Structured Output Enforcer

Structured Output Enforcer

Prerequisites & Dependencies

• Node.js 18+ with npm or pnpm
• Mandatory packages: npm i zod for runtime validation and type inference, or npm i jsonschema for pure JSON Schema validation
• Optional: npm i ai-sdk or npm i openai to integrate with LLM APIs
• TypeScript for type-safe Zod schemas (highly recommended)

Execution Steps

1. Define a Zod schema (or JSON Schema) that describes the expected output structure: required fields, types, enums, arrays, and nested objects
2. Call the LLM with a prompt that instructs it to output JSON matching the schema (e.g., Output valid JSON only, matching this schema:...)
3. Parse the LLM's raw response as JSON (strip markdown fences if needed)
4. Validate the parsed object against the Zod schema using z.parse(data) or schema.safeParse(data)
5. If validation fails, retry with a refined prompt that includes the error details and schema excerpt
6. On success, return the validated JSON object to the caller; log and discard invalid attempts after N retries
7. Optionally generate TypeScript types from the Zod schema: z.infer<typeof schema> for end-to-end type safety

// Example: Zod schema for LLM-structured output
import { z } from 'zod';

const UserProfileSchema = z.object({
  name: z.string().min(1, 'Name is required'),
  age: z.number().int().min(13).max(120, 'Age must be between 13 and 120'),
  email: z.string().email('Invalid email address'),
  role: z.enum(['admin', 'user', 'guest'], 'Role must be admin, user, or guest'),
  preferences: z.object({
    theme: z.enum(['light', 'dark', 'system']),
    notifications: z.boolean(),
  }),
});

type UserProfile = z.infer<typeof UserProfileSchema>;

// Simulated LLM output (would come from OpenAI/Anthropic API call)
const rawLLMOutput = `{
  "name": "Alice",
  "age": 30,
  "email": "alice@example.com",
  "role": "user",
  "preferences": {
    "theme": "dark",
    "notifications": true
  }
}`;

try {
  const parsed = UserProfileSchema.parse(JSON.parse(rawLLMOutput));
  console.log('Validated user profile:', parsed);
} catch (error) {
  console.error('Validation errors:', error.errors);
}

npm i zod
npm i -D @types/zod