Tool calling, MCP and acting on the world

Tool calling is what lets a text model touch reality - run a command, edit a file, query a database, hit an API - by emitting a structured request the harness executes and feeds back.

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 ever ship.