Domain Signal

Overview

domain classifies the request topic family. Define domain rules under routing.signals.domains.

The detector uses the classifier configured under global.model_catalog.modules.classifier and its model bindings under global.model_catalog.system.

Key Advantages

• Routes by topic without hard-coding every phrase into keyword lists.
• Keeps domain policy reusable across multiple decisions.
• Supports stable category families that are easy to audit.
• Works well as the first learned signal in a routing graph.

What Problem Does It Solve?

Keyword routing breaks down once prompts are paraphrased or when domain boundaries are broader than a handful of phrases.

domain solves that by mapping topic classification into named routing signals that decisions can compose with complexity, safety, or plugin logic.

When to Use

Use domain when:

• routes are organized around topic families
• lexical matching is too brittle
• the same topic boundary should feed several decisions
• you want a stable learned classifier before adding more specialized signals

Configuration

routing:
  signals:
    domains:
      - name: business
        description: Business and management related queries.
        mmlu_categories: [business]
      - name: law
        description: Legal questions and law-related topics.
        mmlu_categories: [law]
      - name: psychology
        description: Psychology and mental health topics.
        mmlu_categories: [psychology]
      - name: health
        description: Health and medical information queries.
        mmlu_categories: [health]
      - name: other
        description: General fallback traffic.
        mmlu_categories: [other]

Keep domain names stable because decisions reference those names directly.

Local and remote classifier selection

With no backend, category/domain classification keeps its existing local model behavior. Use variant: candle, variant: modernbert, or variant: mmbert32k for an explicit local selector; the deprecated use_modernbert and use_mmbert_32k keys remain readable for compatibility but are normalized to variant in canonical output. An agreeing canonical and legacy selector is accepted; contradictory active selectors are rejected.

A remote category classifier uses the shared backend block. Its model is an explicit name from global.model_catalog.external[], and that catalog entry must have model_role: classification. Category currently accepts only the http_classify protocol and the label_distribution.v1 contract so the full label distribution continues to feed domain matching and routing decisions.

global:
  model_catalog:
    external:
      - name: domain-service
        model_role: classification
        llm_endpoint:
          address: domain-classifier.default.svc
          port: 8080
        llm_model_name: domain-intent-v1
    modules:
      classifier:
        domain:
          backend:
            protocol: http_classify
            contract: label_distribution.v1
            model: domain-service
            deadline_ms: 5000

Dependencies and Limitations

Domain classification uses the configured classifier module and processes the request text. Treat other as a fallback, and re-evaluate labels and thresholds when the classifier changes. See a complete example: config/fragments/signal/domain/mmlu.yaml.