Function Calling - Portkey Docs

Functions Usage

The AI Gateway supports the OpenAI signature to define functions. Pass the tools parameter to models that support function/tool calling.

OpenAI NodeJS
OpenAI Python
cURL

import OpenAI from 'openai';

const openai = new OpenAI({
  apiKey: "PORTKEY_API_KEY",
  baseURL: "https://aigw.portkey.ai/v1"
});

async function run() {
  const response = await openai.chat.completions.create({
    model: "MODEL_NAME",
    messages: [{ role: "user", content: "What's the weather like in Boston today?" }],
    tools: [{
        type: "function",
        function: {
          name: "get_current_weather",
          description: "Get the current weather in a given location",
          parameters: {
            type: "object",
            properties: {
              location: {
                type: "string",
                description: "The city and state, e.g. San Francisco, CA",
              },
              unit: { type: "string", enum: ["celsius", "fahrenheit"] },
            },
            required: ["location"],
          },
        }
    }],
    tool_choice: "auto",
  });

  console.log(response.choices[0].message.tool_calls);
}

run();

from openai import OpenAI

openai = OpenAI(
    api_key="PORTKEY_API_KEY",
    base_url="https://aigw.portkey.ai/v1"
)

completion = openai.chat.completions.create(
  model="MODEL_NAME",
  messages=[{"role": "user", "content": "What's the weather like in Boston today?"}],
  tools=[{
    "type": "function",
    "function": {
      "name": "get_current_weather",
      "description": "Get the current weather in a given location",
      "parameters": {
        "type": "object",
        "properties": {
          "location": {
            "type": "string",
            "description": "The city and state, e.g. San Francisco, CA",
          },
          "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]},
        },
        "required": ["location"],
      },
    }
  }],
  tool_choice="auto"
)

print(completion.choices[0].message.tool_calls)

curl "https://aigw.portkey.ai/v1/chat/completions" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $PORTKEY_API_KEY" \
  -d '{
  "model": "MODEL_NAME",
  "messages": [
    {
      "role": "user",
      "content": "What is the weather like in Boston?"
    }
  ],
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "get_current_weather",
        "description": "Get the current weather in a given location",
        "parameters": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "The city and state, e.g. San Francisco, CA"
            },
            "unit": {
              "type": "string",
              "enum": ["celsius", "fahrenheit"]
            }
          },
          "required": ["location"]
        }
      }
    }
  ],
  "tool_choice": "auto"
}'

API Reference

On completion, the request logs in Strata Cloud Manager where tools and functions are visible. The AI Gateway automatically formats the JSON blocks in the input and output for easier debugging.

Managing Functions and Tools in Prompts

Create prompt templates with function/tool definitions in the AI Gateway’s Prompt Library. Set the tool_choice parameter, and the AI Gateway validates your tool definition on the fly, eliminating syntax errors.

Supported Providers and Models

The AI Gateway provides native function calling support across all major AI providers. If you discover a function-calling capable LLM that isn’t working with the AI Gateway, please let us know via Portkey support.

Cookbook

See the detailed cookbook on function calling.

Last modified on September 22, 2026