Claude API Fine-Grained Tool Streaming実践ガイド — ツール呼び出しのレイテンシを最大80%削減する実装パターン

(15秒待機)
Chunk 1: '{"'
Chunk 2: 'query": "Ty'
Chunk 3: 'peScri'
Chunk 4: 'pt 5.0 5.1 '
Chunk 5: '5.2 5'
Chunk 6: '.3'
Chunk 7: ' new f'
Chunk 8: 'eatur'
...

(3秒待機)
Chunk 1: '{"query": "TypeScript 5.0 5.1 5.2 5.3'
Chunk 2: ' new features comparison'

import Anthropic from "@anthropic-ai/sdk";

const anthropic = new Anthropic();

const stream = anthropic.messages.stream({
  model: "claude-opus-4-6",
  max_tokens: 65536,
  tools: [
    {
      name: "make_file",
      description: "Write text to a file",
      eager_input_streaming: true,  // これだけ
      input_schema: {
        type: "object",
        properties: {
          filename: {
            type: "string",
            description: "The filename to write text to",
          },
          lines_of_text: {
            type: "array",
            description: "An array of lines of text to write to the file",
          },
        },
        required: ["filename", "lines_of_text"],
      },
    },
  ],
  messages: [
    {
      role: "user",
      content: "Can you write a long poem and make a file called poem.txt?",
    },
  ],
});

const message = await stream.finalMessage();
console.log(message.usage);

import Anthropic from "@anthropic-ai/sdk";

const anthropic = new Anthropic();

const stream = anthropic.messages.stream({
  model: "claude-opus-4-6",
  max_tokens: 65536,
  tools: [
    {
      name: "write_code",
      description: "Write code to a file",
      eager_input_streaming: true,
      input_schema: {
        type: "object",
        properties: {
          filename: { type: "string" },
          code: { type: "string", description: "The source code" },
        },
        required: ["filename", "code"],
      },
    },
  ],
  messages: [{ role: "user", content: "Write a Express.js server" }],
});

let accumulatedJson = "";

stream.on("inputJson", (json, snapshot) => {
  // json: 今回の差分文字列
  // snapshot: 蓄積済み文字列全体
  accumulatedJson = snapshot;

  // リアルタイムにUIへ反映したい場合は
  // 部分パースを試みる
  try {
    const partial = JSON.parse(snapshot);
    if (partial.code) {
      process.stdout.write(partial.code.slice(-50)); // 末尾を表示
    }
  } catch {
    // まだ不完全なJSON — 無視して蓄積を続ける
  }
});

stream.on("message", (message) => {
  // 完了後、最終的なメッセージから完全なtool_useを取得
  for (const block of message.content) {
    if (block.type === "tool_use") {
      console.log("Final input:", block.input);
    }
  }
});

await stream.finalMessage();

npm install partial-json-parser

import { parse } from "partial-json-parser";

stream.on("inputJson", (json, snapshot) => {
  // 不完全なJSONでもパース可能な部分まで解釈してくれる
  const partial = parse(snapshot);
  if (partial.code) {
    renderCodePreview(partial.code);
  }
});

stream.on("message", (message) => {
  if (message.stop_reason === "max_tokens") {
    // パラメータが途中で切れている可能性が高い
    console.warn("max_tokens reached — tool input may be incomplete");
    // リトライするか、ユーザーに通知する
    return;
  }

  for (const block of message.content) {
    if (block.type === "tool_use") {
      // stop_reason が "tool_use" なら正常完了
      const input = block.input;
      await executeTool(block.name, input);
    }
  }
});

// 不正なJSONを安全にモデルへ返す
const toolResult = {
  type: "tool_result" as const,
  tool_use_id: toolUseBlock.id,
  is_error: true,
  content: JSON.stringify({
    INVALID_JSON: invalidJsonString.replace(/"/g, '\\"'),
  }),
};