Notice that in the above examples the agent did some extra work after querying the RetrievalQAChain. You can avoid that and just return the result directly.
tools = [
    Tool(
        name = "State of Union QA System",
        func=state_of_union.run,
        description="useful for when you need to answer questions about the most recent state of the union address. Input should be a fully formed question.",
        return_direct=True
    ),
    Tool(
        name = "Ruff QA System",
        func=ruff.run,
        description="useful for when you need to answer questions about ruff (a python linter). Input should be a fully formed question.",
        return_direct=True
    ),
]
agent = initialize_agent(tools, llm, agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION, verbose=True)
agent.run("What did biden say about ketanji brown jackson in the state of the union address?")
> Entering new AgentExecutor chain...
 I need to find out what Biden said about Ketanji Brown Jackson in the State of the Union address.
Action: State of Union QA System
Action Input: What did Biden say about Ketanji Brown Jackson in the State of the Union address?
Observation:  Biden said that Jackson is one of the nation's top legal minds and that she will continue Justice Breyer's legacy of excellence.
> Finished chain.
" Biden said that Jackson is one of the nation's top legal minds and that she will continue Justice Breyer's legacy of excellence."
agent.run("Why use ruff over flake8?")
> Entering new AgentExecutor chain...
 I need to find out the advantages of using ruff over flake8
Action: Ruff QA System
rtdocs_stable/api.python.langchain.com/en/stable/modules/agents/agent_executors/examples/agent_vectorstore.html