In rag tutorial part 2, how can graph_builder decide whether to call tool or not ?

[astrung]

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Example Code

    from langgraph.graph import END
    from langgraph.prebuilt import ToolNode, tools_condition

    graph_builder.add_node(query_or_respond)
    graph_builder.add_node(tools)
    graph_builder.add_node(generate)

    graph_builder.set_entry_point("query_or_respond")
    graph_builder.add_conditional_edges(
        "query_or_respond",
        tools_condition,
        {END: END, "tools": "tools"},
    )
    graph_builder.add_edge("tools", "generate")
    graph_builder.add_edge("generate", END)

    graph = graph_builder.compile()

Description

In this tutorial: https://python.langchain.com/docs/tutorials/qa_chat_history/, I don't see any code lines for implementing logic to decide whether running tool(retrieve relevant document related to a query) or not.

So how this RAG app can decide whether running tool or not ? and it decide based on what logic ? I am a newbie to LLM so please explain it to me. Above lines is example codes from this tutorial:

System Info

Windows 11, langchain 0.3.44

[astrung]

hello. can anyone help me ?