JSON & AI/LLM — Structured Output, Function Calling & Tool Use

1const response = await openai.chat.completions.create({
2  model: 'gpt-4o',
3  response_format: { type: 'json_object' },
4  messages: [
5    {
6      role: 'system',
7      content: 'Extract product details as JSON with keys: name, price, category, inStock',
8    },
9    {
10      role: 'user',
11      content: 'The Blue Widget costs $29.99 and is currently available in the Electronics section.',
12    },
13  ],
14});
15
16const product = JSON.parse(response.choices[0].message.content!);
17// { "name": "Blue Widget", "price": 29.99, "category": "Electronics", "inStock": true }

1const response = await openai.chat.completions.create({
2  model: 'gpt-4o',
3  response_format: {
4    type: 'json_schema',
5    json_schema: {
6      name: 'product_extraction',
7      strict: true,
8      schema: {
9        type: 'object',
10        properties: {
11          name: { type: 'string' },
12          price: { type: 'number' },
13          category: { type: 'string', enum: ['Electronics', 'Clothing', 'Home', 'Other'] },
14          inStock: { type: 'boolean' },
15        },
16        required: ['name', 'price', 'category', 'inStock'],
17        additionalProperties: false,
18      },
19    },
20  },
21  messages: [
22    { role: 'user', content: 'The Blue Widget costs $29.99, available in Electronics.' },
23  ],
24});
25
26// Output is GUARANTEED to match the schema
27const product = JSON.parse(response.choices[0].message.content!);

1You are a data extraction assistant. Extract information from user text
2and return it as a JSON object matching this exact structure:
3
4{
5  "name": "string (product name)",
6  "price": number (in dollars, e.g. 29.99),
7  "features": ["string array of key features"],
8  "rating": number (1-5, or null if not mentioned),
9  "available": boolean
10}
11
12Rules:
13- Return ONLY the JSON object, no markdown fences, no explanation
14- Use null for fields not found in the text
15- Price must be a number, not a string
16- Features array can be empty if none mentioned

1const messages = [
2  { role: 'system', content: 'Extract event details as JSON.' },
3  // Example 1
4  { role: 'user', content: 'React Conf on May 15 at 2pm in Las Vegas' },
5  { role: 'assistant', content: JSON.stringify({
6    event: 'React Conf', date: '2026-05-15', time: '14:00', location: 'Las Vegas',
7  })},
8  // Example 2
9  { role: 'user', content: 'Team standup tomorrow morning' },
10  { role: 'assistant', content: JSON.stringify({
11    event: 'Team standup', date: 'tomorrow', time: 'morning', location: null,
12  })},
13  // Actual request
14  { role: 'user', content: userInput },
15];