Thursday 25 January 2024

Get structured JSON data back from GPT-4-Turbo

With the latest gpt-4-turbo model out recently, there is one very helpful feature which came with it: The JSON mode option. Using JSON mode, we are able to predictably get responses back from OpenAI in structured JSON format. 

This can help immensely when building APIs using Large Language Models (LLMs). Even though the model can be instructed to return JSON in it's system prompt, previously, there was no guarantee that the model would return valid JSON. With the JSON mode option now, we can specify the required format and the model will return data according to it. 

To know more about JSON mode, have a look at the official OpenAI docs:

Now let's look at some code to see how this works in action:

I am using the Azure OpenAI service to host the gpt-4-turbo model and I am also using the v1.0.0.-beta.12 version of the Azure OpenAI .NET SDK found on NuGet here:

What is happening in the code is that in the system message, we are instructing the LLM that analyse the text provided by the user and then extract the cities mentioned in this text and return them in the specified JSON format. 

Also important is line 22 where we explicitly specify to use the response format as JSON.   

Next, we provide the actually text to parse in the user message. 

Once we get the data back in expected JSON schema, we are able to convert it to objects which can be used in code.

And as expected we get the following output:

Hope this helps!