--- title: Tool Calls product: vercel url: /docs/ai-gateway/sdks-and-apis/openai-chat-completions/tool-calling canonical_url: "https://vercel.com/docs/ai-gateway/sdks-and-apis/openai-chat-completions/tool-calling" last_updated: 2026-07-28 type: conceptual prerequisites: - /docs/ai-gateway/sdks-and-apis/openai-chat-completions - /docs/ai-gateway/sdks-and-apis related: [] summary: Use function calling with the Chat Completions API to enable models to call tools and functions through AI Gateway. install_vercel_plugin: npx plugins add vercel/vercel-plugin --- # Tool Calls The Chat Completions API supports function calling, allowing models to call tools and functions. This follows the same specification as the [OpenAI Function Calling API](https://platform.openai.com/docs/guides/function-calling). ## Related pages > **For AI agents:** Follow these links to understand how this page connects to the rest of the Vercel ecosystem. For the full cross-link map (inbound, outbound, prerequisites, and semantic neighbors), see the .graph.md link below. - [Tool Calling](https://vercel.com/docs/ai-gateway/sdks-and-apis/anthropic-messages-api/tool-calling?from=related) — Use function calling with the Anthropic Messages API to allow models to call tools and functions. - [Tool Calling](https://vercel.com/docs/ai-gateway/sdks-and-apis/openresponses/tool-calling?from=related) — Define tools the model can call using the OpenResponses API. - [Tools](https://ai-sdk.dev/docs/foundations/tools?from=related) - [What is an LLM Tool?](https://vercel.com/kb/guide/what-is-an-llm-tool?from=related) — Learn what tools are, how tool calling works, and how you can use them to build agents. - [Tool Calling](https://vercel.com/docs/ai-gateway/sdks-and-apis/responses/tool-calling?from=related) — Define tools the model can call with the OpenAI Responses API. - [Call Tools](https://ai-sdk.dev/cookbook/next/call-tools?from=related) - [Call Tools](https://ai-sdk.dev/cookbook/node/call-tools?from=related) - [@v0-sdk/ai-tools](https://v0.app/docs/api/v1/packages/ai-tools?from=related) — AI SDK tools for the v0 API - [How to add tools to your eve agent](https://vercel.com/kb/guide/how-to-add-eve-tools?from=related) — Add tools to an eve agent by creating a TypeScript file under agent/tools/ with defineTool, and gate sensitive ones on h - [Tools](https://eve.dev/docs/tools?from=related) — Define typed actions the agent can call, and gate sensitive ones on human approval. - [Python](https://vercel.com/docs/ai-gateway/sdks-and-apis/python?from=related) — Use the AI Gateway with Python through OpenAI or Anthropic SDKs with full streaming, tool calling, and async support. - [Chat Completions](https://vercel.com/docs/ai-gateway/sdks-and-apis/openai-chat-completions/chat-completions?from=related) — Create chat completions using the Chat Completions API with support for streaming, image attachments, and PDF documents. Full cross-link map for this page: [/docs/ai-gateway/sdks-and-apis/openai-chat-completions/tool-calling.graph.md](/docs/ai-gateway/sdks-and-apis/openai-chat-completions/tool-calling.graph.md) #### Basic tool calls #### cURL ```bash filename="tool-calls.sh" curl -X POST "https://ai-gateway.vercel.sh/v1/chat/completions" \ -H "Authorization: Bearer $AI_GATEWAY_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "model": "anthropic/claude-opus-5", "messages": [ { "role": "user", "content": "What is the weather like in San Francisco?" } ], "tools": [ { "type": "function", "function": { "name": "get_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"], "description": "The unit for temperature" } }, "required": ["location"] } } } ], "tool_choice": "auto", "stream": false }' ``` #### TypeScript ```typescript filename="tool-calls.ts" import OpenAI from 'openai'; const apiKey = process.env.AI_GATEWAY_API_KEY || process.env.VERCEL_OIDC_TOKEN; const openai = new OpenAI({ apiKey, baseURL: 'https://ai-gateway.vercel.sh/v1', }); const tools: OpenAI.Chat.Completions.ChatCompletionTool[] = [ { type: 'function', function: { name: 'get_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'], description: 'The unit for temperature', }, }, required: ['location'], }, }, }, ]; const completion = await openai.chat.completions.create({ model: 'anthropic/claude-opus-5', messages: [ { role: 'user', content: 'What is the weather like in San Francisco?', }, ], tools: tools, tool_choice: 'auto', stream: false, }); console.log('Assistant:', completion.choices[0].message.content); console.log('Tool calls:', completion.choices[0].message.tool_calls); ``` #### Python ```python filename="tool-calls.py" import os from openai import OpenAI api_key = os.getenv('AI_GATEWAY_API_KEY') or os.getenv('VERCEL_OIDC_TOKEN') client = OpenAI( api_key=api_key, base_url='https://ai-gateway.vercel.sh/v1' ) tools = [ { 'type': 'function', 'function': { 'name': 'get_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'], 'description': 'The unit for temperature' } }, 'required': ['location'] } } } ] completion = client.chat.completions.create( model='anthropic/claude-opus-5', messages=[ { 'role': 'user', 'content': 'What is the weather like in San Francisco?' } ], tools=tools, tool_choice='auto', stream=False, ) print('Assistant:', completion.choices[0].message.content) print('Tool calls:', completion.choices[0].message.tool_calls) ``` > **💡 Note:** **Controlling tool selection:** By default, `tool_choice` is set to `'auto'`, allowing the model to decide when to use tools. You can also:* Set to `'none'` to disable tool calls > * Force a specific tool with: `tool_choice: { type: 'function', function: { name: 'your_function_name' } }` #### Tool call response format When the model makes tool calls, the response includes tool call information: ```json { "id": "chatcmpl-123", "object": "chat.completion", "created": 1677652288, "model": "anthropic/claude-opus-5", "choices": [ { "index": 0, "message": { "role": "assistant", "content": null, "tool_calls": [ { "id": "call_123", "type": "function", "function": { "name": "get_weather", "arguments": "{\"location\": \"San Francisco, CA\", \"unit\": \"celsius\"}" } } ] }, "finish_reason": "tool_calls" } ], "usage": { "prompt_tokens": 82, "completion_tokens": 18, "total_tokens": 100 } } ``` --- [View full sitemap](/docs/sitemap)