What's the difference between tool calling and function calling?

There’s no real difference between tool calling and function calling: they’re names for the same mechanism, used by different vendors. OpenAI and Google’s APIs call it function calling, Anthropic calls it tool use, and tool calling is the vendor-neutral term that covers both. In every case the model is given a schema, a name, a description, and arguments, and emits a structured call against it instead of writing free text.

Where a real distinction sometimes gets drawn: function can imply something narrower, a single deterministic operation with typed inputs and outputs, like a calculator or a database lookup. Tool gets used more loosely to also cover things that are not pure functions: a web search, a code interpreter, a sub-agent, or a whole MCP server exposing several operations behind one connection. That distinction is informal, not a spec boundary, and the two terms get used interchangeably in most writing on the subject, this page included.

See also: What’s the difference between MCP and a plain API call?