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🚦 Routing

TL;DR: Classify an input and direct it to a specialized handler. Like a train switch — one input takes ONE track.

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Diagram

%%{init: {'theme': 'base', 'themeVariables': {'lineColor': '#64748b'}}}%%
flowchart TB
    classDef user fill:#6366f1,stroke:#4f46e5,stroke-width:2px,color:#ffffff
    classDef main fill:#8b5cf6,stroke:#7c3aed,stroke-width:2px,color:#ffffff
    classDef subagent fill:#ec4899,stroke:#db2777,stroke-width:2px,color:#ffffff
    classDef idle fill:#94a3b8,stroke:#64748b,stroke-width:2px,color:#ffffff

    INPUT["🙋‍♀️📥 User Request"]:::user --> ROUTER{"🐔🚦 Classify & Route"}:::main

    ROUTER -.->|"Type A"| HA["🐦💤 Handler A"]:::idle
    ROUTER -->|"🐔🪺 Type B"| HB["🐦⚡ Handler B"]:::subagent
    ROUTER -.->|"Type C"| HC["🐦💤 Handler C"]:::idle
    ROUTER -.->|"Unknown"| DEFAULT["🐔💤 Default"]:::idle

    HB -->|"🐦📤"| FINAL["💁‍♀️📤 User Receives"]:::user

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Key Insight

┌─────────────────────────────────────────────────────────────────────────────┐
│  🚦 ROUTING: Choose ONE branch                                              │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│  Logic: if/else, switch/case                                                │
│  Question: "Where should I send this?"                                      │
│  Result: Single output from chosen handler                                  │
│                                                                             │
│  Analogy: Train switch → One train takes ONE track                          │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

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Characteristics

Property	Value
Complexity	Low
Parallelism	None
Human-Loop	None
Iteration	None

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When to Use

Routing works well for complex tasks where there are distinct categories that are better handled separately, and where classification can be handled accurately.

Use Case	Routes
Customer support	Bug → Tech Team, Billing → Finance, General → FAQ
Code tasks	Bug fix → Debugger, New feature → Builder
Model routing	Easy → Claude Haiku 4.5, Hard → Claude Sonnet 4.5
Content	Question → Q&A handler, Task → Executor

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When NOT to Use

• All inputs require same processing
• Classification is unreliable
• Categories overlap significantly

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📜 This pattern, as a file

Runnable version (offline mock, no API key · nika check proves the DAG before any token is spent): patterns-as-code/02-routing.nika.yaml — see Patterns as Code.