Is function calling the same as tool calling?
The Terminology Overlap
The terms are often used interchangeably. OpenAI originally introduced 'function calling' in 2023, and later expanded it to 'tool calling' to encompass functions and other tools like code interpreters or retrieval systems. Anthropic uses 'tool use' similarly. In practice, when someone says 'function calling,' they usually mean the same mechanism as 'tool calling.'
The key difference is scope: a tool can be any external resource the model can invoke, while a function is a specific callable unit in your code. For example, a tool might be a web search API, which is implemented as a function. So all function calls are tool calls, but not all tool calls are functions.
Practical Implications
When building applications, you'll often see APIs that accept a list of 'tools' or 'functions'—the format is nearly identical. For instance, OpenAI's API uses a `tools` parameter where each tool can be a function. The model's output will indicate which tool to call and with what arguments.
Understanding the distinction helps when reading documentation. If a platform says 'tool calling,' it likely supports functions plus possibly other tool types. If it says 'function calling,' it's specifically about functions. But for most developers, the implementation is the same.
- Function calling: model calls a specific function in your code
- Tool calling: broader, can include functions, APIs, or built-in tools
- OpenAI: uses 'tools' parameter, functions are a type of tool
- Anthropic: uses 'tools' and 'tool use'
- In practice, the terms are often used interchangeably
Common mistakes
- Thinking they are completely different; they refer to the same core capability.
- Assuming tool calling always involves functions; it can include other resources like code execution.
- Believing the terminology affects implementation; the underlying mechanism is the same.