Quick start

curl https://api.anthropic.com/v1/messages \
  -H "content-type: application/json" \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-opus-5",
    "max_tokens": 1024,
    "tools": [
      {
        "type": "bash_20250124",
        "name": "bash"
      }
    ],
    "messages": [
      {
        "role": "user",
        "content": "List all Python files in the current directory."
      }
    ]
  }'

ant messages create \
  --model claude-opus-5 \
  --max-tokens 1024 \
  --tool '{type: bash_20250124, name: bash}' \
  --message '{role: user, content: List all Python files in the current directory.}'

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-opus-5",
    max_tokens=1024,
    tools=[{"type": "bash_20250124", "name": "bash"}],
    messages=[
        {"role": "user", "content": "List all Python files in the current directory."}
    ],
)

print(response)

const client = new Anthropic();

const response = await client.messages.create({
  model: "claude-opus-5",
  max_tokens: 1024,
  tools: [{ type: "bash_20250124", name: "bash" }],
  messages: [
    {
      role: "user",
      content: "List all Python files in the current directory."
    }
  ]
});

console.log(response);

var client = new AnthropicClient();

var response = await client.Messages.Create(
    new()
    {
        Model = Model.ClaudeOpus5,
        MaxTokens = 1024,
        Tools = [new ToolBash20250124()],
        Messages =
        [
            new()
            {
                Role = Role.User,
                Content = "List all Python files in the current directory.",
            },
        ],
    }
);

Console.WriteLine(response);

client := anthropic.NewClient()

response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
	Model:     anthropic.ModelClaudeOpus5,
	MaxTokens: 1024,
	Tools: []anthropic.ToolUnionParam{
		{OfBashTool20250124: &anthropic.ToolBash20250124Param{}},
	},
	Messages: []anthropic.MessageParam{
		anthropic.NewUserMessage(anthropic.NewTextBlock("List all Python files in the current directory.")),
	},
})
if err != nil {
	log.Fatal(err)
}
fmt.Println(response)

import com.anthropic.models.messages.ToolBash20250124;

void main() {
    AnthropicClient client = AnthropicOkHttpClient.fromEnv();

    Message response = client.messages().create(
        MessageCreateParams.builder()
            .model(Model.CLAUDE_OPUS_5)
            .maxTokens(1024)
            .addTool(ToolBash20250124.builder().build())
            .addUserMessage("List all Python files in the current directory.")
            .build()
    );

    IO.println(response);
}

use Anthropic\Messages\ToolBash20250124;

$client = new Client();

$response = $client->messages->create(
    model: 'claude-opus-5',
    maxTokens: 1024,
    tools: [new ToolBash20250124()],
    messages: [
        ['role' => 'user', 'content' => 'List all Python files in the current directory.'],
    ],
);

echo $response;

client = Anthropic::Client.new

response = client.messages.create(
  model: "claude-opus-5",
  max_tokens: 1024,
  tools: [{type: "bash_20250124", name: "bash"}],
  messages: [
    {role: "user", content: "List all Python files in the current directory."}
  ]
)

puts response

Claude responds with stop_reason: "tool_use" and a tool_use block that contains the command for your application to run:

{
  "id": "msg_01XAbCDeFgHiJkLmNoPQrStU",
  "model": "claude-opus-5",
  "stop_reason": "tool_use",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "I'll list all Python files in the current directory for you."
    },
    {
      "type": "tool_use",
      "id": "toolu_01A09q90qw90lq917835lq9",
      "name": "bash",
      "input": {
        "command": "ls *.py"
      }
    }
  ]
}

Run input.command in your bash session and send the output back as a tool_result. See Implement the bash tool for the round trip.