Build Multi-Agent Systems

Guide the user through building multiple AI agents that collaborate — a supervisor delegates tasks, specialists handle their domains, and results flow back. Uses DSPy for each agent's reasoning and LangGraph for orchestration, handoff, and parallel execution.

Step 1: Identify the agents

Ask the user:

1. What's the overall task? (research a topic, handle support, create content, analyze data?)
2. What specialist roles do you need? (researcher, writer, reviewer, analyst, etc.)
3. How do agents hand off work? (supervisor routes, chain passes forward, parallel fan-out?)
4. Do any agents need tools? (search, database, APIs, code execution?)

Common multi-agent patterns

Step 2: Build each agent as a DSPy module

Each agent gets its own signature, reasoning strategy, and (optionally) tools.

Simple agent — just a DSPy module

import dspy

class ResearchSummary(dspy.Signature):
    """Research the topic and provide a detailed summary with key findings."""
    topic: str = dspy.InputField()
    sources: list[str] = dspy.InputField(desc="Search results or documents to analyze")
    summary: str = dspy.OutputField(desc="Detailed research summary")
    key_findings: list[str] = dspy.OutputField(desc="Top 3-5 key findings")

class ResearchAgent(dspy.Module):
    def __init__(self, retriever):
        self.retriever = retriever
        self.analyze = dspy.ChainOfThought(ResearchSummary)

    def forward(self, topic):
        sources = self.retriever(topic).passages
        return self.analyze(topic=topic, sources=sources)

Agent with tools — use ReAct

def search_web(query: str) -> str:
    """Search the web for current information."""
    # your search implementation
    return results

def query_database(sql: str) -> str:
    """Query the analytics database."""
    # your database implementation
    return results

class DataAnalyst(dspy.Module):
    def __init__(self):
        self.agent = dspy.ReAct(
            "question, context -> analysis, recommendation",
            tools=[search_web, query_database],
            max_iters=5,
        )

    def forward(self, question, context=""):
        return self.agent(question=question, context=context)

Agent with LangChain tools

Convert pre-built LangChain tools for use in DSPy agents:

from langchain_community.tools import DuckDuckGoSearchRun

search_tool = dspy.Tool.from_langchain(DuckDuckGoSearchRun())

class WebResearcher(dspy.Module):
    def __init__(self):
        self.agent = dspy.ReAct(
            "question -> findings",
            tools=[search_tool],
            max_iters=5,
        )

    def forward(self, question):
        return self.agent(question=question)

Step 3: Add a supervisor (LangGraph)

The supervisor decides which agent to call next based on the current state.

Define the shared state

from langgraph.graph import StateGraph, START, END
from typing import TypedDict, Annotated
import operator

class TeamState(TypedDict):
    task: str                                     # the overall task
    messages: Annotated[list[dict], operator.add]  # communication log
    current_agent: str                             # who's working now
    results: dict                                  # collected results from agents
    status: str                                    # "in_progress", "done", "needs_review"

Build the supervisor

class RouteTask(dspy.Signature):
    """Decide which specialist agent should handle the next step."""
    task: str = dspy.InputField(desc="The overall task")
    completed_work: str = dspy.InputField(desc="Work completed so far")
    available_agents: list[str] = dspy.InputField()
    next_agent: str = dspy.OutputField(desc="Which agent to call next")
    sub_task: str = dspy.OutputField(desc="Specific instruction for that agent")
    is_complete: bool = dspy.OutputField(desc="Whether the overall task is done")

supervisor_module = dspy.ChainOfThought(RouteTask)

def supervisor(state: TeamState) -> dict:
    completed = "\n".join(
        f"{k}: {v}" for k, v in state["results"].items()
    )
    result = supervisor_module(
        task=state["task"],
        completed_work=completed or "Nothing yet",
        available_agents=["researcher", "writer", "reviewer"],
    )

    if result.is_complete:
        return {"status": "done", "current_agent": "none"}

    return {
        "current_agent": result.next_agent,
        "messages": [{"role": "supervisor", "content": f"@{result.next_agent}: {result.sub_task}"}],
    }

Wire up the agents as graph nodes

researcher = ResearchAgent(retriever=my_retriever)
writer_module = dspy.ChainOfThought(WriteContent)
reviewer_module = dspy.ChainOfThought(ReviewContent)

def researcher_node(state: TeamState) -> dict:
    task_msg = state["messages"][-1]["content"]
    result = researcher(topic=task_msg)
    return {
        "results": {**state["results"], "research": result.summary},
        "messages": [{"role": "researcher", "content": result.summary}],
    }

def writer_node(state: TeamState) -> dict:
    result = writer_module(
        task=state["task"],
        research=state["results"].get("research", ""),
    )
    return {
        "results": {**state["results"], "draft": result.output},
        "messages": [{"role": "writer", "content": result.output}],
    }

def reviewer_node(state: TeamState) -> dict:
    result = reviewer_module(
        draft=state["results"].get("draft", ""),
        task=state["task"],
    )
    return {
        "results": {**state["results"], "review": result.feedback},
        "messages": [{"role": "reviewer", "content": result.feedback}],
    }

Build the graph

graph = StateGraph(TeamState)

# Add nodes
graph.add_node("supervisor", supervisor)
graph.add_node("researcher", researcher_node)
graph.add_node("writer", writer_node)
graph.add_node("reviewer", reviewer_node)

# Supervisor decides who goes next
graph.add_edge(START, "supervisor")

def route_to_agent(state: TeamState) -> str:
    if state["status"] == "done":
        return "done"
    return state["current_agent"]

graph.add_conditional_edges(
    "supervisor",
    route_to_agent,
    {
        "researcher": "researcher",
        "writer": "writer",
        "reviewer": "reviewer",
        "done": END,
    },
)

# All agents report back to supervisor
graph.add_edge("researcher", "supervisor")
graph.add_edge("writer", "supervisor")
graph.add_edge("reviewer", "supervisor")

app = graph.compile()

Run it

result = app.invoke({
    "task": "Write a blog post about the benefits of remote work",
    "messages": [],
    "current_agent": "",
    "results": {},
    "status": "in_progress",
})
# Supervisor routes: researcher → writer → reviewer → done
print(result["results"]["draft"])

Step 4: Agent handoff pattern

When one agent passes work directly to another (no supervisor).

Shared context via state

class HandoffState(TypedDict):
    task: str
    context: Annotated[list[str], operator.add]  # accumulated context
    output: str

def agent_a(state: HandoffState) -> dict:
    result = module_a(task=state["task"])
    return {"context": [f"Agent A found: {result.output}"]}

def agent_b(state: HandoffState) -> dict:
    full_context = "\n".join(state["context"])
    result = module_b(task=state["task"], context=full_context)
    return {"context": [f"Agent B added: {result.output}"]}

def agent_c(state: HandoffState) -> dict:
    full_context = "\n".join(state["context"])
    result = module_c(task=state["task"], context=full_context)
    return {"output": result.output}

graph = StateGraph(HandoffState)
graph.add_node("a", agent_a)
graph.add_node("b", agent_b)
graph.add_node("c", agent_c)
graph.add_edge(START, "a")
graph.add_edge("a", "b")
graph.add_edge("b", "c")
graph.add_edge("c", END)

Conditional handoff

Route to different specialists based on intermediate results:

def route_after_classify(state) -> str:
    if state["category"] == "billing":
        return "billing_specialist"
    elif state["category"] == "technical":
        return "tech_specialist"
    return "general_agent"

graph.add_conditional_edges("classifier", route_after_classify, {
    "billing_specialist": "billing",
    "tech_specialist": "tech",
    "general_agent": "general",
})

Step 5: Parallel agents

Fan out to multiple agents simultaneously and merge results.

from langgraph.constants import Send

class ParallelState(TypedDict):
    task: str
    subtasks: list[str]
    results: Annotated[list[dict], operator.add]
    final_output: str

def split_task(state: ParallelState) -> list:
    """Fan out subtasks to worker agents."""
    return [Send("worker", {"task": state["task"], "subtask": st}) for st in state["subtasks"]]

def worker(state: dict) -> dict:
    """Each worker handles one subtask."""
    worker_module = dspy.ChainOfThought("task, subtask -> result")
    result = worker_module(task=state["task"], subtask=state["subtask"])
    return {"results": [{"subtask": state["subtask"], "result": result.result}]}

def merge_results(state: ParallelState) -> dict:
    """Combine all worker results into a final output."""
    merger = dspy.ChainOfThought("task, partial_results -> final_output")
    partial = "\n".join(f"- {r['subtask']}: {r['result']}" for r in state["results"])
    result = merger(task=state["task"], partial_results=partial)
    return {"final_output": result.final_output}

graph = StateGraph(ParallelState)
graph.add_node("worker", worker)
graph.add_node("merge", merge_results)
graph.add_conditional_edges(START, split_task)
graph.add_edge("worker", "merge")
graph.add_edge("merge", END)

Step 6: Human-in-the-loop

Pause before agents take critical actions.

from langgraph.checkpoint.memory import MemorySaver

checkpointer = MemorySaver()

# Interrupt before any agent that takes external actions
app = graph.compile(
    checkpointer=checkpointer,
    interrupt_before=["execute_action", "send_email", "update_database"],
)

config = {"configurable": {"thread_id": "task-001"}}

# Run until interrupt
result = app.invoke(input_state, config)
# -> Pauses before "execute_action" node

# Human reviews the proposed action in result state
print(result["proposed_action"])

# If approved, resume from checkpoint
result = app.invoke(None, config)

Step 7: Optimize the team

Per-agent metrics

Optimize each agent's prompts independently first:

def researcher_metric(example, prediction, trace=None):
    """Are the research findings relevant and complete?"""
    judge = dspy.Predict(JudgeResearch)
    return judge(topic=example.topic, findings=prediction.summary).is_good

optimizer = dspy.MIPROv2(metric=researcher_metric, auto="light")
optimized_researcher = optimizer.compile(researcher, trainset=research_trainset)

End-to-end team metric

Then optimize all agents together with a team-level metric:

def team_metric(example, prediction, trace=None):
    """Is the final output high quality?"""
    judge = dspy.Predict(JudgeOutput)
    return judge(
        task=example.task,
        expected=example.output,
        actual=prediction.final_output,
    ).is_good

# Create a module that wraps the full team
class TeamModule(dspy.Module):
    def __init__(self):
        self.supervisor = supervisor_module
        self.researcher = optimized_researcher
        self.writer = writer_module
        self.reviewer = reviewer_module

    def forward(self, task):
        # Run the LangGraph app
        result = app.invoke({"task": task, "messages": [], "current_agent": "", "results": {}, "status": "in_progress"})
        return dspy.Prediction(final_output=result["results"].get("draft", ""))

optimizer = dspy.MIPROv2(metric=team_metric, auto="medium")
optimized_team = optimizer.compile(TeamModule(), trainset=team_trainset)

Key patterns

• One DSPy module per agent — each agent has its own signature, tools, and reasoning strategy
• LangGraph orchestrates, DSPy reasons — LangGraph handles routing and state; DSPy handles what each agent actually thinks
• Supervisor pattern for dynamic routing — when you don't know the order of agents in advance
• Chain pattern for fixed pipelines — when agents always run in the same order (write → edit → review)
• Use Send() for parallel work — fan out to multiple agents simultaneously, merge results after
• Shared state is your communication bus — agents read from and write to the LangGraph state
• Optimize bottom-up — tune individual agents first, then optimize the full team end-to-end
• Interrupt before side effects — use interrupt_before so humans approve actions with real-world consequences

Additional resources

• For worked examples (research team, support escalation), see examples.md
• For the LangChain/LangGraph API reference, see docs/langchain-langgraph-reference.md
• Need a single agent with tools? Start with /ai-taking-actions
• Building a stateless pipeline instead? Use /ai-building-pipelines
• Need the agents to hold conversations? Use /ai-building-chatbots
• Next: /ai-improving-accuracy to measure and improve your agents