Tool calling, MCP and acting on the world

Tool calling is what lets a text model touch reality. It emits a structured request, the harness executes it and feeds the result back, and that is how a model runs a command, edits a file, queries a database or hits an API.

Without tools, a model can only describe a fix. With tools, it can apply the fix, run the tests, read the failure and try again. This is the mechanism behind every agent demo a DX Engineer will ship.