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The purpose of a Network’s Router is to decide what Agent to call based off the current Network State.

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What is a Router?

A router is a function that gets called after each agent runs, which decides whether to:
  1. Call another agent (by returning an Agent)
  2. Stop the network’s execution loop (by returning undefined)
The routing function gets access to everything it needs to make this decision:
  • The Network object itself, including it’s State.
  • The stack of Agents to be called.
  • The number of times the Network has called Agents (the number of iterations).
  • The result from the previously called Agent in the Network’s execution loop.
For more information about the role of a Router in a Network, read about how Networks work.

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Using a Router

Providing a custom Router to your Network is optional. If you don’t provide one, the Network will use the “Default Router” Routing Agent.
Providing a custom Router to your Network can be achieved using 3 different patterns:
  • Writing a custom Code-based Router: Define a function that makes decisions based on the current State.
  • Creating a Routing Agent: Leverages LLM calls to decide which Agents should be called next based on the current State.
  • Writing a custom Hybrid Router: Mix code and agent-based routing to get the best of both worlds.

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Creating a custom Router

Custom Routers can be provided by defining a defaultRouter function returning either an instance of an Agent object or undefined. 
import { createNetwork } from "@inngest/agent-kit";

// classifier and writer Agents definition...

const network = createNetwork({
  agents: [classifier, writer],
  router: ({ lastResult, callCount }) => {
    // retrieve the last message from the output
    const lastMessage = lastResult?.output[lastResult?.output.length - 1];
    const content =
      lastMessage?.type === "text" ? (lastMessage?.content as string) : "";
    // First call: use the classifier
    if (callCount === 0) {
      return classifier;
    }
    // Second call: if it's a question, use the writer
    if (callCount === 1 && content.includes("question")) {
      return writer;
    }
    // Otherwise, we're done!
    return undefined;
  },
});
The defaultRouter function receives a number of arguments:
@inngest/agent-kit
interface RouterArgs {
  network: Network; // The entire network, including the state and history
  stack: Agent[]; // Future agents to be called
  callCount: number; // Number of times the Network has called agents
  lastResult?: InferenceResult; // The the previously called Agent's result
}
The available arguments can be used to build the routing patterns described below.

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Routing Patterns

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Tips

  • Start simple with code-based routing for predictable behavior, then add agent-based routing for flexibility.
  • Remember that routers can access the network’s state
  • You can return agents that weren’t in the original network
  • The router runs after each agent call
  • Returning undefined stops the network’s execution loop
That’s it! Routing is what makes networks powerful - it lets you build workflows that can be as simple or complex as you need.

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Code-based Routers (supervised routing)

The simplest way to route is to write code that makes decisions. Here’s an example that routes between a classifier and a writer: 
import { createNetwork } from "@inngest/agent-kit";

// classifier and writer Agents definition...

const network = createNetwork({
  agents: [classifier, writer],
  router: ({ lastResult, callCount }) => {
    // retrieve the last message from the output
    const lastMessage = lastResult?.output[lastResult?.output.length - 1];
    const content =
      lastMessage?.type === "text" ? (lastMessage?.content as string) : "";
    // First call: use the classifier
    if (callCount === 0) {
      return classifier;
    }
    // Second call: if it's a question, use the writer
    if (callCount === 1 && content.includes("question")) {
      return writer;
    }
    // Otherwise, we're done!
    return undefined;
  },
});
Code-based routing is great when you want deterministic, predictable behavior. It’s also the fastest option since there’s no LLM calls involved.

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Routing Agent (autonomous routing)

Without a defaultRouter defined, the network will use the “Default Routing Agent” to decide which agent to call next. The “Default Routing Agent” is a Routing Agent provided by Agent Kit to handle the default routing logic. You can create your own Routing Agent by using the createRoutingAgent helper function: 
import { createRoutingAgent } from "@inngest/agent-kit";

const routingAgent = createRoutingAgent({
  name: "Custom routing agent",
  description: "Selects agents based on the current state and request",
  lifecycle: {
    onRoute: ({ result, network }) => {
      // custom logic...
    },
  },
});

// classifier and writer Agents definition...

const network = createNetwork({
  agents: [classifier, writer],
  router: routingAgent,
});
Routing Agents look similar to Agents but are designed to make routing decisions: - Routing Agents cannot have Tools. - Routing Agents provides a single onRoute lifecycle method.

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Hybrid code and agent Routers (semi-supervised routing)

And, of course, you can mix code and agent-based routing. Here’s an example that uses code for the first step, then lets an agent take over: 
import { createNetwork, getDefaultRoutingAgent } from "@inngest/agent-kit";

// classifier and writer Agents definition...

const network = createNetwork({
  agents: [classifier, writer],
  router: ({ callCount }) => {
    // Always start with the classifier
    if (callCount === 0) {
      return classifier;
    }
    // Then let the routing agent take over
    return getDefaultRoutingAgent();
  },
});
This gives you the best of both worlds:
  • Predictable first steps when you know what needs to happen
  • Flexibility when the path forward isn’t clear

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Using state in Routing

The router is the brain of your network - it decides which agent to call next. You can use state to make smart routing decisions: 
import { createNetwork } from '@inngest/agent-kit';

// mathAgent and contextAgent Agents definition...

const network = createNetwork({
  agents: [mathAgent, contextAgent],
  router: ({ network, lastResult }): Agent | undefined => {
    // Check if we've solved the problem
    const solution = network.state.data.solution;
    if (solution) {
      // We're done - return undefined to stop the network
      return undefined;
    }

    // retrieve the last message from the output
    const lastMessage = lastResult?.output[lastResult?.output.length - 1];
    const content = lastMessage?.type === 'text' ? lastMessage?.content as string : '';

    // Check the last result to decide what to do next
    if (content.includes('need more context')) {
      return contextAgent;
    }

    return mathAgent;
  };
});

Networks

Networks combines the State and Router to execute Agent workflows.

State

State is a key-value store that can be used to store data between Agents.