Strict Tool Use ↗

anthropic-platform guide intermediate tool-use agents
no

Original Documentation

Enforce JSON Schema compliance on Claude’s tool inputs with grammar-constrained sampling.

Setting strict: true on a tool definition uses grammar-constrained sampling to guarantee Claude’s tool inputs match your JSON Schema. This page covers why strict mode matters for agents, how to enable it, and common use cases. For the supported JSON Schema subset, see JSON Schema limitations. For non-strict schema guidance, see Define tools.

Strict tool use validates tool parameters, ensuring Claude calls your functions with correctly-typed arguments. Use strict tool use when you need to:

  • Validate tool parameters
  • Build agentic workflows
  • Ensure type-safe function calls
  • Handle complex tools with nested properties

Why strict tool use matters for agents#

Building reliable agentic systems requires guaranteed schema conformance. Without strict mode, Claude might return incompatible types ("2" instead of 2) or missing required fields, breaking your functions and causing runtime errors.

Strict tool use guarantees type-safe parameters:

  • Functions receive correctly-typed arguments every time
  • No need to validate and retry tool calls
  • Production-ready agents that work consistently at scale

For example, suppose a booking system needs passengers: int. Without strict mode, Claude might provide passengers: "two" or passengers: "2". With strict: true, the response will always contain passengers: 2.

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-4-6",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "What is the weather in San Francisco?"}
    ],
    "tools": [{
      "name": "get_weather",
      "description": "Get the current weather in a given location",
      "strict": true,
      "input_schema": {
        "type": "object",
        "properties": {
          "location": {
            "type": "string",
            "description": "The city and state, e.g. San Francisco, CA"
          },
          "unit": {
            "type": "string",
            "enum": ["celsius", "fahrenheit"]
          }
        },
        "required": ["location"],
        "additionalProperties": false
      }
    }]
  }'
import anthropic

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "What's the weather like in San Francisco?"}],
    tools=[
        {
            "name": "get_weather",
            "description": "Get the current weather in a given location",
            "strict": True,  # Enable strict mode
            "input_schema": {
                "type": "object",
                "properties": {
                    "location": {
                        "type": "string",
                        "description": "The city and state, e.g. San Francisco, CA",
                    },
                    "unit": {
                        "type": "string",
                        "enum": ["celsius", "fahrenheit"],
                        "description": "The unit of temperature, either 'celsius' or 'fahrenheit'",
                    },
                },
                "required": ["location"],
                "additionalProperties": False,
            },
        }
    ],
)
print(response.content)

const client = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY
});

const response = await client.messages.create({
  model: "claude-opus-4-6",
  max_tokens: 1024,
  messages: [
    {
      role: "user",
      content: "What's the weather like in San Francisco?"
    }
  ],
  tools: [
    {
      name: "get_weather",
      description: "Get the current weather in a given location",
      strict: true, // Enable strict mode
      input_schema: {
        type: "object",
        properties: {
          location: {
            type: "string",
            description: "The city and state, e.g. San Francisco, CA"
          },
          unit: {
            type: "string",
            enum: ["celsius", "fahrenheit"]
          }
        },
        required: ["location"],
        additionalProperties: false
      }
    }
  ]
});
console.log(response.content);
using System.Text.Json;
using Anthropic;
using Anthropic.Models.Messages;

public class Program
{
    public static async Task Main(string[] args)
    {
        AnthropicClient client = new();

        var parameters = new MessageCreateParams
        {
            Model = Model.ClaudeOpus4_6,
            MaxTokens = 1024,
            Messages = [new() { Role = Role.User, Content = "What's the weather like in San Francisco?" }],
            Tools = [
                new ToolUnion(new Tool()
                {
                    Name = "get_weather",
                    Description = "Get the current weather in a given location",
                    Strict = true,
                    InputSchema = new InputSchema(new Dictionary<string, JsonElement>
                    {
                        ["properties"] = JsonSerializer.SerializeToElement(new Dictionary<string, object>
                        {
                            ["location"] = new { type = "string", description = "The city and state, e.g. San Francisco, CA" },
                            ["unit"] = new { type = "string", @enum = new[] { "celsius", "fahrenheit" } },
                        }),
                        ["required"] = JsonSerializer.SerializeToElement(new[] { "location" }),
                        ["additionalProperties"] = JsonSerializer.SerializeToElement(false),
                    }),
                }),
            ]
        };

        var message = await client.Messages.Create(parameters);
        Console.WriteLine(message);
    }
}
package main

import (
	"context"
	"fmt"
	"log"

	"github.com/anthropics/anthropic-sdk-go"
)

func main() {
	client := anthropic.NewClient()

	response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
		Model:     anthropic.ModelClaudeOpus4_6,
		MaxTokens: 1024,
		Messages: []anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock("What's the weather like in San Francisco?")),
		},
		Tools: []anthropic.ToolUnionParam{
			{OfTool: &anthropic.ToolParam{
				Name:        "get_weather",
				Description: anthropic.String("Get the current weather in a given location"),
				Strict:      anthropic.Bool(true),
				InputSchema: anthropic.ToolInputSchemaParam{
					Properties: map[string]any{
						"location": map[string]any{
							"type":        "string",
							"description": "The city and state, e.g. San Francisco, CA",
						},
						"unit": map[string]any{
							"type": "string",
							"enum": []string{"celsius", "fahrenheit"},
						},
					},
					Required: []string{"location"},
					ExtraFields: map[string]any{
						"additionalProperties": false,
					},
				}}},
		},
	})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(response.Content)
}
import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;
import com.anthropic.models.messages.Tool;
import com.anthropic.models.messages.Tool.InputSchema;
import java.util.List;
import java.util.Map;

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

    InputSchema schema = InputSchema.builder()
        .properties(
            JsonValue.from(
                Map.of(
                    "location", Map.of(
                        "type", "string",
                        "description", "The city and state, e.g. San Francisco, CA"
                    ),
                    "unit", Map.of(
                        "type", "string",
                        "enum", List.of("celsius", "fahrenheit")
                    )
                )
            )
        )
        .putAdditionalProperty("required", JsonValue.from(List.of("location")))
        .putAdditionalProperty("additionalProperties", JsonValue.from(false))
        .build();

    MessageCreateParams params = MessageCreateParams.builder()
        .model(Model.CLAUDE_OPUS_4_6)
        .maxTokens(1024L)
        .addUserMessage("What's the weather like in San Francisco?")
        .addTool(
            Tool.builder()
                .name("get_weather")
                .description("Get the current weather in a given location")
                .strict(true)
                .inputSchema(schema)
                .build()
        )
        .build();

    Message response = client.messages().create(params);
    IO.println(response.content());
}
<?php

use Anthropic\Client;

$client = new Client(apiKey: getenv("ANTHROPIC_API_KEY"));

$message = $client->messages->create(
    maxTokens: 1024,
    messages: [
        ['role' => 'user', 'content' => "What's the weather like in San Francisco?"]
    ],
    model: 'claude-opus-4-6',
    tools: [
        [
            'name' => 'get_weather',
            'description' => 'Get the current weather in a given location',
            'strict' => true,
            'input_schema' => [
                'type' => 'object',
                'properties' => [
                    'location' => [
                        'type' => 'string',
                        'description' => 'The city and state, e.g. San Francisco, CA'
                    ],
                    'unit' => [
                        'type' => 'string',
                        'enum' => ['celsius', 'fahrenheit']
                    ]
                ],
                'required' => ['location'],
                'additionalProperties' => false
            ]
        ]
    ],
);

echo $message;
require "anthropic"

client = Anthropic::Client.new

message = client.messages.create(
  model: "claude-opus-4-6",
  max_tokens: 1024,
  messages: [
    { role: "user", content: "What's the weather like in San Francisco?" }
  ],
  tools: [
    {
      name: "get_weather",
      description: "Get the current weather in a given location",
      strict: true,
      input_schema: {
        type: "object",
        properties: {
          location: {
            type: "string",
            description: "The city and state, e.g. San Francisco, CA"
          },
          unit: {
            type: "string",
            enum: ["celsius", "fahrenheit"]
          }
        },
        required: ["location"],
        additionalProperties: false
      }
    }
  ]
)
puts message.content

Response format: Tool use blocks with validated inputs in response.content[x].input

{
  "type": "tool_use",
  "name": "get_weather",
  "input": {
    "location": "San Francisco, CA"
  }
}

Guarantees:

  • Tool input strictly follows the input_schema
  • Tool name is always valid (from provided tools or server tools)

How it works#

Create a JSON schema for your tool’s input_schema. The schema uses standard JSON Schema format with some limitations (see JSON Schema limitations). Set "strict": true as a top-level property in your tool definition, alongside name, description, and input_schema. When Claude uses the tool, the input field in the tool_use block will strictly follow your input_schema, and the name will always be valid.

Common use cases#

Validated tool inputs

Ensure tool parameters exactly match your schema:

from anthropic import Anthropic

client = Anthropic()
response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": "Search for flights to Tokyo departing June 1, 2026",
        }
    ],
    tools=[
        {
            "name": "search_flights",
            "strict": True,
            "input_schema": {
                "type": "object",
                "properties": {
                    "destination": {"type": "string"},
                    "departure_date": {"type": "string", "format": "date"},
                    "passengers": {
                        "type": "integer",
                        "enum": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
                    },
                },
                "required": ["destination", "departure_date"],
                "additionalProperties": False,
            },
        }
    ],
)

print(response)

const client = new Anthropic();

const searchFlightsTool: Anthropic.Tool = {
  name: "search_flights",
  strict: true,
  input_schema: {
    type: "object",
    properties: {
      destination: { type: "string" },
      departure_date: { type: "string", format: "date" },
      passengers: { type: "integer", enum: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] }
    },
    required: ["destination", "departure_date"],
    additionalProperties: false
  }
};

const response = await client.messages.create({
  model: "claude-opus-4-6",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Search for flights to Tokyo departing June 1, 2026" }],
  tools: [searchFlightsTool]
});

console.log(response);
using System;
using System.Text.Json;
using System.Threading.Tasks;
using Anthropic;
using Anthropic.Models.Messages;

class Program
{
    static async Task Main(string[] args)
    {
        AnthropicClient client = new()
        {
            ApiKey = Environment.GetEnvironmentVariable("ANTHROPIC_API_KEY")
        };

        var parameters = new MessageCreateParams
        {
            Model = Model.ClaudeOpus4_6,
            MaxTokens = 1024,
            Messages = [new() { Role = Role.User, Content = "Search for flights to Tokyo departing June 1, 2026" }],
            Tools = [
                new ToolUnion(new Tool()
                {
                    Name = "search_flights",
                    Strict = true,
                    InputSchema = new InputSchema(new Dictionary<string, JsonElement>
                    {
                        ["properties"] = JsonSerializer.SerializeToElement(new Dictionary<string, object>
                        {
                            ["destination"] = new { type = "string" },
                            ["departure_date"] = new { type = "string", format = "date" },
                            ["passengers"] = new { type = "integer", @enum = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 } },
                        }),
                        ["required"] = JsonSerializer.SerializeToElement(new[] { "destination", "departure_date" }),
                        ["additionalProperties"] = JsonSerializer.SerializeToElement(false),
                    }),
                }),
            ]
        };

        var message = await client.Messages.Create(parameters);
        Console.WriteLine(message);
    }
}
package main

import (
	"context"
	"fmt"
	"log"

	"github.com/anthropics/anthropic-sdk-go"
)

func main() {
	client := anthropic.NewClient()

	response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
		Model:     anthropic.ModelClaudeOpus4_6,
		MaxTokens: 1024,
		Messages: []anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock("Search for flights to Tokyo departing June 1, 2026")),
		},
		Tools: []anthropic.ToolUnionParam{
			{OfTool: &anthropic.ToolParam{
				Name:   "search_flights",
				Strict: anthropic.Bool(true),
				InputSchema: anthropic.ToolInputSchemaParam{
					Properties: map[string]any{
						"destination": map[string]any{
							"type": "string",
						},
						"departure_date": map[string]any{
							"type":   "string",
							"format": "date",
						},
						"passengers": map[string]any{
							"type": "integer",
							"enum": []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
						},
					},
					Required: []string{"destination", "departure_date"},
					ExtraFields: map[string]any{
						"additionalProperties": false,
					},
				}}},
		},
	})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(response)
}
import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;
import com.anthropic.models.messages.Tool;
import com.anthropic.models.messages.Tool.InputSchema;
import java.util.List;
import java.util.Map;

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

    InputSchema schema = InputSchema.builder()
        .properties(
            JsonValue.from(
                Map.of(
                    "destination", Map.of("type", "string"),
                    "departure_date", Map.of("type", "string", "format", "date"),
                    "passengers", Map.of(
                        "type", "integer",
                        "enum", List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
                    )
                )
            )
        )
        .putAdditionalProperty("required", JsonValue.from(List.of("destination", "departure_date")))
        .putAdditionalProperty("additionalProperties", JsonValue.from(false))
        .build();

    MessageCreateParams params = MessageCreateParams.builder()
        .model(Model.CLAUDE_OPUS_4_6)
        .maxTokens(1024L)
        .addUserMessage("Search for flights to Tokyo departing June 1, 2026")
        .addTool(
            Tool.builder()
                .name("search_flights")
                .strict(true)
                .inputSchema(schema)
                .build()
        )
        .build();

    Message response = client.messages().create(params);
    IO.println(response);
}
<?php

use Anthropic\Client;

$client = new Client(apiKey: getenv("ANTHROPIC_API_KEY"));

$message = $client->messages->create(
    maxTokens: 1024,
    messages: [
        ['role' => 'user', 'content' => 'Search for flights to Tokyo departing June 1, 2026']
    ],
    model: 'claude-opus-4-6',
    tools: [
        [
            'name' => 'search_flights',
            'strict' => true,
            'input_schema' => [
                'type' => 'object',
                'properties' => [
                    'destination' => ['type' => 'string'],
                    'departure_date' => ['type' => 'string', 'format' => 'date'],
                    'passengers' => [
                        'type' => 'integer',
                        'enum' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
                    ]
                ],
                'required' => ['destination', 'departure_date'],
                'additionalProperties' => false
            ]
        ]
    ],
);
require "anthropic"

client = Anthropic::Client.new

message = client.messages.create(
  model: "claude-opus-4-6",
  max_tokens: 1024,
  messages: [
    { role: "user", content: "Search for flights to Tokyo departing June 1, 2026" }
  ],
  tools: [
    {
      name: "search_flights",
      strict: true,
      input_schema: {
        type: "object",
        properties: {
          destination: { type: "string" },
          departure_date: { type: "string", format: "date" },
          passengers: {
            type: "integer",
            enum: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
          }
        },
        required: ["destination", "departure_date"],
        additionalProperties: false
      }
    }
  ]
)
puts message
Agentic workflow with multiple validated tools

Build reliable multi-step agents with guaranteed tool parameters:

from anthropic import Anthropic

client = Anthropic()
response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": "Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026",
        }
    ],
    tools=[
        {
            "name": "search_flights",
            "strict": True,
            "input_schema": {
                "type": "object",
                "properties": {
                    "origin": {"type": "string"},
                    "destination": {"type": "string"},
                    "departure_date": {"type": "string", "format": "date"},
                    "travelers": {"type": "integer", "enum": [1, 2, 3, 4, 5, 6]},
                },
                "required": ["origin", "destination", "departure_date"],
                "additionalProperties": False,
            },
        },
        {
            "name": "search_hotels",
            "strict": True,
            "input_schema": {
                "type": "object",
                "properties": {
                    "city": {"type": "string"},
                    "check_in": {"type": "string", "format": "date"},
                    "guests": {"type": "integer", "enum": [1, 2, 3, 4]},
                },
                "required": ["city", "check_in"],
                "additionalProperties": False,
            },
        },
    ],
)

print(response)

const client = new Anthropic();

const tools: Anthropic.Tool[] = [
  {
    name: "search_flights",
    strict: true,
    input_schema: {
      type: "object",
      properties: {
        origin: { type: "string" },
        destination: { type: "string" },
        departure_date: { type: "string", format: "date" },
        travelers: { type: "integer", enum: [1, 2, 3, 4, 5, 6] }
      },
      required: ["origin", "destination", "departure_date"],
      additionalProperties: false
    }
  },
  {
    name: "search_hotels",
    strict: true,
    input_schema: {
      type: "object",
      properties: {
        city: { type: "string" },
        check_in: { type: "string", format: "date" },
        guests: { type: "integer", enum: [1, 2, 3, 4] }
      },
      required: ["city", "check_in"],
      additionalProperties: false
    }
  }
];

const response = await client.messages.create({
  model: "claude-opus-4-6",
  max_tokens: 1024,
  messages: [
    {
      role: "user",
      content:
        "Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026"
    }
  ],
  tools: tools
});

console.log(response);
using System.Text.Json;
using Anthropic;
using Anthropic.Models.Messages;

class Program
{
    static async Task Main(string[] args)
    {
        AnthropicClient client = new();

        var parameters = new MessageCreateParams
        {
            Model = Model.ClaudeOpus4_6,
            MaxTokens = 1024,
            Messages = [new() { Role = Role.User, Content = "Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026" }],
            Tools = [
                new ToolUnion(new Tool()
                {
                    Name = "search_flights",
                    Strict = true,
                    InputSchema = new InputSchema(new Dictionary<string, JsonElement>
                    {
                        ["properties"] = JsonSerializer.SerializeToElement(new Dictionary<string, object>
                        {
                            ["origin"] = new { type = "string" },
                            ["destination"] = new { type = "string" },
                            ["departure_date"] = new { type = "string", format = "date" },
                            ["travelers"] = new { type = "integer", @enum = new[] { 1, 2, 3, 4, 5, 6 } },
                        }),
                        ["required"] = JsonSerializer.SerializeToElement(new[] { "origin", "destination", "departure_date" }),
                        ["additionalProperties"] = JsonSerializer.SerializeToElement(false),
                    }),
                }),
                new ToolUnion(new Tool()
                {
                    Name = "search_hotels",
                    Strict = true,
                    InputSchema = new InputSchema(new Dictionary<string, JsonElement>
                    {
                        ["properties"] = JsonSerializer.SerializeToElement(new Dictionary<string, object>
                        {
                            ["city"] = new { type = "string" },
                            ["check_in"] = new { type = "string", format = "date" },
                            ["guests"] = new { type = "integer", @enum = new[] { 1, 2, 3, 4 } },
                        }),
                        ["required"] = JsonSerializer.SerializeToElement(new[] { "city", "check_in" }),
                        ["additionalProperties"] = JsonSerializer.SerializeToElement(false),
                    }),
                }),
            ]
        };

        var message = await client.Messages.Create(parameters);
        Console.WriteLine(message);
    }
}
package main

import (
	"context"
	"fmt"
	"log"

	"github.com/anthropics/anthropic-sdk-go"
)

func main() {
	client := anthropic.NewClient()

	response, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
		Model:     anthropic.ModelClaudeOpus4_6,
		MaxTokens: 1024,
		Messages: []anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock("Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026")),
		},
		Tools: []anthropic.ToolUnionParam{
			{OfTool: &anthropic.ToolParam{
				Name:   "search_flights",
				Strict: anthropic.Bool(true),
				InputSchema: anthropic.ToolInputSchemaParam{
					Properties: map[string]any{
						"origin":         map[string]any{"type": "string"},
						"destination":    map[string]any{"type": "string"},
						"departure_date": map[string]any{"type": "string", "format": "date"},
						"travelers":      map[string]any{"type": "integer", "enum": []int{1, 2, 3, 4, 5, 6}},
					},
					Required: []string{"origin", "destination", "departure_date"},
					ExtraFields: map[string]any{
						"additionalProperties": false,
					},
				}}},
			{OfTool: &anthropic.ToolParam{
				Name:   "search_hotels",
				Strict: anthropic.Bool(true),
				InputSchema: anthropic.ToolInputSchemaParam{
					Properties: map[string]any{
						"city":     map[string]any{"type": "string"},
						"check_in": map[string]any{"type": "string", "format": "date"},
						"guests":   map[string]any{"type": "integer", "enum": []int{1, 2, 3, 4}},
					},
					Required: []string{"city", "check_in"},
					ExtraFields: map[string]any{
						"additionalProperties": false,
					},
				}}},
		},
	})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(response)
}
import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;
import com.anthropic.models.messages.Tool;
import com.anthropic.models.messages.Tool.InputSchema;
import java.util.List;
import java.util.Map;

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

    InputSchema flightsSchema = InputSchema.builder()
        .properties(
            JsonValue.from(
                Map.of(
                    "origin", Map.of("type", "string"),
                    "destination", Map.of("type", "string"),
                    "departure_date", Map.of("type", "string", "format", "date"),
                    "travelers", Map.of("type", "integer", "enum", List.of(1, 2, 3, 4, 5, 6))
                )
            )
        )
        .putAdditionalProperty("required", JsonValue.from(List.of("origin", "destination", "departure_date")))
        .putAdditionalProperty("additionalProperties", JsonValue.from(false))
        .build();

    InputSchema hotelsSchema = InputSchema.builder()
        .properties(
            JsonValue.from(
                Map.of(
                    "city", Map.of("type", "string"),
                    "check_in", Map.of("type", "string", "format", "date"),
                    "guests", Map.of("type", "integer", "enum", List.of(1, 2, 3, 4))
                )
            )
        )
        .putAdditionalProperty("required", JsonValue.from(List.of("city", "check_in")))
        .putAdditionalProperty("additionalProperties", JsonValue.from(false))
        .build();

    MessageCreateParams params = MessageCreateParams.builder()
        .model(Model.CLAUDE_OPUS_4_6)
        .maxTokens(1024L)
        .addUserMessage("Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026")
        .addTool(
            Tool.builder()
                .name("search_flights")
                .strict(true)
                .inputSchema(flightsSchema)
                .build()
        )
        .addTool(
            Tool.builder()
                .name("search_hotels")
                .strict(true)
                .inputSchema(hotelsSchema)
                .build()
        )
        .build();

    Message response = client.messages().create(params);
    IO.println(response);
}
<?php

use Anthropic\Client;

$client = new Client(apiKey: getenv("ANTHROPIC_API_KEY"));

$message = $client->messages->create(
    maxTokens: 1024,
    messages: [
        ['role' => 'user', 'content' => 'Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026']
    ],
    model: 'claude-opus-4-6',
    tools: [
        [
            'name' => 'search_flights',
            'strict' => true,
            'input_schema' => [
                'type' => 'object',
                'properties' => [
                    'origin' => ['type' => 'string'],
                    'destination' => ['type' => 'string'],
                    'departure_date' => ['type' => 'string', 'format' => 'date'],
                    'travelers' => ['type' => 'integer', 'enum' => [1, 2, 3, 4, 5, 6]]
                ],
                'required' => ['origin', 'destination', 'departure_date'],
                'additionalProperties' => false
            ]
        ],
        [
            'name' => 'search_hotels',
            'strict' => true,
            'input_schema' => [
                'type' => 'object',
                'properties' => [
                    'city' => ['type' => 'string'],
                    'check_in' => ['type' => 'string', 'format' => 'date'],
                    'guests' => ['type' => 'integer', 'enum' => [1, 2, 3, 4]]
                ],
                'required' => ['city', 'check_in'],
                'additionalProperties' => false
            ]
        ]
    ],
);

echo $message->content[0]->text;
require "anthropic"

client = Anthropic::Client.new

message = client.messages.create(
  model: "claude-opus-4-6",
  max_tokens: 1024,
  messages: [
    { role: "user", content: "Help me plan a trip from New York to Paris for 2 people, departing June 1, 2026" }
  ],
  tools: [
    {
      name: "search_flights",
      strict: true,
      input_schema: {
        type: "object",
        properties: {
          origin: { type: "string" },
          destination: { type: "string" },
          departure_date: { type: "string", format: "date" },
          travelers: { type: "integer", enum: [1, 2, 3, 4, 5, 6] }
        },
        required: ["origin", "destination", "departure_date"],
        additionalProperties: false
      }
    },
    {
      name: "search_hotels",
      strict: true,
      input_schema: {
        type: "object",
        properties: {
          city: { type: "string" },
          check_in: { type: "string", format: "date" },
          guests: { type: "integer", enum: [1, 2, 3, 4] }
        },
        required: ["city", "check_in"],
        additionalProperties: false
      }
    }
  ]
)
puts message

Data retention#

Strict tool use compiles tool input_schema definitions into grammars using the same pipeline as structured outputs. Tool schemas are temporarily cached for up to 24 hours since last use. Prompts and responses are not retained beyond the API response.

Strict tool use is HIPAA eligible, but PHI must not be included in tool schema definitions. The API caches compiled schemas separately from message content, and these cached schemas do not receive the same PHI protections as prompts and responses. Do not include PHI in input_schema property names, enum values, const values, or pattern regular expressions. PHI should only appear in message content (prompts and responses), where it is protected under HIPAA safeguards.

For ZDR and HIPAA eligibility across all features, see API and data retention.

Link last verified June 7, 2026. View original ↗
Source: Anthropic Platform Docs
Link last verified: 2026-04-05