v139 · AI · Prompt API

Structured Output Studio

Force Gemini Nano to respond as valid JSON by passing a responseConstraint JSON schema. Enter text, pick an analysis type, and receive a guaranteed-valid structured object.

Chrome 148 required: Structured output via responseConstraint needs Chrome 148+ with Gemini Nano enabled. Without it, this demo uses a simulated response to show the concept. See the Prompt Playground for setup instructions.

Input text

Schema

Raw JSON output

// Output appears here

Rendered

JSON Schema used

/* Select a schema above */

API code

const session = await LanguageModel.create({
  systemPrompt: 'You are a text analysis assistant.',
  // Constrain response to valid JSON matching this schema:
  responseConstraint: {
    type: 'json_schema',
    json_schema: {
      name: 'text_analysis',
      schema: {
        type: 'object',
        properties: {
          sentiment: { type: 'string', enum: ['positive', 'neutral', 'negative'] },
          score: { type: 'number', minimum: -1, maximum: 1 },
          keywords: { type: 'array', items: { type: 'string' }, maxItems: 5 },
          summary: { type: 'string', maxLength: 200 },
        },
        required: ['sentiment', 'score', 'keywords', 'summary'],
        additionalProperties: false,
      }
    }
  }
});

const result = await session.prompt(userText);
const data = JSON.parse(result); // guaranteed valid JSON

see also