Overview

Toolcall (Function Calling) is an advanced capability on the StepFun platform. It lets models decide which external tools or functions to invoke to satisfy a user request. By using the Toolcall API, you can extend model capabilities to cover more use cases and offer richer features. Below is a minimal JSON request example that must include three key parameters:


{
	"model": "step-1-8k",
	"messages": [
		{
			"role": "user",
			"content": "Hey, can you calculate (80 + 20) / 5 for me?"
		}
	],
	"tools": [
		{
			"type": "function",
			"function": {
				"name": "Calculator",
				"description": "This StepFun API provides basic arithmetic: addition, subtraction, multiplication, and division.",
				"parameters": {
					"properties": {
						"formula": {
							"type": "string",
							"description": "Expression to evaluate. Only integers are supported. Operators: +, -, *, /, and parentheses. Example: (1 + 2) * 3."
						}
					},
					"type": "object"
				}
			}
		}
	]
}

model: model name

The following models support Toolcall requests:

step-1-8k
step-1-32k
step-1v-8k
step-1v-32k
step-1-128k
step-1-256k

Official tools

StepFun provides these built-in tools; configure them to enable the capability directly:

Web search: call a search engine to fetch the latest information.
Knowledge base search: upload text to a knowledge base and search it to reduce hallucinations.

tools: list of functions

Use tools to describe the functions available locally. Up to 128 tools are allowed. Each entry has type function and contains a function object with the name, description, and parameters.

name: letters, numbers, -, _; ideally under 64 characters. Use a clear English name so the model understands it (regex guideline: ^[a-zA-Z*][a-zA-Z0-9-_]63$).
parameters: root type must be object. The content follows a subset of JSON Schema; keys follow the same naming rule. See JSON Schema for supported type values. description explains each parameter.
description: explains what the function does so the model can choose it; English or Chinese is supported.

messages: conversation context

See Chat Completion request object.

Examples


from openai import OpenAI
 
client = OpenAI(api_key = "STEP_API_KEY", base_url = "https://api.stepfun.ai/v1")
 
completion = client.chat.completions.create(
model = "step-1-8k",
messages = [
{
"role": "user",
"content": "Can you calculate (80 + 20) / 5 for me?"
}],
tools = [
{
"type": "function",
"function":
{
"name": "Calculator",
"description": "This StepFun API provides basic arithmetic: addition, subtraction, multiplication, and division.",
"parameters":
{
"type": "object",
"properties":
{
"formula":
{
"type": "string",
"description": "Expression to evaluate. Only integers are supported. Operators: +, -, *, /, and parentheses. Example: '(1 + 2) * 3'."
}
}
}
}
}]
)
 
print(completion)


import OpenAI from "openai";
 
const openai = new OpenAI(
{
apiKey: "STEP_API_KEY",
baseURL: "https://api.stepfun.ai/v1"
});
 
async function main() {
const completion = await openai.chat.completions.create(
{
model: "step-1-8k",
messages: [
{
"role": "user",
"content": "Can you calculate (80 + 20) / 5 for me?"
}],
tools: [
{
"type": "function",
"function":
{
"name": "Calculator",
"description": "This StepFun API provides basic arithmetic: addition, subtraction, multiplication, and division.",
"parameters":
{
"type": "object",
"properties":
{
"formula":
{
"type": "string",
"description": "Expression to evaluate. Only integers are supported. Operators: +, -, *, /, and parentheses. Example: '(1 + 2) * 3'."
}
}
}
}
}]
});
 
console.log(JSON.stringify(completion));
 
}
 
main();


curl https://api.stepfun.ai/v1/chat/completions \
-H "Content-Type: application/json" \
-H "Authorization: Bearer $STEP_API_KEY" \
-d '{
"model": "step-1-8k",
"messages": [
    {
        "role": "user",
        "content": "Can you calculate (80 + 20) / 5 for me?"
    }
],
"tools": [
    {
        "type": "function",
        "function":  {
            "name": "Calculator",
            "description": "This StepFun API provides basic arithmetic: addition, subtraction, multiplication, and division.",
            "parameters": {
                "type": "object",
                "properties": {
                    "formula": {
                        "type": "string",
                        "description": "Expression to evaluate. Only integers are supported. Operators: +, -, *, /, and parentheses. Example: (1 + 2) * 3."
                    }
                }
            }
        }
    }
]
}'

Response


{
    "id": "b7b56af0-52a6-483f-a589-948182676a1b",
    "object": "chat.completion",
    "created": 1717744611,
    "model": "step-1-8k",
    "choices":
    [
        {
            "index": 0,
            "message":
            {
                "role": "assistant",
                "content": "",
                "tool_calls":
                [
                    {
                        "id": "call_ybVBO_JASgipgJH8xWbhKg",
                        "type": "function",
                        "function":
                        {
                            "name": "Calculator",
                            "arguments": "{\"formula\": \"(80 + 20) / 5\"}"
                        }
                    }
                ]
            },
            "finish_reason": "stop"
        }
    ],
    "usage":
    {
        "prompt_tokens": 151,
        "completion_tokens": 25,
        "total_tokens": 176
    }
}