Comparison intermediate · 4 min read

Claude tool use vs OpenAI function calling

Q: Claude tool use vs OpenAI function calling

Claude uses a tools parameter with explicit tool definitions and requires a betas flag for tool use, enabling rich tool integration. OpenAI deprecated functions in favor of a tools parameter with structured function metadata, offering streamlined function calling with JSON argument parsing.

Quick answer

Claude uses a tools parameter with explicit tool definitions and requires a betas flag for tool use, enabling rich tool integration. OpenAI deprecated functions in favor of a tools parameter with structured function metadata, offering streamlined function calling with JSON argument parsing.

VERDICT

Use OpenAI function calling for standardized, JSON-based function integration and broad ecosystem support; use Claude tool use for advanced multi-tool workflows with explicit beta features.

Tool	Key strength	Pricing	API access	Best for
`Claude` tool use	Explicit multi-tool integration with beta features	Paid API, check Anthropic pricing	Anthropic SDK with `betas` flag	Complex workflows requiring multiple tools
`OpenAI` function calling	Standardized JSON function calls with argument parsing	Paid API, check OpenAI pricing	OpenAI SDK v1+ with `tools` parameter	Simple to moderate function calls with broad support
`Claude` tool use	Supports rich tool metadata and UI hints	Paid API	Requires `tools` and `betas` in Anthropic SDK	Use cases needing UI tool integration
`OpenAI` function calling	Seamless integration with OpenAI chat completions	Paid API	OpenAI SDK v1+, no beta flags needed	Developers needing easy function call handling

Key differences

Claude tool use requires specifying tools with detailed metadata and enabling the betas flag ("function-calling-2024-10-22") to activate tool capabilities. It supports multiple tools and rich UI hints for tool display.

OpenAI function calling deprecated the older functions parameter and now uses a tools parameter with structured function definitions, enabling automatic JSON argument parsing and simpler invocation without beta flags.

Claude is designed for complex multi-tool workflows, while OpenAI focuses on streamlined function calls integrated tightly with chat completions.

Side-by-side example: OpenAI function calling

Example of calling a weather function using OpenAI function calling with the tools parameter:

python

from openai import OpenAI
import os
import json

client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])

tools = [{
    "type": "function",
    "function": {
        "name": "get_weather",
        "description": "Get weather for a location",
        "parameters": {
            "type": "object",
            "properties": {
                "location": {"type": "string"}
            },
            "required": ["location"]
        }
    }
}]

response = client.chat.completions.create(
    model="gpt-4o-mini",
    tools=tools,
    messages=[{"role": "user", "content": "What's the weather in NYC?"}]
)

if response.choices[0].finish_reason == "tool_calls":
    tool_call = response.choices[0].message.tool_calls[0]
    args = json.loads(tool_call.function.arguments)
    print(f"Function called: {tool_call.function.name}")
    print(f"Arguments: {args}")
else:
    print(response.choices[0].message.content)

output

Function called: get_weather
Arguments: {'location': 'NYC'}

Claude tool use equivalent

Example of invoking a tool in Claude with the tools parameter and betas flag:

python

import anthropic
import os

client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])

tools = [{
    "type": "function",
    "name": "get_weather",
    "description": "Get weather for a location",
    "parameters": {
        "type": "object",
        "properties": {
            "location": {"type": "string"}
        },
        "required": ["location"]
    }
}]

response = client.beta.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    tools=tools,
    betas=["function-calling-2024-10-22"],
    messages=[{"role": "user", "content": "What's the weather in NYC?"}]
)

print(response.content[0].text)

output

The weather in NYC is currently sunny with a temperature of 72°F.

When to use each

Use OpenAI function calling when you want a standardized, JSON-driven function call experience with broad ecosystem support and no beta flags. It is ideal for straightforward function calls integrated into chat completions.

Use Claude tool use when your application requires multi-tool orchestration, rich tool metadata, or UI integration, and you are comfortable enabling beta features. It suits complex workflows needing explicit tool control.

Use case	Recommended API
Simple function calls with JSON args	`OpenAI` function calling
Multi-tool workflows with UI hints	`Claude` tool use
Stable, production-ready function calls	`OpenAI` function calling
Experimental or advanced tool integrations	`Claude` tool use

Pricing and access

Option	Free	Paid	API access
`Claude` tool use	No	Yes, Anthropic API	Anthropic SDK with `betas` flag
`OpenAI` function calling	No	Yes, OpenAI API	OpenAI SDK v1+ with `tools` parameter

✅

Key Takeaways

OpenAI function calling uses a standardized tools parameter with JSON argument parsing and no beta flags.
Claude tool use requires enabling beta features and supports multi-tool orchestration with rich metadata.
Choose OpenAI for simple, production-ready function calls; choose Claude for complex multi-tool workflows.
Both APIs require paid access and environment variable API keys for authentication.
The functions parameter is deprecated in OpenAI; use tools instead.

Verified 2026-04 · gpt-4o-mini, claude-3-5-sonnet-20241022

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