# Tool Use — Java

For conceptual overview (tool definitions, tool choice, tips), see [shared/tool-use-concepts.md](../../shared/tool-use-concepts.md).

## Tool Use (Beta)

The Java SDK supports beta tool use with annotated classes. Tool classes implement `Supplier<String>` for automatic execution via `BetaToolRunner`.

### Tool Runner (automatic loop)

```java
import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.beta.messages.BetaMessage;
import com.anthropic.helpers.BetaToolRunner;
import com.fasterxml.jackson.annotation.JsonClassDescription;
import com.fasterxml.jackson.annotation.JsonPropertyDescription;
import java.util.function.Supplier;

@JsonClassDescription("Get the weather in a given location")
static class GetWeather implements Supplier<String> {
    @JsonPropertyDescription("The city and state, e.g. San Francisco, CA")
    public String location;

    @Override
    public String get() {
        return "The weather in " + location + " is sunny and 72°F";
    }
}

BetaToolRunner toolRunner = client.beta().messages().toolRunner(
    MessageCreateParams.builder()
        .model("claude-opus-5")
        .maxTokens(16000L)
        .putAdditionalHeader("anthropic-beta", "structured-outputs-2025-11-13")
        .addTool(GetWeather.class)
        .addUserMessage("What's the weather in San Francisco?")
        .build());

for (BetaMessage message : toolRunner) {
    System.out.println(message);
}
```

### Memory Tool

The Java SDK provides `BetaMemoryToolHandler` for implementing the memory tool backend. You supply a handler that manages file storage, and the `BetaToolRunner` handles memory tool calls automatically.

```java
import com.anthropic.helpers.BetaMemoryToolHandler;
import com.anthropic.helpers.BetaToolRunner;
import com.anthropic.models.beta.messages.BetaMemoryTool20250818;
import com.anthropic.models.beta.messages.BetaMessage;
import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.beta.messages.ToolRunnerCreateParams;

// Implement BetaMemoryToolHandler with your storage backend (e.g., filesystem)
BetaMemoryToolHandler memoryHandler = new FileSystemMemoryToolHandler(sandboxRoot);

MessageCreateParams createParams = MessageCreateParams.builder()
    .model("claude-opus-5")
    .maxTokens(4096L)
    .addTool(BetaMemoryTool20250818.builder().build())
    .addUserMessage("Remember that my favorite color is blue")
    .build();

BetaToolRunner toolRunner = client.beta().messages().toolRunner(
    ToolRunnerCreateParams.builder()
        .betaMemoryToolHandler(memoryHandler)
        .initialMessageParams(createParams)
        .build());

for (BetaMessage message : toolRunner) {
    System.out.println(message);
}
```

See the [shared memory tool concepts](../../shared/tool-use-concepts.md) for more details on the memory tool.

### Non-Beta Tool Declaration (manual JSON schema)

`Tool.InputSchema.Properties` is a freeform `Map<String, JsonValue>` wrapper — build property schemas via `putAdditionalProperty`. `type: "object"` is the default. The builder has a direct `.addTool(Tool)` overload that wraps in `ToolUnion` automatically.

```java
import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.Tool;

Tool tool = Tool.builder()
    .name("get_weather")
    .description("Get the current weather in a given location")
    .inputSchema(Tool.InputSchema.builder()
        .properties(Tool.InputSchema.Properties.builder()
            .putAdditionalProperty("location", JsonValue.from(Map.of("type", "string")))
            .build())
        .required(List.of("location"))
        .build())
    .build();

MessageCreateParams params = MessageCreateParams.builder()
    .model(Model.CLAUDE_SONNET_4_6)
    .maxTokens(16000L)
    .addTool(tool)
    .addUserMessage("Weather in Paris?")
    .build();
```

For manual tool loops, handle `tool_use` blocks in the response, send `tool_result` back, loop until `stop_reason` is `"end_turn"`. See [shared tool use concepts](../../shared/tool-use-concepts.md).

### Building `MessageParam` with Content Blocks (Tool Result Round-Trip)

`MessageParam.Content` is an inner union class (string | list). Use the builder's `.contentOfBlockParams(List<ContentBlockParam>)` alias — there is NO separate `MessageParamContent` class with a static `ofBlockParams`:

```java
import com.anthropic.models.messages.MessageParam;
import com.anthropic.models.messages.ContentBlockParam;
import com.anthropic.models.messages.ToolResultBlockParam;

List<ContentBlockParam> results = List.of(
    ContentBlockParam.ofToolResult(ToolResultBlockParam.builder()
        .toolUseId(toolUseBlock.id())
        .content(yourResultString)
        .build())
);

MessageParam toolResultMsg = MessageParam.builder()
    .role(MessageParam.Role.USER)
    .contentOfBlockParams(results)   // builder alias for Content.ofBlockParams(...)
    .build();
```

---

## Structured Output

The class-based overload auto-derives the JSON schema from your POJO and gives you a typed `.text()` return — no manual schema, no manual parsing.

```java
import com.anthropic.models.messages.StructuredMessageCreateParams;

record Book(String title, String author) {}
record BookList(List<Book> books) {}

StructuredMessageCreateParams<BookList> params = MessageCreateParams.builder()
    .model(Model.CLAUDE_SONNET_4_6)
    .maxTokens(16000L)
    .outputConfig(BookList.class)  // returns a typed builder
    .addUserMessage("List 3 classic novels")
    .build();

client.messages().create(params).content().stream()
    .flatMap(cb -> cb.text().stream())
    .forEach(typed -> {
        // typed.text() returns BookList, not String
        for (Book b : typed.text().books()) System.out.println(b.title());
    });
```

Supports Jackson annotations: `@JsonPropertyDescription`, `@JsonIgnore`, `@ArraySchema(minItems=...)`. Manual schema path: `OutputConfig.builder().format(JsonOutputFormat.builder().schema(...).build())`.

---

## Anthropic-Defined Tools

Version-suffixed types; `name`/`type` auto-set by builder. Direct `.addTool()` overloads exist for most tool types; where one is missing (newer or less-common tools — see the advisor note below), wrap via the union type's static factory: `.addTool(BetaToolUnion.of<ToolName>(builder…build()))`. Web search and code execution are server-executed; bash and text editor are client-executed (you handle the `tool_use` locally — see `shared/tool-use-concepts.md`).

```java
import com.anthropic.models.messages.WebSearchTool20260209;
import com.anthropic.models.messages.ToolBash20250124;
import com.anthropic.models.messages.ToolTextEditor20250728;
import com.anthropic.models.messages.CodeExecutionTool20260120;

.addTool(WebSearchTool20260209.builder()
    .maxUses(5L)                              // optional
    .allowedDomains(List.of("example.com"))   // optional
    .build())
.addTool(ToolBash20250124.builder().build())
.addTool(ToolTextEditor20250728.builder().build())
.addTool(CodeExecutionTool20260120.builder().build())
```

Also available: `WebFetchTool20260209`, `MemoryTool20250818`, `ToolSearchToolBm25_20251119`. For the advisor tool, use `BetaAdvisorTool20260301` in the beta namespace with `.addBeta("advisor-tool-2026-03-01")` (server-side; advisor model ≥ executor model). There is no direct `.addTool(BetaAdvisorTool20260301)` overload on the beta builder — wrap it via the `BetaToolUnion` static factory for the advisor type; if `javac` rejects the specific factory method name, `javap com.anthropic.models.beta.messages.BetaToolUnion | grep -i advisor` shows the exact one.

### Beta namespace (MCP, compaction)

For beta-only features use `com.anthropic.models.beta.messages.*` — class names have a `Beta` prefix AND live in the beta package. The beta `MessageCreateParams.Builder` has direct `.addTool(BetaToolBash20250124)` overloads AND `.addMcpServer()`:

```java
import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.beta.messages.BetaToolBash20250124;
import com.anthropic.models.beta.messages.BetaCodeExecutionTool20260120;
import com.anthropic.models.beta.messages.BetaRequestMcpServerUrlDefinition;

MessageCreateParams params = MessageCreateParams.builder()
    .model(Model.CLAUDE_OPUS_4_8)
    .maxTokens(16000L)
    .addBeta("mcp-client-2025-11-20")
    .addTool(BetaToolBash20250124.builder().build())
    .addTool(BetaCodeExecutionTool20260120.builder().build())
    .addMcpServer(BetaRequestMcpServerUrlDefinition.builder()
        .name("my-server")
        .url("https://example.com/mcp")
        .build())
    .addUserMessage("...")
    .build();

client.beta().messages().create(params);
```

`BetaTool*` types are NOT interchangeable with non-beta `Tool*` — pick one namespace per request.

**Reading server-tool blocks in the response:** `ServerToolUseBlock` has `.id()`, `.name()` (enum), and `._input()` returning raw `JsonValue` — there is NO typed `.input()`. For code execution results, unwrap two levels:

```java
for (ContentBlock block : response.content()) {
    block.serverToolUse().ifPresent(stu -> {
        System.out.println("tool: " + stu.name() + " input: " + stu._input());
    });
    block.codeExecutionToolResult().ifPresent(r -> {
        r.content().resultBlock().ifPresent(result -> {
            System.out.println("stdout: " + result.stdout());
            System.out.println("stderr: " + result.stderr());
            System.out.println("exit: " + result.returnCode());
        });
    });
}
```

---

