Module 8: Structured Output and Schema Design

Lesson 4: Enums and Constraints

The ultimate defense against hallucination is the Constraint. If you give Claude a blank text box, it will fill it with poetry. If you give Claude a drop-down menu, it will pick an option.

In this lesson, we master the enum and constraint keywords that turn "Probabilistic Words" into "Deterministic Tokens."

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1. The Power of Enums

An enum provides a fixed list of valid strings.

"sentiment": {
  "type": "string",
  "enum": ["Positive", "Negative", "Neutral"]
}

Why Enums are "Magic":

When Claude generates tokens for an enum property, the model's internal probability for those specific words (Positive, Negative, Neutral) spikes to nearly 100%. Claude cannot output "Happy" or "Sad" if the enum is strictly defined.

Architect's Move: Use Enums for any categorical data (e.g., Status codes, Departments, priority levels).

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2. Numeric Constraints: minimum and maximum

Don't just trust Claude to provide a "Realistic" number. Force it.

• Example: "rating": { "type": "integer", "minimum": 1, "maximum": 5 }

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3. String Constraints: minLength and maxLength

If you need a "Brief Summary," don't just say "Briefly."

• Action: "summary": { "type": "string", "maxLength": 100 }

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4. Pattern Recognition (RegEx)

The pattern keyword allows you to use Regular Expressions to validate strings. This is perfect for dates, IDs, or phone numbers.

"phone": {
  "type": "string",
  "pattern": "^\\d{3}-\\d{3}-\\d{4}$"
}

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5. Visualizing the Constraint Engine

graph TD
    A[Model Intelligence] --> B{Schema Filter}
    B -->|Enum| C[Fixed Choice]
    B -->|Range| D[Bounded Number]
    B -->|Pattern| E[RegEx Format]
    C --> F[100% Reliable Output]
    D --> F
    E --> F

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6. Summary

• Enums are your strongest weapon against hallucination.
• Ranges prevent mathematical absurdities.
• Patterns (RegEx) enforce technical formats.

In the final lesson of this module, we look at how to verify these outputs: Validation Strategies.

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Interactive Quiz

1. Explain why an enum reduces model hallucination.
2. What is the difference between minimum and exclusiveMinimum?
3. How can you use the pattern keyword to suggest a specific date format?
4. Setup an Enum for "Traffic_Light_State" with 3 valid options.

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Reference Video: