What is Tool Calling?
TL;DR
The mechanism that enables AI agents to invoke external APIs and functions to execute real-world tasks. The core technology behind agentic AI.
Tool Calling: Definition & Explanation
Tool Calling (also known as Function Calling) is the mechanism that enables AI models to do more than generate text — they can invoke external functions and APIs to perform real-world operations. For example, when a user asks 'What's the weather in Tokyo tomorrow?', the AI calls a weather API to retrieve current forecast data and uses it to generate its response. It is offered as a standard feature by major AI API providers including OpenAI, Anthropic, Google, and Mistral, and serves as the core technology that enables AI agents to actually 'execute' tasks. In 2026, standardization through MCP (Model Context Protocol) has progressed, creating an environment where the same set of tools can be uniformly accessed from different AI models. The scope of tool calling is expanding rapidly to include web browsing, email sending, database operations, file management, and integration with external SaaS services.