OpenAI builtin tool web_search is not working in the createAgent

[arbazalam01]

Checked other resources

• This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/).
• I added a very descriptive title to this issue.
• I searched the LangChain.js documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain.js rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

import {
AgentState,
createAgent,
createMiddleware,
HumanMessage,
ToolNode,
} from "langchain";
import { ChatOpenAI } from "@langchain/openai";
const model = new ChatOpenAI({
modelName: "gpt-5-mini-2025-08-07",
apiKey: env.openai.apiKey,
});

const researcherAgent = createAgent({
llm: model,
tools: [{ name: "web_search", type: "web_search" }],
prompt: research_system_prompt(getTodayStr()),
});

Error Message and Stack Trace (if applicable)

throw new UnreachableNodeError(
^

UnreachableNodeError: Node tools is not reachable.

If you are returning Command objects from your node,
make sure you are passing names of potential destination nodes as an "ends" array
into ".addNode(..., { ends: ["node1", "node2"] })".

Description

I'm trying to use the openai built-in web search tool, but it's throwing an error

System Info

"@langchain/core": "1.0.0-alpha.5"

[pawel-twardziak]

hi @arbazalam01

there are to ways for binding tools:

• Option A: Use a real search Tool (recommended): Provide a LangChain Tool such as Tavily, SerpAPI, or Bing to createAgent. This gives the agent a concrete, invokable tool, so the tools node is reachable.

import { ChatOpenAI } from "@langchain/openai";
import { createAgent } from "langgraph/prebuilt"; // or your createAgent import
import { TavilySearchResults } from "@langchain/community/tools/tavily_search";

const model = new ChatOpenAI({ modelName: "gpt-4o-mini", temperature: 0 });
const tools = [new TavilySearchResults({ maxResults: 5 })];

const agent = createAgent({
  llm: model,
  tools, // real LangChain Tool(s)
  prompt: research_system_prompt(getTodayStr()),
});

• Option B: Use OpenAI built-in web_search without a ToolNode: Bind OpenAI’s built-in tool directly to the model so the search runs server-side during the model call. Then pass no external tools to createAgent so no tools node is created.

import { ChatOpenAI } from "@langchain/openai";
import { createAgent } from "langgraph/prebuilt"; // or your createAgent import

// Use a model that supports the web_search built-in
const modelWithSearch = new ChatOpenAI({
  modelName: "gpt-5-mini-2025-08-07",
  temperature: 0,
}).bind({
  tools: [{ type: "web_search" }],
  tool_choice: "auto",
});

const agent = createAgent({
  llm: modelWithSearch,
  tools: [], // no external ToolNode; prevents unreachable tools node
  prompt: research_system_prompt(getTodayStr()),
});

[hntrl]

Believe this was fixed in #9074