How to Beginner to Intermediate · 3 min read

How to make AI follow a specific format

Quick answer

To make AI follow a specific format, explicitly define the desired structure in your prompt using clear instructions and examples. Use delimiters, bullet points, or JSON templates within the prompt to guide models like gpt-4o to produce output in the exact format you need.

PREREQUISITES

Python 3.8+
OpenAI API key (free tier works)
pip install openai>=1.0

Setup

Install the OpenAI Python SDK and set your API key as an environment variable to authenticate requests.

bash

pip install openai>=1.0

Step by step

Use explicit instructions and a clear example format in your prompt. This example shows how to instruct gpt-4o to output a JSON object with specific fields.

python

import os
from openai import OpenAI

client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])

prompt = '''
You are a helpful assistant. Please respond ONLY in the following JSON format without extra text:
{
  "name": "string",
  "age": integer,
  "email": "string"
}

Example:
{
  "name": "Alice",
  "age": 30,
  "email": "alice@example.com"
}

Now provide the JSON for a person named Bob, age 25, email bob@example.com.
'''

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": prompt}]
)

print(response.choices[0].message.content)

output

{
  "name": "Bob",
  "age": 25,
  "email": "bob@example.com"
}

Common variations

You can adapt the format instructions for other output types like XML, CSV, or markdown tables. Also, use different models or async calls as needed.

python

import os
from openai import OpenAI

client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])

async def get_formatted_response():
    prompt = '''
Respond ONLY in CSV format with columns: name,age,email
Example:
name,age,email
Alice,30,alice@example.com

Now provide data for Bob, 25, bob@example.com.
'''

    response = await client.chat.completions.acreate(
        model="gpt-4o",
        messages=[{"role": "user", "content": prompt}]
    )
    print(response.choices[0].message.content)

# To run async function:
# import asyncio
# asyncio.run(get_formatted_response())

output

name,age,email
Bob,25,bob@example.com

Troubleshooting

If the AI output includes extra text or deviates from the format, reinforce instructions by adding phrases like "Respond ONLY with the format" or provide multiple examples. Also, consider using temperature=0 for deterministic output.

python

import os
from openai import OpenAI

client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])

prompt = '''
Respond ONLY with this JSON format, no extra text:
{
  "title": "string",
  "year": integer
}

Example:
{
  "title": "Inception",
  "year": 2010
}

Now provide the JSON for "The Matrix", 1999.
'''

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": prompt}],
    temperature=0
)

print(response.choices[0].message.content)

output

{
  "title": "The Matrix",
  "year": 1999
}

✅

Key Takeaways

Always specify the exact output format with clear instructions and examples in your prompt.
Use delimiters or structured templates like JSON or CSV to guide AI output.
Set temperature=0 to reduce randomness and improve format adherence.
Reinforce instructions by telling the AI to respond ONLY in the desired format.
Test with multiple examples to ensure consistent formatting.

Verified 2026-04 · gpt-4o

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