Understanding Tool/Function Calling in LLMs (Step-by-Step Examples in REST and Spring AI)

Tool calling enables LLMs to execute external functions and access live data by requesting function calls with specific parameters. The process involves sending tool definitions to the LLM, receiving function call requests, executing the functions, and returning results for final response generation. While manual REST API implementation requires handling JSON schemas, tool call IDs, and conversation state, Spring AI simplifies this with annotations like @Tool that automatically generate schemas and handle orchestration. Spring AI also supports the Model Context Protocol (MCP) for broader interoperability without additional code.