Full example of programmatic tool calling

programmatic-tool-calling.ts

import Anthropic from "@anthropic-ai/sdk";
import { Pool } from "pg";

const anthropic = new Anthropic();

// dn connection - Claude never sees this
const db = new Pool({
  host: "your-database-host.com",
  port: 5432,
  database: "sales_db",
  user: "your_username",
  password: "your_secret_password",
});

const tools = [
  {
    type: "code_execution_20250825" as const,
    name: "code_execution",
  },
  {
    name: "query_database",
    description:
      "Execute a SQL query against the sales database. Returns a list of rows as JSON objects with fields: region (string), revenue (number), quarter (string).",
    input_schema: {
      type: "object" as const,
      properties: {
        sql: {
          type: "string",
          description: "SQL query to execute",
        },
      },
      required: ["sql"],
    },
    allowed_callers: ["code_execution_20250825" as const],
  },
];

async function executeQuery(sql: string): Promise<string> {
  try {
    const result = await db.query(sql);
    return JSON.stringify(result.rows);
  } catch (error) {
    return JSON.stringify({ error: error.message });
  }
}

async function chat(userMessage: string) {
  let messages: Anthropic.MessageParam[] = [
    { role: "user", content: userMessage },
  ];

  let containerId: string | undefined;

  while (true) {
    // ════════════════════════════════════════════════════════════════
    // API CALL - where Claude's Python code runs (or resumes)
    // ════════════════════════════════════════════════════════════════
    const response = await anthropic.beta.messages.create({
      model: "claude-sonnet-4-5",
      betas: ["advanced-tool-use-2025-11-20"],
      max_tokens: 4096,
      messages,
      tools,
      ...(containerId && { container: containerId }),
    });
    // ════════════════════════════════════════════════════════════════
    // At this point, Claude's code is either PAUSED or FINISHED
    // ════════════════════════════════════════════════════════════════

    if (response.container?.id) {
      containerId = response.container.id;
    }

    // Code FINISHED - Python script completed, Claude gives final answer
    if (response.stop_reason === "end_turn") {
      const textBlock = response.content.find((block) => block.type === "text");
      return textBlock?.type === "text" ? textBlock.text : "No response";
    }

    // Code PAUSED - waiting at an `await query_database(...)` call
    if (response.stop_reason === "tool_use") {
      messages.push({ role: "assistant", content: response.content });

      const toolResults: Anthropic.ToolResultBlockParam[] = [];

      for (const block of response.content) {
        if (block.type === "tool_use" && block.name === "query_database") {
          // Run query on YOUR infrastructure
          console.log(`Executing query: ${block.input.sql}`);
          const result = await executeQuery(block.input.sql as string);

          // This becomes the return value of the paused await
          toolResults.push({
            type: "tool_result",
            tool_use_id: block.id,
            content: result,
          });
        }
      }

      // Add results to messages - next API call will resume the code
      if (toolResults.length > 0) {
        messages.push({ role: "user", content: toolResults });
      }
    }
  }
}

chat(
  "Query sales data for West, East, and Central regions, then tell me which had the highest revenue"
).then(console.log);
```