How can I enforce structured function call responses in my Choose-Your-Own-Adventure assistant?

Below is one approach that many developers have found effective:

Use Structured, Strict Responses

When setting up your assistant, you can enforce a strict output format for function calls. By using the Assistants API’s "structured outputs" feature with the strict parameter (e.g., strict: true), you can require that any function call be returned as a proper function call object rather than being output as plain markdown code. This tells the model:

• When to call a function: If the story enters a new location, the assistant should output a function call (as a JSON object with the function name and parameters) rather than embedding it in text or as a markdown code block.
• How to output the call: The function call should be returned in a structured manner (for instance, using the function_call field) rather than as part of the narrative text.

Adjust your Prompt

Include clear instructions in your prompt (for example, in the system or developer instructions) that state:

• For new locations: “Whenever the story enters a new location, call the provided function using the structured function calling mechanism. Output only the function call object (do not wrap it in markdown or code blocks) and do not include additional text.”
• Format expectations: “The output must be a JSON object with keys like name and arguments for the function call. Any deviation from this format is considered incorrect.”

Example

In your system prompt you might add:

MARKDOWNCopied
You are a Choose-Your-Own-Adventure Assistant. When the story reaches a new location, do not output the function call as plain text or inside a markdown code block. Instead, output a structured function call object in JSON format with the following keys:
- name: the function name (e.g., call_new_location_function)
- arguments: an object with the location parameter

Do not include any extra text. If no new location is reached, simply continue the narrative.

Benefits

This explicit instruction helps the model:

• Recognize when it must return a function call instead of text.
• Adhere to the API expectations of using a structured function call, thus triggering the proper “requires_action” state.

In summary, reinforce the desired output format by combining:

1. The strict structured output settings in your function calling parameters.
2. Explicit instructions in your prompt that define when, how, and what format the function call should take.

This combination is the key to guiding the model to correctly understand and use the function calling mechanism instead of embedding function calls in markdown or plain text.