Claude Tools & Computer Use
Function Calling, Tool Use & Computer Control with Anthropic's API
What are Claude Tools?
Claude's Tool Use (also called Function Calling) allows Claude to interact with external systems, APIs, and databases. You define tools with their names, descriptions, and input schemas—Claude decides when to use them and generates the required parameters. Plus, the new Computer Use feature lets Claude control a computer like a human!
"Claude 3.5 Sonnet is the first frontier AI model to offer computer use in public beta, and we're beginning to explore how it may be applied."
Tool Use
Function calling
Computer Use
Control screens
JSON Schema
Structured inputs
Parallel Calls
Multiple tools
How Tool Use Works
Define Tools
Name, description, schema
Send Message
User query + tools
Claude Decides
Returns tool_use block
Execute & Return
Run tool, send result
Quick Start: Tool Use
Define a weather tool and let Claude use it:
# pip install anthropic
import anthropic
client = anthropic.Anthropic()
# Define your tools
tools = [
{
"name": "get_weather",
"description": "Get current weather for a location",
"input_schema": {
"type": "object",
"properties": {
"location": {
"type": "string",
"description": "City name, e.g., San Francisco"
}
},
"required": ["location"]
}
}
]
# Send message with tools
response = client.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1024,
tools=tools,
messages=[{
"role": "user",
"content": "What's the weather in Tokyo?"
}]
)
# Check if Claude wants to use a tool
for block in response.content:
if block.type == "tool_use":
print(f"Tool: {block.name}")
print(f"Input: {block.input}")Expected Output
Tool: get_weather Input: {"location": "Tokyo"}
Complete Tool Loop
Execute the tool and return the result to Claude:
import anthropic
client = anthropic.Anthropic()
# Your actual tool implementation
def get_weather(location: str) -> dict:
# Call your weather API here
return {
"location": location,
"temperature": "22°C",
"condition": "Partly cloudy"
}
tools = [{
"name": "get_weather",
"description": "Get current weather for a location",
"input_schema": {
"type": "object",
"properties": {
"location": {"type": "string"}
},
"required": ["location"]
}
}]
messages = [{"role": "user", "content": "What's the weather in Paris?"}]
# Agentic loop
while True:
response = client.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1024,
tools=tools,
messages=messages
)
# Check stop reason
if response.stop_reason == "end_turn":
# Claude is done, print final response
for block in response.content:
if hasattr(block, "text"):
print(block.text)
break
# Process tool calls
if response.stop_reason == "tool_use":
messages.append({"role": "assistant", "content": response.content})
tool_results = []
for block in response.content:
if block.type == "tool_use":
# Execute the tool
result = get_weather(**block.input)
tool_results.append({
"type": "tool_result",
"tool_use_id": block.id,
"content": str(result)
})
messages.append({"role": "user", "content": tool_results})Expected Output
"The weather in Paris is currently 22°C and partly cloudy.
It's a pleasant day—perfect for a stroll along the Seine!"
BETA Computer Use
Claude 3.5 Sonnet can control a computer like a human—viewing the screen, moving the cursor, clicking, and typing. This is a breakthrough capability released in October 2024.
What Claude Can Do
- View screenshots of the desktop
- Move cursor to coordinates
- Click buttons and links
- Type text and keyboard shortcuts
- Fill forms, navigate websites
Important Notes
- Still experimental—can make mistakes
- Run in isolated containers (Docker)
- Requires special API header
- 14.9% success on OSWorld benchmark
import anthropic
client = anthropic.Anthropic()
# Computer use requires these special tools
tools = [
{
"type": "computer_20241022",
"name": "computer",
"display_width_px": 1024,
"display_height_px": 768,
"display_number": 1
},
{
"type": "text_editor_20241022",
"name": "str_replace_editor"
},
{
"type": "bash_20241022",
"name": "bash"
}
]
response = client.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=4096,
tools=tools,
betas=["computer-use-2024-10-22"], # Required!
messages=[{
"role": "user",
"content": "Open Firefox and search for 'Anthropic Claude'"
}]
)
# Claude will return computer actions like:
# {"action": "mouse_move", "coordinate": [500, 400]}
# {"action": "click", "button": "left"}
# {"action": "type", "text": "Anthropic Claude"}Controlling Tool Use
Use tool_choice to control
when and how Claude uses tools:
| Option | Behavior |
|---|---|
| {"type": "auto"} | Claude decides whether to use tools (default) |
| {"type": "any"} | Force Claude to use at least one tool |
| {"type": "tool", "name": "..."} | Force a specific tool |
# Force Claude to use the calculator tool
response = client.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1024,
tools=tools,
tool_choice={"type": "tool", "name": "calculator"},
messages=[{"role": "user", "content": "What is 25 * 17?"}]
)Claude Tools vs OpenAI Function Calling
| Aspect | Claude (Anthropic) | OpenAI |
|---|---|---|
| SDK Name | Tool Use | Function Calling |
| Schema Key | input_schema | parameters |
| Response Block | tool_use | function_call / tool_calls |
| Parallel Calls | ✓ Yes | ✓ Yes |
| Computer Use | ✓ Yes (Beta) | ✗ No |
| Built-in RAG | ✗ No | ✓ File Search |
Best Practices
Do
- • Write clear, detailed descriptions
- • Define precise JSON schemas
- • Handle all stop_reason values
- • Validate tool inputs before executing
- • Include examples in descriptions
Don't
- • Run computer use on production systems
- • Trust tool inputs without validation
- • Ignore error responses from tools
- • Use vague tool descriptions
- • Forget to handle parallel tool calls
Supported Models
Claude 3.5 Sonnet
claude-3-5-sonnet-20241022
Best for tools Computer UseClaude 3.5 Haiku
claude-3-5-haiku-20241022
Fast & cheapClaude 3 Opus
claude-3-opus-20240229
Most capable