How to output structured JSON from DuckDuckGo tool call

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Example Code

import dotenv from 'dotenv';
import { z } from 'zod';
import { DuckDuckGoSearch } from "@langchain/community/tools/duckduckgo_search";
import { ChatPromptTemplate } from "@langchain/core/prompts";
import { RunnableLambda } from "@langchain/core/runnables";
import { HumanMessage } from "@langchain/core/messages";
import { ChatOpenAI } from "@langchain/openai";


dotenv.config();

const resultsSchema = z.object({
  results: z.array(
    z.object({
      websiteName: z.string(),
      price: z.string(),
      link: z.string(),
    })
  ),
});

const llm = new ChatOpenAI({
  model: "gpt-4",
  temperature: 0,
})

const tool = new DuckDuckGoSearch({ maxResults: 10 });

const prompt = ChatPromptTemplate.fromMessages([
    ["system", "Your task is to list all prices in format Website Name - Price - link. Nothing else"],
    ["placeholder", "{messages}"],
  ]);

  const llmWithTools = llm.bindTools([tool]);
  
  const chain = prompt.pipe(llmWithTools).pipe(jsonOutput);
  
  const toolChain = RunnableLambda.from(async (userInput, config) => {
    const humanMessage = new HumanMessage(userInput);
    const aiMsg = await chain.invoke(
      {
        messages: [new HumanMessage(userInput)],
      },
      config
    );
    const toolMsgs = await tool.batch(aiMsg.tool_calls, config);
    console.log("TOOL",toolMsgs);
    return chain.with.invoke(
      {
        messages: [humanMessage, aiMsg, ...toolMsgs],
      },
      config
    );
  });

  const postReqMessage = "Fender Straticaster";
  
  const toolChainResult = await toolChain.invoke(
    `${postReqMessage} list all current prices`
  );
  console.log("TOOLCHAIN RESULT", toolChainResult);
  const { content } = toolChainResult;

  console.log(
    "AIMessage",
    JSON.stringify(
      {
        tool_calls,
        content,
      },
      null,
      2
    )
  );

Description

I am using an example from official documentation here: duckduckgo_search
The output is a string, but I want it to be a structured JSON
When trying to add method withStructuredJson()
I got error, that basically says that bindTools method doesnt exist on the object
Who knows how to achieve a structured output after calling DuckDuckGo tool
Please help, or point to a working similar solution
Thank you

System Info

{
"type": "module",
"dependencies": {
"@langchain/community": "^0.3.24",
"@langchain/core": "^0.3.30",
"@langchain/openai": "^0.3.17",
"dotenv": "^16.4.7",
"duck-duck-scrape": "^2.2.7",
"langchain": "^0.3.11",
"zod": "^3.24.1"
}
}