Router

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When to use it

• Incoming requests could be answered by multiple skills—agents with tools, direct MCP servers, or lightweight functions.
• You want dynamic dispatch instead of a maze of if/else statements or handcrafted prompts.
• You need confidence scores and rationale so a human (or another workflow) can make the final decision.
• You want to fall back to a generalist agent when no high-confidence match is found.

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Destinations and scoring

• category: "agent", "server", or "function".
• result: the routed object (an Agent/AugmentedLLM, a server name, or a callable).
• confidence: "high", "medium", or "low"—computed from the model’s probability.
• reasoning: the model’s natural language justification.

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Quick start

from mcp_agent.app import MCPApp
from mcp_agent.mcp.gen_client import gen_client
from mcp_agent.workflows.factory import AgentSpec, create_router_llm

app = MCPApp(name="router_example")

async def main():
    async with app.run() as running_app:
        router = await create_router_llm(
            name="support_router",
            server_names=["filesystem", "fetch"],
            agents=[
                AgentSpec(
                    name="finder",
                    instruction="Locate relevant files or URLs using MCP tools.",
                    server_names=["filesystem", "fetch"],
                ),
                AgentSpec(
                    name="writer",
                    instruction="Draft polished responses using prior context.",
                ),
            ],
            functions=[
                lambda _: "Fallback: escalate to human triage.",
            ],
            routing_instruction="Prefer agents when tool use is required; use functions only for trivial replies.",
            provider="openai",
            context=running_app.context,
        )

        decisions = await router.route("Print the contents of README.md", top_k=2)
        for choice in decisions:
            print(choice.category, choice.result, choice.confidence, choice.reasoning)

        top = decisions[0]
        if top.category == "agent":
            async with top.result:  # Attach LLMs + MCP tools for the agent
                return await top.result.generate_str("Show me README.md")
        if top.category == "server":
            async with gen_client(
                top.result,
                running_app.server_registry,
                context=running_app.context,
            ) as session:
                file = await session.call_tool("read_file", {"path": "README.md"})
                return file.content
        if top.category == "function":
            return top.result("README.md")

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Configuration knobs

• top_k: expose the top k candidates to give humans (or downstream logic) choices.
• routing_instruction: prime the classifier with custom rubric; defaults to a generic prompt that lists every destination, its description, and available tools.
• provider / model: choose the model that performs routing (openai or anthropic today). You can also pass request_params for temperature, stop sequences, or strict JSON mode.
• server_names: include raw MCP servers. The router pulls descriptions from the server registry so the model knows what each server can do.
• functions: register local Python callables. Handy for telemetry, logging, or immediate fallbacks.
• route_to_agent / route_to_server / route_to_function: skip the multi-category prompt when you already know the desired destination type.
• create_router_embedding: swap in embedding similarity when you prefer deterministic scoring or offline model execution.

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Guardrails and observability

• Use the confidence signal to decide when to short-circuit or escalate. For example, enforce confidence == "high" before allowing automated actions.
• The router records detailed spans (router.route, candidate reasoning, chosen categories) when tracing is enabled, making it easy to debug ambiguous decisions in Jaeger or another OTLP backend.
• Pair with the Intent Classifier for two-stage routing: first map the request to an intent, then feed the intent into the router for fine-grained dispatch.
• Wrap the router itself in the Evaluator-Optimizer pattern if you want an automated supervisor to veto low-quality routing rationales.

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Example projects

• workflow_router – routes across agents, MCP servers, and plain functions with confidence/rationale logging.
• workflow_intent_classifier – classifies intent first, then routes to specialised handlers.
• Temporal router – demonstrates durable routing inside Temporal workflows.

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Related reading

• Intent Classifier pattern
• Workflow & decorators guide