Structured Output in Large Language Models (LLMs)

Mehmet Ozkaya
5 min readNov 19, 2024

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we’re diving into an exciting aspect of Large Language Models (LLMs): Structured Output. While LLMs like GPT-4 are renowned for generating free-form text, they can also produce structured outputs, which is incredibly useful when we need results in a specific, machine-readable format like JSON or XML.

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In this article, we’ll explore:

  • What structured output is.
  • Why it’s important.
  • How to guide LLMs to generate structured outputs.
  • Hands-on examples to see it in action.
  • The benefits of using structured outputs.

What is Structured Output?

Structured output refers to data presented in a well-defined format, such as JSON, XML, tables, or key-value pairs. Unlike free-flowing text, structured output is organized in a way that machines can easily parse and understand.

  1. Machine-Readable: Structured outputs are designed to be easily processed by computers, making data exchange between systems seamless.
  2. Consistency: They follow predefined schemas or formats, ensuring that the data structure remains consistent across different outputs.

Examples: Common structured formats include:

  • JSON: { "name": "Alice", "age": 30 }
  • XML: <person><name>Alice</name><age>30</age></person>
  • CSV/Tables: name, age\nAlice, 30

Think of it as the difference between writing a paragraph and filling out a form. Structured output is like the form — data is organized in predefined fields.

Why Do We Need Structured Output?

LLMs are inherently stochastic, meaning their outputs can vary even with the same input. This variability can be a challenge when you need predictable, reliable outputs for applications like APIs or automation workflows.

Predictability and Consistency:

  • Challenge: Free-form text can be unpredictable, making it hard to parse and extract specific information.
  • Solution: Structured output ensures that the data follows a clear and consistent format every time.

Machine Integration:

  • APIs and Automation: Systems often require data in specific formats to process it automatically.
  • Data Parsing: Structured data can be easily parsed and integrated into databases, applications, or further processing pipelines.

Efficiency:

  • Reduces Post-Processing: There’s no need to clean or reformat the data after receiving it.
  • Error Reduction: Consistent formats minimize the risk of errors during data handling.

Examples of When Structured Outputs Are Useful

Structured outputs shine in various scenarios:

1. API Calls and Function Responses

When an LLM interacts with external systems via APIs, the responses often need to be in a format like JSON for easy parsing.

Example:

  • Prompt: “Provide the weather information for New York City in JSON format.”
  • Response:
  • { "city": "New York City", "temperature": "72°F", "conditions": "Partly Cloudy" }

2. Automating Workflows

In tasks like scheduling, data retrieval, or task automation, structured outputs allow the LLM to return data consistently, facilitating seamless automation.

Example:

  • Prompt: “Schedule a meeting for next Monday at 2 PM and provide the details in JSON.”
  • Respons
  • { "event": "Meeting", "date": "YYYY-MM-DD", "time": "14:00", "status": "Scheduled" }

3. Data Extraction and Storage

When extracting information from documents or generating reports, structured formats make it easier to store and retrieve data from databases.

Example:

  • Prompt: “Extract the key points from this article and present them in a JSON array.”
  • Response:
  • { "key_points": [ "Point 1", "Point 2", "Point 3" ] }

How Does Structured Output Work?

To get an LLM to produce structured output, you need to guide it with specific instructions in your prompt.

Specify the Desired Format:

  • Clearly state the format you want the output in.
  • Provide an example or template if possible.

Provide Clear Instructions:

  • Use precise language to minimize ambiguity.
  • Indicate any specific fields or keys you need.

Prompt:

Please provide the weather information for New York City in the following JSON format:
{
"city": "city name",
"temperature": "value",
"conditions": "description"
}

Expected Response:

{
"city": "New York City",
"temperature": "72°F",
"conditions": "Partly Cloudy"
}

By specifying the exact format, you guide the model to produce output that is predictable and machine-readable.

Hands-on Example — JSON Output for Weather Data

Let’s put this into practice using the OpenAI Playground.

Note: The OpenAI Playground is a web-based tool that allows you to interact with LLMs like GPT-4. You can input prompts and adjust settings to see how the model responds.

Access the Playground:

Set the Response Format:

  • Ensure the model knows you want a JSON response.

Enter the Prompt:

  • Please provide the weather information for New York City in the following JSON format: { "city": "city name", "temperature": "value", "conditions": "description" }

Submit the Prompt:

  • Click “Submit” to generate the response.

Review the Output:

  • The model should produce:
  • { "city": "New York City", "temperature": "72°F", "conditions": "Partly Cloudy" }

Tips:

  • Be Explicit: The clearer your instructions, the more likely the model will follow them accurately.
  • Test Different Prompts: Experiment with various ways of instructing the model to see what yields the best results.

Benefits of Structured Output

Structured output offers several advantages:

1. Consistent and Predictable Format

  • Reliability: Ensures that every output follows the same structure.
  • Ease of Use: Makes it straightforward to write programs that consume the data.

2. Easy Integration with Systems

  • APIs and Databases: Structured data can be directly fed into APIs or stored in databases without additional formatting.
  • Automation: Facilitates automated workflows where consistent data formats are crucial.

3. Reduces Post-Processing

  • Efficiency: Saves time by eliminating the need to parse or clean the data after receiving it.
  • Error Reduction: Minimizes the chances of errors during data handling due to inconsistent formats.

Conclusion

Structured output is a powerful feature that enhances the versatility of Large Language Models. By guiding the model to produce data in specific formats, you can:

  • Integrate LLMs with other systems: Seamlessly connect AI-generated data with your applications, databases, or APIs.
  • Automate Tasks: Streamline workflows that require consistent data inputs.
  • Improve Predictability: Ensure that the model’s outputs are consistent and reliable.

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Mehmet Ozkaya
Mehmet Ozkaya

Written by Mehmet Ozkaya

Software Architect | Udemy Instructor | AWS Community Builder | Cloud-Native and Serverless Event-driven Microservices https://github.com/mehmetozkaya

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