Does the Router cost money to run?

Yes. The Router uses an LLM API call for every routing decision, which consumes tokens and incurs costs. You can monitor this via the and outputs. If your routing logic can be expressed as simple boolean conditions, use the Condition block instead — it is free and faster.

Router | Sim Docs

The Router block uses AI to intelligently route workflows based on content analysis. Unlike Condition blocks that use simple rules, Routers understand context and intent. Each route you define creates a separate output port, allowing you to connect different paths to different downstream blocks.

Router vs Condition

Use Router when:

AI-powered content analysis is needed
Working with unstructured or varying content
Intent-based routing is required (e.g., "route support tickets to departments")

Use Condition when:

Simple rule-based decisions are sufficient
Working with structured data or numeric comparisons
Fast, deterministic routing is needed

Configuration Options

Context

The context that the Router will analyze to make routing decisions. This is the input data that gets evaluated against your route descriptions. It can be:

A direct user query or input
Output from a previous block
A system-generated message
Any text content that needs intelligent routing

Routes

Define the possible paths that the Router can take. Each route consists of:

Route Title: A name for the route (e.g., "Sales", "Support", "Technical")
Route Description: A clear description of when this route should be selected (e.g., "Route here when the query is about pricing, purchasing, or sales inquiries")

Each route you add creates a separate output port on the Router block. Connect each port to the appropriate downstream block for that route.

Model Selection

Choose an AI model to power the routing decision:

OpenAI: GPT-4o, o1, o3, o4-mini, gpt-4.1
Anthropic: Claude Sonnet 4.5
Google: Gemini 2.5 Pro, Gemini 2.0 Flash
Other Providers: Groq, Cerebras, xAI, DeepSeek
Local Models: Ollama or VLLM compatible models

Use models with strong reasoning capabilities like GPT-4o or Claude Sonnet 4.5 for best results.

API Key

Your API key for the selected LLM provider. This is securely stored and used for authentication.

Outputs

<router.context>: The context that was analyzed
<router.model>: Model used for decision-making
<router.tokens>: Token usage statistics
<router.cost>: Estimated routing cost
<router.selectedRoute>: The ID of the selected route
<router.reasoning>: Explanation of why this route was chosen
<router.selectedPath>: Details of the chosen destination block

Example Use Cases

Customer Support Triage - Route tickets to specialized departments

Input (Ticket) → Router
                  ├── [Sales Route] → Agent (Sales Team)
                  ├── [Technical Route] → Agent (Engineering)
                  └── [Billing Route] → Agent (Finance)

Content Classification - Classify and route user-generated content

Input (Feedback) → Router
                    ├── [Product Feedback] → Workflow (Product Team)
                    └── [Bug Report] → Workflow (Technical Team)

Lead Qualification - Route leads based on qualification criteria

Input (Lead) → Router
                ├── [Enterprise] → Agent (Enterprise Sales)
                └── [Self-serve] → Workflow (Automated Onboarding)

Error Handling

When the Router cannot determine an appropriate route for the given context, it will route to the error path instead of arbitrarily selecting a route. This happens when:

The context doesn't clearly match any of the defined route descriptions
The AI determines that none of the available routes are appropriate

Best Practices

Write clear route descriptions: Each route description should clearly explain when that route should be selected. Be specific about the criteria.
Make routes mutually exclusive: When possible, ensure route descriptions don't overlap to prevent ambiguous routing decisions.
Connect an error path: Handle cases where no route matches by connecting an error handler for graceful fallback behavior.
Use descriptive route titles: Route titles appear in the workflow canvas, so make them meaningful for readability.
Test with diverse inputs: Ensure the Router handles various input types, edge cases, and unexpected content.
Monitor routing performance: Review routing decisions regularly and refine route descriptions based on actual usage patterns.
Choose appropriate models: Use models with strong reasoning capabilities for complex routing decisions.

Common Questions

The Router sends your context and all route descriptions to an LLM, which analyzes the input and selects the route whose description best matches. The LLM is prompted to be deterministic: it always prefers selecting a route over returning no match, and only reports NO_MATCH if the context is completely unrelated to every route description.

When the LLM determines that the context does not match any defined route, it returns NO_MATCH and the Router directs execution to the error path. Connect an error handler to this path for graceful fallback behavior rather than letting the workflow fail silently.

Yes. The Router uses an LLM API call for every routing decision, which consumes tokens and incurs costs. You can monitor this via the <router.tokens> and <router.cost> outputs. If your routing logic can be expressed as simple boolean conditions, use the Condition block instead — it is free and faster.

Yes. The Router V2 block outputs a reasoning field (<router.reasoning>) that contains a brief 1-2 sentence explanation of why the selected route was chosen. This is useful for debugging and understanding routing decisions.

Models with strong reasoning capabilities like GPT-4o or Claude Sonnet 4.5 tend to produce the most accurate routing decisions. For simpler routing scenarios with clearly distinct routes, a faster and cheaper model like GPT-4o-mini or Gemini Flash may be sufficient.

There is no hard limit on the number of routes. Each route you define creates a separate output port on the block. However, keep in mind that more routes with overlapping descriptions make it harder for the LLM to distinguish between them, so aim for clear, mutually exclusive route descriptions.

Router

Common Questions

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