) from `SKILL.md` files under its skills directory. Write the skill into the VM before creating a session and Claude Code loads it automatically.

client.ts:

```ts
	const skill = `---
name: commit-style
description: How to write commit messages in this project.
---

Write commit messages in the imperative mood and keep the subject under 50 characters.
`;

	// Write the skill before creating the session
	await agent.filesystem.mkdir("/home/agentos/.claude/skills/commit-style");
	await agent.filesystem.writeFile(
		"/home/agentos/.claude/skills/commit-style/SKILL.md",
		skill,
	);

	// Claude Code discovers the skill automatically
	await agent.sessions.open({
		agent: "claude",
		env: { ANTHROPIC_API_KEY: process.env.ANTHROPIC_API_KEY! },
	});
```

## MCP servers

Expose extra tools to the agent by passing `mcpServers` to `openSession`. Both local child-process servers and remote URLs are supported.

client.ts:

```ts
const mcpConfig = {
	mcpServers: {
		filesystem: {
			command: "npx",
			args: [
				"-y",
				"@modelcontextprotocol/server-filesystem",
				"/home/agentos",
			],
		},
		remote: {
			type: "sse",
			url: "https://mcp.example.com/sse",
			headers: { Authorization: "Bearer my-token" },
		},
	},
};
await agent.filesystem.writeFile(
	"/home/agentos/.claude.json",
	JSON.stringify(mcpConfig),
);

await agent.sessions.open({
	agent: "claude",
	env: { ANTHROPIC_API_KEY: process.env.ANTHROPIC_API_KEY! },
});
```

> **NOTE:** **Pre-install `npx`-launched servers.** A local server started with `npx -y …` writes install progress to **stdout** on its first run, which corrupts the MCP stdio handshake (you'll see `Connection closed`). Pre-install it in the VM so `npx` is silent — `await agent.process.exec("npm install -g @modelcontextprotocol/server-filesystem")` before the session — or pin the package and point `command` at the installed binary.

## Customizing the agent

Claude Code is a built-in agent, but it's just a software package under the hood. To ship your own ACP adapter, swap the underlying agent SDK, or register a tweaked build as a new agent, see [Custom Agents](/agentos/docs/agents/custom).