Tool Calling System
AbstractCore provides a universal tool calling system that works across all LLM providers, even those without native tool support.
Table of Contents
Table of Contents Quick Start The @tool Decorator Universal Tool Support Tool Definition Tool Execution Advanced Patterns Error Handling Performance Optimization Tool Syntax Rewriting Event System Integration Best Practices Troubleshooting Examples Related DocumentationTable of Contents
- Quick Start
- The @tool Decorator
- Universal Tool Support
- Tool Definition
- Tool Execution
- Advanced Patterns
- Error Handling
- Performance Optimization
- Tool Syntax Rewriting
- Event System Integration
Quick Start
The simplest way to create and use tools is with the @tool decorator:
from abstractcore import create_llm, tool
@tool
def get_weather(city: str) -> str:
"""Get current weather for a specified city."""
# In a real scenario, you'd call an actual weather API
return f"The weather in {city} is sunny, 72°F"
@tool
def calculate(expression: str) -> float:
"""Perform a mathematical calculation."""
try:
result = eval(expression) # Simplified for demo - don't use eval in production!
return result
except Exception:
return float('nan')
# Works with ANY provider
llm = create_llm("openai", model="gpt-4o-mini")
response = llm.generate(
"What's the weather in Tokyo and what's 15 * 23?",
tools=[get_weather, calculate] # Pass functions directly
)
print(response.content)
# Output: The weather in Tokyo is sunny, 72°F and 15 * 23 = 345.
# By default (`execute_tools=False`), AbstractCore does not execute tools.
# Instead, it returns structured tool calls (if the model chose to call tools).
print(f"Tool calls requested: {len(response.tool_calls) if response.tool_calls else 0}")
print(f"Generation time: {response.gen_time}ms")
print(f"Summary: {response.get_summary()}") # Includes tool count
# Inspect tool calls (host/runtime executes them)
if response.tool_calls:
for call in response.tool_calls:
print(f"Tool: {call.get('name')} args={call.get('arguments')}")
The @tool Decorator
The @tool decorator is the primary way to create tools in AbstractCore. It automatically extracts function metadata and creates proper tool definitions.
Basic Usage
from abstractcore import tool
@tool
def list_files(directory: str = ".", pattern: str = "*") -> str:
"""List files in a directory matching a pattern."""
import os
import fnmatch
try:
files = [f for f in os.listdir(directory)
if fnmatch.fnmatch(f, pattern)]
return "\n".join(files) if files else "No files found"
except Exception as e:
return f"Error: {str(e)}"
Type Annotations
The decorator automatically infers parameter types from type annotations:
@tool
def create_user(name: str, age: int, is_admin: bool = False) -> str:
"""Create a new user with the specified details."""
user_data = {
"name": name,
"age": age,
"is_admin": is_admin,
"created_at": "2025-01-14"
}
return f"Created user: {user_data}"
Enhanced Metadata
The @tool decorator supports rich metadata that gets automatically injected into system prompts for prompted models and passed to native APIs:
@tool(
description="Search the database for records matching the query",
tags=["database", "search", "query"],
when_to_use="When the user asks for specific data from the database or wants to find records",
examples=[
{
"description": "Find all users named John",
"arguments": {
"query": "name=John",
"table": "users"
}
},
{
"description": "Search for products under $50",
"arguments": {
"query": "price<50",
"table": "products"
}
},
{
"description": "Find recent orders",
"arguments": {
"query": "date>2025-01-01",
"table": "orders"
}
}
]
)
def search_database(query: str, table: str = "users") -> str:
"""Search the database for records matching the query."""
# Implementation here
return f"Searching {table} for: {query}"
How This Metadata is Used:
- Prompted tool calling: the tool formatter injects tool name/description/args into the system prompt. To keep prompts small, when_to_use is included only for small tool sets and a few high-impact tools (edit/write/execute + web triage tools), and tool examples are globally capped.
- Native tool calling: only standard fields (name, description, parameters) are sent to provider APIs (unknown/custom fields are intentionally omitted for compatibility).
Built-in Tools
AbstractCore includes a comprehensive set of ready-to-use tools in abstractcore.tools.common_tools (requires pip install "abstractcore[tools]"):
from abstractcore.tools.common_tools import skim_url, fetch_url, search_files, read_file, list_files
# Quick URL preview (fast, small)
preview = skim_url("https://example.com/article")
# Full web content fetching and parsing (HTML→Markdown, JSON/XML/text)
result = fetch_url("https://api.github.com/repos/python/cpython")
# For PDFs/images/other binaries, fetch_url returns metadata (and optional previews), not full extraction.
# File system operations
files = search_files("def.*fetch", ".", file_pattern="*.py")
content = read_file("config.json")
directory_listing = list_files(".", pattern="*.py", recursive=True)
Available Built-in Tools:
- skim_url - Fast URL skim (title/description/headings + short preview)
- fetch_url - Fetch + parse common text-first types (HTML→Markdown, JSON/XML/text); binaries return metadata + optional previews
- search_files - Search for text patterns inside files using regex
- list_files - Find and list files by names/paths using glob patterns
- read_file - Read file contents with optional line range selection
- write_file - Write content to files with directory creation
- edit_file - Edit files using pattern matching and replacement
- web_search - Search the web using DuckDuckGo
- skim_websearch - Smaller/filtered web search (compact result list)
- execute_command - Execute shell commands safely with security controls
Suggested web workflow (agent-friendly):
1. skim_websearch(...) → get a small set of candidate URLs
2. skim_url(...) → quickly decide what’s worth fetching
3. fetch_url(...) → parse the selected URL(s); set include_full_content=False when you want a smaller output
Tip: you can measure output footprint/latency locally with python examples/skim_tools_benchmark.py --help.
Real-World Example
Here's an example from AbstractCore's codebase showing the enhanced @tool decorator:
@tool(
description="Find and list files and directories by their names/paths using glob patterns (case-insensitive, supports multiple patterns)",
tags=["file", "directory", "listing", "filesystem"],
when_to_use="When you need to find files by their names, paths, or file extensions (NOT for searching file contents)",
examples=[
{
"description": "List all files in current directory",
"arguments": {
"directory_path": ".",
"pattern": "*"
}
},
{
"description": "Find all Python files recursively",
"arguments": {
"directory_path": ".",
"pattern": "*.py",
"recursive": True
}
},
{
"description": "Find all files with 'test' in filename (case-insensitive)",
"arguments": {
"directory_path": ".",
"pattern": "*test*",
"recursive": True
}
},
{
"description": "Find multiple file types using | separator",
"arguments": {
"directory_path": ".",
"pattern": "*.py|*.js|*.md",
"recursive": True
}
},
{
"description": "Complex multiple patterns - documentation, tests, and config files",
"arguments": {
"directory_path": ".",
"pattern": "README*|*test*|config.*|*.yml",
"recursive": True
}
}
]
)
def list_files(directory_path: str = ".", pattern: str = "*", recursive: bool = False, include_hidden: bool = False, head_limit: Optional[int] = 50) -> str:
"""
List files and directories in a specified directory with pattern matching (case-insensitive).
IMPORTANT: Use 'directory_path' parameter (not 'file_path') to specify the directory to list.
Args:
directory_path: Path to the directory to list files from (default: "." for current directory)
pattern: Glob pattern(s) to match files. Use "|" to separate multiple patterns (default: "*")
recursive: Whether to search recursively in subdirectories (default: False)
include_hidden: Whether to include hidden files/directories starting with '.' (default: False)
head_limit: Maximum number of files to return (default: 50, None for unlimited)
Returns:
Formatted string with file and directory listings or error message.
When head_limit is applied, shows "showing X of Y files" in the header.
"""
# Implementation here...
How This Gets Transformed
When you use this tool with a prompted model (like Ollama), AbstractCore automatically generates a system prompt like this:
You are a helpful AI assistant with access to the following tools:
**list_files**: Find and list files and directories by their names/paths using glob patterns (case-insensitive, supports multiple patterns)
• When to use: When you need to find files by their names, paths, or file extensions (NOT for searching file contents)
• Tags: file, directory, listing, filesystem
• Parameters: {"directory_path": {"type": "string", "default": "."}, "pattern": {"type": "string", "default": "*"}, ...}
To use a tool, respond with this EXACT format:
<|tool_call|>
{"name": "tool_name", "arguments": {"param1": "value1", "param2": "value2"}}
</|tool_call|>
**EXAMPLES:**
**list_files Examples:**
1. List all files in current directory:
<|tool_call|>
{"name": "list_files", "arguments": {"directory_path": ".", "pattern": "*"}}
</|tool_call|>
2. Find all Python files recursively:
<|tool_call|>
{"name": "list_files", "arguments": {"directory_path": ".", "pattern": "*.py", "recursive": true}}
</|tool_call|>
... and 3 more examples with proper formatting ...
Universal Tool Support
AbstractCore's tool system works across all providers through two mechanisms:
Control Tokens vs Tool Transcript Tags (Important)
It’s easy to conflate two separate layers:
1) Chat-template control tokens (provider responsibility)
- These are the hidden/model-specific role separators that turn {role:"system"} vs {role:"user"} into the model’s expected prompt template.
- Examples (model-dependent): Llama role headers, Qwen im_start blocks, etc.
- When you use a messages API (OpenAI-compatible, Anthropic, Ollama, LMStudio), the server usually applies these automatically.
2) Tool-call transcript tags (prompted strategy)
- These are literal strings the model emits in assistant content that we parse, such as:
- Qwen-style: <|tool_call|>…</|tool_call|>
- LLaMA-style: <function_call>…</function_call>
- XML-ish: <tool_call>…</tool_call>
- They may correspond to special tokens in some tokenizers, but in prompted mode we still treat them as transcript text and parse them from the output.
Native tool calling uses structured request/response fields (tools / tool_calls / Anthropic tool_use) and relies on the provider/server to apply the correct chat template; prompted tool calling describes tools in the system prompt and expects transcript tags in assistant text.
1. Native Tool Support
For providers with native tool APIs (OpenAI, Anthropic):
# OpenAI with native tool support
llm = create_llm("openai", model="gpt-4o-mini")
response = llm.generate("What's the weather?", tools=[get_weather])
2. Intelligent Prompting
For providers without native tool support (Ollama, MLX, LMStudio):
# Ollama without native tool support - AbstractCore handles this automatically
llm = create_llm("ollama", model="qwen3:4b-instruct")
response = llm.generate("What's the weather?", tools=[get_weather])
# AbstractCore automatically:
# 1. Detects the model architecture (Qwen3)
# 2. Formats tools with examples into system prompt
# 3. Parses tool calls from response using <|tool_call|> format
# 4. Returns structured tool call requests in response.tool_calls
Tool Definition
Tools are defined using the ToolDefinition class, but the @tool decorator handles this automatically:
from abstractcore.tools import ToolDefinition
# Manual tool definition (rarely needed)
tool_def = ToolDefinition(
name="get_weather",
description="Get current weather for a city",
parameters={
"city": {
"type": "string",
"description": "The city name"
}
},
function=get_weather_function
)
Parameter Types
Supported parameter types:
string- Text valuesinteger- Whole numbersnumber- Floating-point numbersboolean- True/false valuesarray- Lists of valuesobject- Complex nested structures
@tool
def complex_tool(
text: str,
count: int,
threshold: float,
enabled: bool,
tags: list,
config: dict
) -> str:
"""Tool with various parameter types."""
return f"Processed: {text} with {count} items"
Tool Execution
Execution Modes
- Passthrough mode (default):
execute_tools=False - AbstractCore returns structured tool calls in
GenerateResponse.tool_calls. - By default (
tool_call_tags is None), tool-call markup is stripped fromGenerateResponse.content. -
A host/runtime executes tools (recommended for servers and agent loops).
-
Direct execution mode (deprecated):
execute_tools=True - AbstractCore parses and executes tools locally via the tool registry and appends results to
content. - Intended for simple scripts only; avoid in server/untrusted environments.
Architecture-Aware Tool Call Detection
AbstractCore automatically detects model architecture and uses the appropriate tool call format:
| Architecture | Format | Example |
|---|---|---|
| Qwen3 | <|tool_call|>...JSON...</|tool_call|> |
<|tool_call|>{"name": "get_weather", "arguments": {"city": "Paris"}}</|tool_call|> |
| LLaMA3 | <function_call>...JSON...</function_call> |
<function_call>{"name": "get_weather", "arguments": {"city": "Paris"}}</function_call> |
| OpenAI/Anthropic | Native API tool calls | Structured JSON in API response |
| XML-based | <tool_call>...JSON...</tool_call> |
<tool_call>{"name": "get_weather", "arguments": {"city": "Paris"}}</tool_call> |
Note: AbstractCore handles architecture detection, prompt formatting, and response parsing automatically. Your tools work the same way across all providers.
Execution Responsibility (Recommended)
In passthrough mode, response.tool_calls are tool call requests. Execute them in your host/runtime (and apply your own safety policy) before sending tool results back to the model in a follow-up turn.
Advanced Patterns
Tool Chaining
Tools can call other tools or return data that triggers additional tool calls:
@tool
def get_user_location(user_id: str) -> str:
"""Get the location of a user."""
# Simulated implementation
locations = {"user123": "Paris", "user456": "Tokyo"}
return locations.get(user_id, "Unknown")
@tool
def get_weather(city: str) -> str:
"""Get weather for a city."""
return f"Weather in {city}: 72°F, sunny"
# LLM can chain these tools:
response = llm.generate(
"What's the weather like for user123?",
tools=[get_user_location, get_weather]
)
# In an agent loop, your host/runtime can execute tool calls and feed tool results back into the model for multi-step chaining.
Conditional Tool Execution (Recommended)
In passthrough mode, your host/runtime decides which tool calls to execute:
from abstractcore.tools import ToolCall, ToolRegistry
dangerous_tools = {"delete_file", "system_command", "send_email"}
registry = ToolRegistry()
registry.register(get_user_location)
registry.register(get_weather)
response = llm.generate("What's the weather like for user123?", tools=[get_user_location, get_weather])
for call in response.tool_calls or []:
name = call.get("name")
if name in dangerous_tools:
continue
result = registry.execute_tool(
ToolCall(
name=name,
arguments=call.get("arguments") or {},
call_id=call.get("call_id") or call.get("id"),
)
)
print(result)
Async Tool Support
For tools that need to perform async operations:
import asyncio
@tool
def fetch_data(url: str) -> str:
"""Fetch data from a URL."""
async def async_fetch():
# Simulate async HTTP request
await asyncio.sleep(0.1)
return f"Data from {url}"
# Run async function in sync context
loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)
try:
result = loop.run_until_complete(async_fetch())
return result
finally:
loop.close()
Error Handling
Tool-Level Error Handling
Handle errors within tools:
@tool
def safe_division(a: float, b: float) -> str:
"""Safely divide two numbers."""
try:
if b == 0:
return "Error: Division by zero is not allowed"
result = a / b
return f"{a} ÷ {b} = {result}"
except Exception as e:
return f"Error: {str(e)}"
System-Level Error Handling
AbstractCore provides comprehensive error handling:
from abstractcore.exceptions import ToolExecutionError
try:
response = llm.generate("Use the broken tool", tools=[broken_tool])
except ToolExecutionError as e:
print(f"Tool execution failed: {e}")
print(f"Failed tool: {e.tool_name}")
print(f"Error details: {e.error_details}")
Validation and Sanitization
Validate tool inputs:
@tool
def create_file(filename: str, content: str) -> str:
"""Create a file with the given content."""
import os
import re
# Validate filename
if not re.match(r'^[a-zA-Z0-9_.-]+$', filename):
return "Error: Invalid filename. Use only letters, numbers, dots, dashes, and underscores."
# Prevent directory traversal
if '..' in filename or filename.startswith('/'):
return "Error: Invalid filename. No directory traversal allowed."
try:
with open(filename, 'w') as f:
f.write(content)
return f"File '{filename}' created successfully"
except Exception as e:
return f"Error creating file: {str(e)}"
Performance Optimization
Tool Registry
Use the tool registry for better performance with many tools:
from abstractcore.tools import ToolRegistry, register_tool
# Register tools globally
register_tool(get_weather)
register_tool(calculate)
register_tool(list_files)
# Use registered tools
registry = ToolRegistry.get_instance()
available_tools = registry.get_all_tools()
response = llm.generate(
"Help me with weather and calculations",
tools=available_tools
)
Lazy Loading
Load expensive resources only when needed:
class DatabaseTool:
def __init__(self):
self._connection = None
@property
def connection(self):
if self._connection is None:
# Expensive database connection
self._connection = create_database_connection()
return self._connection
db_tool = DatabaseTool()
@tool
def query_database(sql: str) -> str:
"""Execute a SQL query."""
try:
result = db_tool.connection.execute(sql)
return str(result)
except Exception as e:
return f"Database error: {str(e)}"
Caching Results
Cache expensive tool results:
from functools import lru_cache
@tool
@lru_cache(maxsize=100)
def expensive_calculation(input_data: str) -> str:
"""Perform an expensive calculation with caching."""
import time
time.sleep(1) # Simulate expensive operation
return f"Result for {input_data}"
Tool Syntax Rewriting
AbstractCore can rewrite tool-call syntax for downstream agents/clients:
- Python API: pass
tool_call_tags=...togenerate()/agenerate()/BasicSession.generate()to preserve and rewrite tool-call markup incontent. - HTTP server: set the
agent_formatrequest field (or rely on auto-detection based onUser-Agent+ model name).
See: Tool Call Syntax Rewriting
Event System Integration
Observe tool calling and (optional) tool execution through events:
Cost Monitoring
from abstractcore.events import EventType, on_global
def monitor_tool_costs(event):
"""Monitor costs of tool executions."""
for call in event.data.get("tool_calls", []) or []:
if call.get("name") in {"expensive_api_call", "premium_service"}:
print(f"Warning: Using expensive tool {call.get('name')}")
on_global(EventType.TOOL_STARTED, monitor_tool_costs)
Performance Tracking
def track_tool_performance(event):
"""Track tool execution outcomes (shape varies by emitter)."""
for result in event.data.get("tool_results", []) or []:
if result.get("success") is False:
print(f"Tool failed: {result.get('name')} error={result.get('error')}")
on_global(EventType.TOOL_COMPLETED, track_tool_performance)
Security Auditing
def audit_tool_usage(event):
"""Audit all tool usage for security."""
for call in event.data.get("tool_calls", []) or []:
print(f"Tool requested: {call.get('name')} args={call.get('arguments')}")
# Log to security audit system
security_log(call.get("name"), call.get("arguments"))
on_global(EventType.TOOL_STARTED, audit_tool_usage)
Best Practices
1. Clear Documentation
Always provide clear docstrings for your tools:
@tool
def send_email(to: str, subject: str, body: str) -> str:
"""Send an email to the specified recipient.
Args:
to: Email address of the recipient
subject: Subject line of the email
body: Main content of the email
Returns:
Success message or error description
Note:
This tool requires email configuration to be set up.
Use with caution as it sends actual emails.
"""
# Implementation here
2. Input Validation
Always validate and sanitize inputs:
@tool
def process_user_input(user_data: str) -> str:
"""Process user input safely."""
# Validate input length
if len(user_data) > 1000:
return "Error: Input too long (max 1000 characters)"
# Sanitize input
import html
safe_data = html.escape(user_data)
# Process safely
return f"Processed: {safe_data}"
3. Error Recovery
Provide meaningful error messages and recovery suggestions:
@tool
def connect_to_service(endpoint: str) -> str:
"""Connect to an external service."""
try:
# Attempt connection
result = make_connection(endpoint)
return f"Connected successfully: {result}"
except ConnectionError:
return "Error: Could not connect to service. Please check the endpoint URL and try again."
except TimeoutError:
return "Error: Connection timed out. The service may be temporarily unavailable."
except Exception as e:
return f"Error: Unexpected error occurred: {str(e)}"
4. Resource Management
Clean up resources properly:
@tool
def process_large_file(filename: str) -> str:
"""Process a large file efficiently."""
try:
with open(filename, 'r') as file:
# Process file in chunks
result = ""
while True:
chunk = file.read(1024)
if not chunk:
break
result += process_chunk(chunk)
return f"Processed file: {filename}"
except FileNotFoundError:
return f"Error: File '{filename}' not found"
except MemoryError:
return "Error: File too large to process"
Troubleshooting
Common Issues
- Tool not being called: Check tool description and parameter names
- Invalid JSON in tool calls: Ensure proper error handling in tools
- Tools timing out: Implement proper timeout handling
- Memory issues with large tools: Use streaming or chunking
Debug Mode
Enable debug mode to see tool execution details:
import logging
logging.basicConfig(level=logging.DEBUG)
# Tool execution details will be logged
response = llm.generate("Use tools", tools=[debug_tool])
Testing Tools
Test tools independently:
# Test tool directly
result = get_weather("Paris")
print(f"Direct call result: {result}")
# Test with LLM
response = llm.generate("What's the weather in Paris?", tools=[get_weather])
print(f"LLM result: {response.content}")
Examples
See the examples directory for comprehensive tool usage examples:
Related Documentation
- API Reference - Complete API documentation
- Event System - Event-driven tool control
- Architecture - System design and tool execution flow
- Server Guide - HTTP server and REST API
- Getting Started - Quick start guide